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Mary E. Mendoza, "Deadly Divide: How Insects, Pathogens, and People Defied the US-Mexico Border" (UNC Press, 2026)
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Mary Mendoza
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Stephen Haussman
Welcome to the New Books Network welcome back to the New Books Network. I'm your host, Stephen Haussman. I'm an assistant professor in the History Department at Appalachian State University in Western North Carolina. And to hear more interviews like this one, subscribe to my channel, which is New Books in the American West. For today's episode, I'm very excited to be speaking with Mary Mendoza. Dr. Mendoza is an assistant professor of history at Penn State University, and today we'll be discussing her new book, Daily Deadly Divide How Insects, Pathogens, and People Defied the US Mexico border, which is brand new, just came out with the University of North Carolina Press, like a couple weeks ago here in June 2026. Welcome to the New Books Network. Mary, good to have you here today.
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Mary Mendoza
Thank you so much for having me. It's so wonderful to be here with you.
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Stephen Haussman
Why don't we start, as we always do on this show, by just hearing a little bit about yourself? I'd love to hear a little about your background. And in particular, I'm interested in how you became interested in.
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Mary Mendoza
Well, I am from San Antonio, Texas, so I grew up a couple hours away from the nearest point on the US Mexico border. I'm Mexican American. My dad is a bricklayer, very good bricklayer. I'm very proud of all the work he does. And I think I grew up around a lot of people moving back and forth across the border. A lot of the men he worked with I was around as a kid and they would kind of cross the border regularly. And I also knew of border crossing stories and my own family. Even if sometimes we didn't want to acknowledge some of those stories, they were sort of there in the background. And I was always really interested in that. And then as I got a little bit older, I became interested actually in foreign languages because we had to take a foreign language to graduate high school. And at first I was a little reluctant and I was like, I was, you know, I've been told I need to just focus on my American ness. I'm a Mexican American, but I really need to just be like an American. And I kind of didn't want to take Spanish. And then I did, and I had this really great teacher. Her name was Gail Glover. And she kind of opened something in me that got me really interested, not just in Spanish, but in all languages. But I feel like that Spanish connection, really, it connected me and brought me back to myself and my heritage. And then I went to college at Middlebury, thanks to Gail, and I really fell in love with history there. I thought I was going to go and study foreign languages, which I did do, but then I took history classes and I couldn't stop. And so I ended up becoming a historian. I wrote a thesis about the US Mexico border as an undergrad. And then from there I knew I was going to go to grad school, but I took a few years off before I did that. So that's kind of my quick, quick, but also long path to becoming a historian.
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Stephen Haussman
You know, I asked that question of all of my guests and, you know, you get a range of answers, but One commonality that almost all, maybe not all, but almost all of the folks that I asked that of, you know, is. Is there's usually a teacher somewhere in there that. That pushes them at a really critical point in. In a direction. And it sounds like your story is no different.
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Mary Mendoza
Yeah, and very common.
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Stephen Haussman
So you mentioned this a little bit, but could you talk a little bit more specifically about what brought you to the topic of this book? I'd love to hear a little bit about the path to writing Deadly Divide specifically and what the writing process was like.
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Mary Mendoza
Yeah, so I mentioned I wrote this undergraduate thesis. It was an optional thesis. I actually did not Wamp wamp. I did not major in history. I majored in something called International Studies, which was history adjacent. And in that major you had to pick an area of focus, like a discipline. And I did pick history. So I was like. Like a shadow history major or something. I was like in the. In the shadows. Anyway, it was a weird thing. And in that type of major you had to also pick a region. I did Latin America, so I did Latin American history. And then you didn't have to write a thesis, but I opted to. And as I was thinking about what I wanted to write about, I had taken a lot of history classes. I'd also taken like, a lot of languages. And I wanted to figure out a way to use language skills in my work. And ultimately I asked a bunch of questions about the things I grew up around. Right. The things I just mentioned earlier. Why were all these people able to move back and forth? How is it getting more and more difficult? I would talk to my dad and he would say that sometimes the people he worked with would have trouble getting back across the border. And so I wanted to know why and how. And I started to think about what we've been doing. And this is the early 2000s, right after. This is after 9 11. But as the secure Fence act was really being kind of put into place. And so my question was, why? Why? And when did we start building fences? There wasn't really an environmental angle. It was a very undergrad y kind of specific, very easy question. But I did write this thesis. And so I. I found that I was super interested as I started to do research. And that ultimately became the foundation for this book. I wrote it under the direction of Cathy Morse and Maricela Ramos, who was here. Who was at Middlebury at the time. I say here, who was at Middlebury at the time. And it was a really wonderful experience and it got me very curious. So I decided to pursue that topic in graduate school. But as a. Developed as a scholar, I think my questions became much more environmental because I thought, well, this fence must be doing something to the nature in which it exists. And I thought. I still thought the story was going to be simpler than it turned out. I thought it was going to be like, yes, of course, the wildlife is being destroyed and the plants, the flora, the fauna. But it was as. As is often the case with environmental history, it was much more dynamic than I anticipated.
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Stephen Haussman
So you've been sitting with this project then, for quite a while. If it's sort of the kernel or the grain of it was an undergrad, then. You've been working on this for a long time?
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Mary Mendoza
Yeah, I finished my undergraduate thesis in 2006 and the book came out in 2026, which is quite a long time for a first book, but I wasn't consistently working on it that whole time.
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Stephen Haussman
Well, let's get into the story that you tell in this book a bit. And you begin Deadly Divide with your own visit to the US Mexico Bor. Your own reflections on what the border has meant to you in your life. And you touched on this a bit earlier, but maybe you can go into a little bit more depth and tell us about that visit in particular and those reflections and thoughts that you had while looking at the ocean and the border itself.
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Mary Mendoza
Yeah, that was really a special trip, the trip that I opened the book with. It was a trip that, as I discuss in the prologue, that I really put off for a very long time. I had been researching throughout graduate school for years, going to different parts of the border. I went to the westernmost part of the border, the. The. Where the fence goes into the ocean. I don't know how many times by that point. And I just really avoided visiting points along the Texas Mexico border. I traveled through New Mexico and traveled through Arizona. But Texas was hard because my family, who is Mexican American, really worried for some reason when I was in Texas, like when I was basically in there in their relative arm's reach, right. I. They didn't want me to go because they could kind of control. Not control, but kind of control what I was doing. And so there are a lot of arguments with my parents, with my grandparents, don't go. It's really dangerous there. And I think when I was at a greater distance, they were a little bit more like, well, what we don't know won't hurt us. Like, she's far away. And so we're not really that worried. And so I avoided it to not have these arguments, but at some point I was getting close to finishing this project and I was like, I, I have to do this. And so I went down to the easternmost point I could drive to, which was like on a little dirt road, stopped, walked to the, to the beach. And I had this just like surreal experience of walking down the beach to this point where the, where the river opens up into the Gulf of Mexico. And as I was walking, I just had like this flood of like my own childhood kind of come back to me. Like going to the beach as a kid and looking at these like, very, very specific to Texas oceans and beaches with like remnants of oil spills and like fish carcasses and like a very particular smell. Like not the nicest beaches in the world for sure, but also like the beaches we had. And then walking down, not seeing a single person was just so mind blowing in a way because one, it was lush and green and gorgeous and two, everything, even my research to some extent, but mostly the media constructs and my own family with their fear about me going had constructed, really told me, like, be, be, be careful, there might be border patrol people all over the place, there might be migrants crossing, try going to try to ask you for things and you're by yourself. Like I was alone. And so it was just a really cool thing to walk down the beach, have this flood of memories and then get there and see the mighty river just sort of opening up in this beautiful way into the ocean and see not a single person, not a single watchtower, not a single sign of any of the things that we think we would see. It struck me as almost unbelievable and it just sort of, you know, brought a lot of things to mind, as the reader can see when they read the rest of the prologue. But it was quite a lovely, a lovely experience. I have always loved the border, so it made me happy to see this space that was a little bit left alone.
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Stephen Haussman
Well, let's get into the history of the border itself and let's begin toward the start of kind of the early 20th century, which in some ways is kind of the birth of what we might call the modern border, the militarized border that is often thought of today, you were just talking about, that is used in political sort of rhetoric and is shown on the news and things. And in the book, you describe the importance of a tiny insect to beginning this story. What is that insect? And what is the story here?
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Mary Mendoza
So one of the things I really like to think about as an environmental historian is how nature mediates and affects social relationships and categories like race. Right. In essence, how does nature or parts of nature, like an insect, like a tick, affect the ways that we think about and treat each other? Right. Day to day? And so when I was researching, I came across, thanks to Rachel St John and her book, some footnotes from her work, and then some other documents just in the archive that kind of alluded to border fences being constructed in response to some kind of, like, insect issue. And so I dug a little further, I dug deeper, and there was this tick called the Texas fever tick that caused a disease in cattle. And what was particularly interesting and problematic about it is that every cow that was exposed to this tick before it was six months old would develop immunity. So any cattle that lived basically where the tick thrived and existed everywhere. So places like Texas, places like Mexico, places like Georgia, places in the southern US Would develop immunity. But if those cattle traveled north and mingled with adult cows or steers, they would then bring the tick to those animals, and those animals would then get infected and develop this fever that would kill them. They would get really sick and die. And so as the United States opened up and westward expansion continues in the Mexican session happens, people start grazing in the far western landscapes. And in the Northwest, the cattle trade really had already been well established, but it really starts to boom. And people are sending cows from, from Mexico and Texas up to Kansas. And then in Kansas, they're going east, they're going west, they're going north. And so they're really mixing in ways they might not have mixed as much before. I mean, they were mixing before, but it was much slower. The railroad really shifted that a lot, as Richard White writes about. And so cattle were starting to mingle in ways they hadn't before. And so cows that hadn't been exposed started getting sick and dying and in really large numbers. And at first nobody understood why. And then they started to guess, well, are we moving the cattle too quickly? Is this an issue of acclimat? Are cows excreting something as they move north too quickly that other cattle then eat and die from? There were all kinds of really interesting questions that reflected 19th century ideas about body and interactions with the environment in that way. But then eventually the US Department of Agriculture did a study. It was a very young agency at the time, and it figured out by the 1880s that the. I guess a little later than that. But it, Starting in the 1880s, it started a study that ultimately discovered that the disease vector was this tick like I've described. They didn't quite Know about the immunity thing right away. That was later to be discovered. So they started to work on figuring out where the tick thrived in the United States. They did figure it out. They made a quarantine line and ultimately designed a way to push the tick out of the United States, which is great, right? Because then cattle could move, say, from Texas up to Montana, and the cattle in Montana would be safe. But it became a problem because Mexico didn't do the same thing. They did not eradicate the tick. They had no reason to, because their entire nation was within the sort of zone or range where the tick could live. And so the border had to be a place where they quarantined cattle if they crossed the border. Okay, now this gets really complicated, because sometimes cows in Texas or southern California would wander south of the border and they'd need to be brought back, but they'd walk through places that had ticks in them. So ranchers were then required to take their own cattle that they had accidentally lost, round them up, take them to a port of entry, which could be hundreds of miles away, and bring them back across the border. But in bringing them back, they had to have the cow be dipped in arsenic twice and then quarantined in a pasture for 60 days before they could then return the animal back to its home ranch, which was kind of a lot and kind of annoying. And so ranchers started getting mad. Other animals coming from Mexico also had to be quarantined, which also enraged ranchers who just wanted to trade for, say, butchering and things like that. But the crux of my argument here really rests on these, like, accidental movement, like where cattle went south and needed to come back. Because ranchers in the United States started to say things like, my cow is an American, and therefore it should get to come back to the United States without any of this rigmarole. Like, this is an annoying, bureaucratic thing that should really only be applied to Mexican cattle. And at first, the department of agriculture said, you know what? Sorry, any animal that runs through tick infested country is subject to this quarantine. But over time, because they got so many complaints, the USDA continued to enforce their rule. But they started to adopt very similar language. Oh, yes, Mexican cattle are infested with ticks, and therefore, we should quarantine against them. So what you start to see is, like, a racialization of cattle in a particular way. And when I say that, I really mean people start to place these moral hierarchies on things based on place of origin. So in some ways. Yes, it's nationality, but nationality gets blurred with race and ethnicity all the time. And here we see it being applied to animals rather than people. It's not something necessarily phenotypic. It's something completely based on place and environment. And so my larger argument is that this little bug started this very large debate about what was clean and safe and pure and okay and what was good and what was really bad and tick infested and dirty and filthy. And these ideas got applied to the whole landscape of Mexico. So we start to see these ideas about filthy, diseased and dirty later get projected onto Mexican people in ways that really stick and harden the ways that we think about race at the border.
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Mary Mendoza
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Stephen Haussman
Almost.
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Mary Mendoza
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Stephen Haussman
You know I have to ask one quick follow up question to that that occurred to Me, when you were telling that really interesting story on earth in like 1907, do you dip a cow in arsenic? How do you manage that?
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Mary Mendoza
Oh, this is. Oh, I love spending time in the National Agricultural Library. If anyone has any border related history or even just ag related history, that place is amazing. The library is awesome. They have all of these, like, here's how we figured out it was arsenic. And then here is what we did, and here are all of these like slides that show just how well the ticks respond to basically being killed based on this thing or that thing. And arsenic was the best thing. So they built these vats, they dug a hole in the ground and there was a ramp. And a cow would sort of walk kind of down a ramp, but then it would essentially just fall into this thing that was about as deep as a cow's height and it would be almost completely submerged in this big huge thing of arsenic. And then there was a slotted ramp on the other side. And the thing was, I don't know, several feet long. And it would walk through it and then it would come up this other ramp and the slotted ramp would let all of the arsenic dripping off the cow go back into the vat and then they would go out through a chute and then they'd come back and they do it one more time and then they'd go into a pasture. Yeah, it was quite an enterprise.
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Stephen Haussman
Wild. Yeah. Those poor cows, they probably were very confused and distraught by that, I would imagine.
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Mary Mendoza
Yeah. You know, this was not a time when people were really thinking about animal well being. And that is very clear when we look at these images.
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Stephen Haussman
So there's a turn of phrase that you use in the book, kind of a description of what you're doing in this book that I liked a lot. You talk about how the non human environment came to be a tool for mediating power along the border in the early 20th century. And putting it like that really kind of clarified a lot of what the environment is doing in this book and how people use the environment in general. And that process is done not just through ticks, but through other small life forms as well. So can you explain a bit what you meant by that and sort of how other small animals come to be these kind of mediating factors in power relations at the border.
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Mary Mendoza
Yeah, so I think the best example from the book for this would really be the body louse. And I think that because in the context of the tick which we have now discussed, it's really interesting to see how when in 1916, which I should say is 10 years after a successful tick eradication campaign and five years after the construction of the first border fence to stop cattle from wandering south and north, really, there was an outbreak of typhus in southern Texas. In South Texas, 68 people got sick, 14 people died. And this is a pretty well documented story amongst borderlands public health scholars. John McKiernan Gonzalez wrote about it, Natalia Molina has written about it, Alexandra Van Astern has written about it. And so this is by no means like a new story to the historiography, but I do think that in the context of the tick and thinking about it as using the louse as the center of the story, we can reshape how we're considering the way that these power dynamics in the borderland shift. For example, typhus was a disease caused by a body loss, also discovered around the same time that the tick was discovered to be a vector for disease. This was a new moment where we were really learning that bugs can transmit disease. It was a pretty big deal and very cool scientifically. But once this outbreak in Texas happens, it's interesting because everything in the United States in terms of typhus and the way we talk about typhus shifted from typhus is a disease of the poor, which I should note was already endemic to the United States. There were cases in Chicago, New York, Baltimore, San Francisco, places very far from the border, and also San Diego, El Paso, places very near the border. Right. So typhus already existed, and it was very much associated with class and hygiene. So people who lived in structural conditions that kept them from things like regular bathing or living in crowded spaces with lots of other people generally caused conditions that allowed the body louse to proliferate and cause this disease. But then this thing happens at the border, and the US Public Health Service rushes down and they start this quarantine campaign, basically saying all Mexicans crossing the border need to be deloused, ultimately dipped like ticks. I mean, I'm sorry, like cows, to get these bugs off of their bodies. And they don't say, we don't want Mexicans to come in, but they do say, we don't want body lice on Mexicans to come in. And so there's this whole campaign to force Mexicans to these bath houses that are checkpoints along the border where they will strip entirely naked. Their clothes go into a large steamer while they are sprayed with a mixture of kerosene and vinegar or kerosene and water, or in some cases at least it looks like possibly sometimes just kerosene. Women have their hair soaked and then they go through and shower and then they come out and they have these, these steamed clothes waiting for them. And it's pretty, it's a pretty humiliating process, but it's really all kind of based on we don't want this Mexican Laos coming across the border. And then like, if you really dig into the documents, you start to see that there is like, wartime stuff happening, the revolutions happening. And yes, typhus is much worse in Mexico because the revolution is happening concurrently. But again, it already exists in the United States. So, like, it. Crossing the border is not really a thing people should be worried about, I think, at this level. But, but, but literature about what to do for soldiers who are going down to the border, it basically says, like, the Mexican body louse causes this, like malignant typhus. In other words, like different than the one in the United States. But it's the same, right? And so we start to see treatment of Mexicans shift because of this bug that again, we already have here. And it is completely associated with Mexicans in Mexico. And there's not a lot of talk amongst public health officials during this outbreak or after about how it already existed well before this within US borders. That's my point, that these ideas about bugs and disease really start to shape the way that we treat people crossing the border from Mexico. And I should be clear, just Mexicans. There is a, a whole thing that says if an American crosses and read white American crosses the border and comes back into the United States, we can be sure that they will bathe and wash the louse down the drain. But we cannot be sure if a Mexican will do the same is one of the main things, one of the main refrains I should just keep with my rhyming scheme that one of the health officials says over and over.
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Stephen Haussman
So you're making the case in the book that the construction of the first border fences has an environmental history, but you also make the case that there's an important gender history here as well. How is the fence construction and how is this history gendered in really interesting and important ways too?
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Mary Mendoza
Yeah, so that's a great question. That is a good one to ask next because one of the things I haven't necessarily focused on with the bugs is the other thing with these, like, eradication campaigns is a lot of the literature focuses on the female lack louse or the female tick because of their capacity to reproduce in like, these massive numbers, thousands and thousands of eggs, thousands and thousands of tiny baby ticks that they can reproduce or, or Baby louse, baby body lice. And so it's sort of interesting that, like, the scientific journals don't really talk about the male, even though these bugs produce reproduce sexually. And I just sort of note that earlier on, as sort of a nugget to what's to come. And what's to come is women begin crossing the border during the Bracero program, which is a guest worker program that lasted from 1942 to 1964. And that program was open only to young, landless or poor men who were willing and healthy. So they had to continue those health examinations like the ones I just mentioned, with a little bit of differences, but that's not the point of this particular question. And it excluded all other men, and it excluded women. But increasingly, as I discovered, as I did research for this, I found women were trying to cross the border in larger and larger numbers as more and more braceros crossed the border, too. They were like, we want to go either because our husband is in the north working, or because we just want to do it ourselves. And so they were submitting paperwork to the Mexican government to try and get the Mexican government to support them. And there was kind of a technicality that allowed for some of that to happen, which I won't go into too much detail here. But the point is there is a record of these women trying to go. So I can sort of count the number of times women applied for this thing over a period of years. And what I see is a really big rise in that number. In the Mexican archives on the US Side of the border, I see the same, but in terms of Border Patrol agents complaining about the rising number of women, or women and children crossing the border. And so there's like, a really lovely correlation between the Mexican archive and the US archive in this period of, say, 1942 to 1956, it continues to go up. But this is like the biggest moment of complaining from Border Patrol agents and the biggest rise. And so before this, border fences and border kind of fortification projects really had only to do with bugs, disease, cattle, things like that, really more agricultural. There were a couple moments in the revolution that Rachel St. John writes about where we mark the border to make sure people are not crossing over during the war. But generally speaking, it is about agricultural concerns. In the 40s and the 50s, as more and more women cross the border, Border Patrol agents start to say, you know, these women are going to come and they're going to have babies, and those babies are going to be Mexican Americans. And if they have Mexican American babies of Poor moral values. Those people are going to then fill our prisons, and this is going to be really bad. And so at the time, anchor baby wasn't a term, but our border patrol agents were very aware of birthright citizenship and all of its implications, and they very much did not want women crossing the border. They also claimed that women were dirty and diseased and would spread venereal disease. Not at all taking any accountability for their behavior, say, if they were to get any of those diseases. But the point is that they were very, very concerned about women crossing. And so they said, you know, we keep apprehending women in places like Brownsville and places like Laredo. We would really love to build fences in these urban areas to stop this from happening, because when we do this, people in these cities are watching us apprehend these women, and they're shrieking and they're crying and they're screaming, and they're using their femininity to basically make us look bad. We look like monsters, and we don't want to do that. And so let's build some fences to push them to the desert where we can still chase them and apprehend them, but nobody will see. It'll be out of the public eye. And so we actually end up building the first border fences during the Bracero program because of unsanctioned migration, people migrating outside of the program. But the main people we're targeting in this situation is women, and we're focused on women because we don't want them to come here and have children. So there's a sort of reproductive through line in the book when it comes to, like, fearing that reproduction north of the border, whether it's the tick or the Laos. 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Mary Mendoza
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- [36:38]
Stephen Haussman
that really gets the ball rolling, so to speak, on the increasing criminalization of border crossing in the kind of mid to late 20th century. So why and what does it look like for border crossing to become criminalized in this era? And then how does the US respond to border crossings? And kind of as corollary to that, how does the American response differ from the Mexican response to border crossing in this period of time too?
- [37:06]
Mary Mendoza
Yeah, that's a great question. So at first. Okay, so during the Bracero program, I'll just do a quick overview here. It's a bilateral agreement, so both countries agree that they're going to send Mexican men north to work. As I already mentioned, there are people migrating outside of the program in large number. And what's important to note in this moment, and as Kelly Lytle Hernandez also notes in her book, both nations have a huge interest in regulating migration across the border. Mexico wants to regulate out migration because they want to maintain a strong labor force in their country. And the United States wants to regulate immigration because they don't want people coming outside of a regulated program and settling permanently in the United States and having babies. Right. And becoming part of US Society. And so it's in both of their interests to, to to regulate and enforce the border in this way. So they do. They do it together. Mexico actually creates a border patrol and the border patrol in Mexico works with the border patrol in the United States. And sometimes they're like radioing to each other, oh hey, I see people crossing, let's go help. And like they really Coordinate quite well at the beginning, but it does. And in fact, they even coordinate in the abuse of some of these migrants. So, like, and then again, this is in Kelly La Hernandez's book, but I do mention it in mine at one point to, like, mark repeat crossers, they were doing something called peeling, which is like a reference to scalping, but they would shave the heads of the men who came across so that they would know, oh, well, this person has a shaved head. They tried last week, right? They could recognize who had already crossed the border. And when American Border Patrol agents were questioned about that and essentially told to stop doing it for a while, the Mexican Border Patrol picked it right up and started doing it for them. And so, again, there's some real cooperation in the beginning. As time goes on, resources in Mexico are not as abundant. And the Border Patrol in Mexico complains about lack of resources. They say, oh, the Americans have a plane and they have horses and they have roads and they have all of this infrastructure, and we don't have that. And so we start to see in sort of the. The ways in which they talk about each other, the agents, this relationship begins to fracture. The US at one point, and this is not in the book, it's something I'm working on now. Started using dogs to patrol Mexicans. And Mexico didn't respond well to that because they were like, why are you terrorizing Mexican people with these animals who. Growling at them and chasing them down? Things start to go south for a whole bunch of reasons. But the general reason is resources in Mexico were not as abundant, and Border Patrol morale on the Mexican side just basically tanked. And so Border Patrol agents in the US Started to speak poorly of them, calling them lazy. And then some years go by, the Border Patrol ends. I'm sorry, not the Border Patrol. Excuse me, the bracero program ends. The Border Patrol did not end, and the Mexican one eventually does, but not the US One. And there's something called the Tortilla Curtain that happens, like, in the 70s, and the US decides it's going to build a fence because it's passed an immigration law in 1965 limiting the number of Mexican people and people from the entire Western Hemisphere who can cross the border in certain numbers. And it seems like migration, illegal, quote, unquote, illegal migration, continues to climb. And so they're like, we should do something. We've passed this law and it's not working. Let's build a fence. And so they build this border fence, which is now called by several the Tortilla Curtain, because a Local resident said that Mexicans were going to, quote, eat it up and by dismantling it almost as soon as it went up. And a contractor was interviewed who was going to build this fence in the United States. And he said, I'm going to build a fence so tall and so strong, it's going to sever the fingers and toes of anyone who tries to climb it. There's huge outcry in Mexico. The Mexican government gets really angry Mexican people, Mexican Americans, and the US President has to meet with the Mexican president to smooth things over and redo the design, which they do. But it becomes this huge point of tension where this sort of slowly kind of breaking relationship between the two nations vis a vis collaboration on migration really kind of just completely breaks off because Mexico is like, look, you have no reason. You don't seem to care about humanity and like, doing this in a humane way. You are, you are abusing our citizens and we can't stand to watch it. So we are not going to help anymore. And I argue that is a period, sort of late 50s into the late 70s, where the United States and Mexico kind of break off in terms of collaboration on migration. And it becomes a much more, not entirely, but a much more unilateral thing that the United States does. And then of course, we see years and years of, in the 80s and we see 1986 law, we see 1994 with NAFTA and President Bill Clinton building more Operation Gatekeeper fences, just big metal ones that push people into the desert. And it just gets worse and worse and worse and worse. And so we see today 780 something miles of fences now post secure act, post Trump, who actually didn't build that many miles. And things are getting harder. People are dying as they cross. And yeah, things have escalated.
- [43:29]
Stephen Haussman
And yet, and yet, despite all of these attempts at control, I mean, you just listed off a litany of laws and rules and regulations that have attempted to assert control over this region. People continue to defy this. What looks on a map like such a seemingly solid border. Control of the borderlands remains, you know, elusive on the part of the United States government. So I'm wondering, as we start to kind of approach the end of our conversation here, how has the region's environment in particular continued to kind of allow for people to defy the border, to continue to border cross? What effects have these attempted enforcements had on the region's environment? What's the kind of current environmental story and history there?
- [44:13]
Mary Mendoza
Well, it's so interesting about the. I won't Say the end, because this is like an ongoing issue, of course, but like the end of the story in the book at least, is that what we started out to do was to control nature, right, in a particular way. And by the end of the story, we are, we are controlling nature, but not the nature we intended to control in all kinds of bad ways. And so there's like local extinction risks for things like the jaguar or the Mexican gray wolf or bighorn sheep. Like, lots of animals that people in the United States and Mexico deeply value. And so we see like a lot of harm there. Plants all along the border are also at risk. Plants on the Tohono Odom Nation have been just desecrated in many ways. Burial sites have been desecrated there. And people also have died in increasing numbers as they've crossed the border. So there are now bodies, human remains out in the desert, sometimes found and sometimes never found, sort of just rotting in the sun, which is a terrible image, but it is a reality of what has happened with the construction of these fences. However, there are plenty of animals and people who continue to get across. There are still risks for Texas fever outbreaks in South Texas, and they happen sometimes. We have this issue with the screw worm, right? Bugs of various kinds are crossing the border. People always find a way because these fences, although, as you say, it looks like a solid kind of thing, based on some of the news we see, it really isn't. The border is 1,951 miles long and we have maybe 780 something miles of fences. So not half, I'm doing bad math, but yeah, not even half. So it's really not that closed off. What I think the US government relies on is environmental hazards. So they marry the built environment with the natural environment like the mountains and the really hot deserts to sort of hope that they will deter people from crossing these difficult spaces. But there is a lot of power in someone wanting to come to make a better life. And the same goes for animals. They are doing what they can to survive. And so there's a sort of innate thing that any living organism has to migrate to a place to get the things they need. And whether it's a person or a mosquito with Zika virus or a screw worm, they will find ways to cross unnatural boundaries for natural purposes.
- [47:23]
Stephen Haussman
Well, as we begin to wrap up here, I always like to ask my guests a question as sort of a summary question to get them to think about the book in maybe a different way. So instead of the person that wrote this book, I'd ask you to instead think of yourself as a reader of this book who turns the last page and closes the book and puts it back on their bookshelf three or five or ten years down the line. What would you hope that reader comes away remembering or thinking about this book after having read it and some time having passed?
- [47:57]
Mary Mendoza
I think my hope for this book has always been that a reader, whether it's a citizen in the United States in some random place that's going to go vote, or a policymaker, or just somebody across the globe who is also dealing with their own border issues, because there are many across the globe, puts it down and says, okay, I guess we need to think of a new solution because migration is natural and stopping it isn't going to work. So how else can we regulate migration? What else can we do to think about ways that allow for movement more humanely, that also doesn't kill the planet and harm nature in these really terrible ways? I think we're on a sort of repetitive treadmill or on like a. We're in a repetitive pattern of failure where something happens and we're like, oh, offense. And then we're like, well, maybe a law. And then back to offense. And then we, we repeat this cycle and we're still doing it. So I think maybe just the recognition that, that this hasn't worked for more than 100 years, really, even more than that, if we look at other places and maybe we should, maybe we should pivot.
- [49:29]
Stephen Haussman
You can't come away from this book without just kind of questioning the idea of borders as natural at all. This is a book that really makes you think about, as you kind of said, what are we even doing here? So it's very successful in that regard, I would say.
- [49:46]
Mary Mendoza
Yeah.
- [49:47]
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- [49:47]
Mary Mendoza
I mean, yes, the nation state does, I understand, need to regulate what comes across its boundaries, but really it's what I'm hoping is that we start to think about safer and better ways and more sustainable ways to do that going forward.
- [50:01]
Stephen Haussman
And then for my last question, Mary, I always like to get a glimpse or a preview of what my guests have been working on. Since this is a very recent book. It's been out for just like a matter of weeks at this point. But, you know, if I know historians, I would guess that you have a couple projects maybe percolating over there or things that you've been excited to start working on once this book is out. So is there anything you'd like to give us a little preview of any kind of works in progress you'd like to tell us about.
- [50:28]
Mary Mendoza
Thanks for asking. I have a couple of things I'm thinking about. One is something that really more comprehensively talks about the distinctions between borders and borderlands as two very different but very related things. I think about borders as more of like the state or some entity, depending on the period of time, trying to manage space and people and other things, and the borderlands as this space of defiance. And then the bigger project, the actual big next project is the project on the environmental history of policing Latinos in the United States. So I want to consider what happens from, say, the founding of the Texas Rangers to today when racial bias in the police force, whether that's the border patrol, the police state, the border patrol, or inland police officers in particular cities, collides with environmental injustice. So if a migrant is crossing the border and his or her body is already debilitated, what happens if a border agent decides to use brute force? Does that make it worse? The answer is yes. But let's look at the conditions that cause that and structural reasons why. If someone in a city lives in a neighborhood near a freeway and breathe in particulate matter regularly, what happens if they are held in a prone position as they're being arrested and they have asthma? Will they die from asphyxiation more quickly? Yes, the answer is yes. But I again want to examine the structural issues that allow for both that racial bias to consistently be there, as well as the environmental conditions, the varied, varied environmental conditions that Latinos are exposed to that make these things so profound in their lives and challenges.
- [52:39]
Stephen Haussman
That sounds like a fantastic project. And, you know, much, much like this book, it's the kind of book where it's, you know, at first blush, you might not think that something like policing would have an environmental history similar to how, you know, what would an environmental history of a border even really look like? But then the second that you think about it a little bit more, do some research, all sorts of stories open up. So I can't wait to read that project.
- [52:59]
Mary Mendoza
Thank you. Thank you so much.
- [53:00]
Stephen Haussman
Dr. Mary Menzoza is an assistant professor of history at Penn State University. Her new book is Deadly How Insects, Pathogens and People Defied the US Mar Mexico Border, which came out with the University of North Carolina Press just a few weeks ago here in June of 2026. Thank you so much for joining me today.
- [53:19]
Mary Mendoza
Mary thank you so much for having me.
- [53:21]
Podcast Host
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