The Audit Podcast: Don’t call it a ‘migration,’ Colorado’s tarantulas go on walkabouts


Welcome to Colorado State University’s new podcast, The Audit, featuring conversations with CSU faculty on everything from research to current events. Just as auditing a class provides a fun way to explore a new subject or field, The Audit allows listeners to explore the latest works from the experts at CSU. 

It’s that time of year again, when thousands of eight legged arachnids come out of their southeastern Colorado hiding places, looking for love. 

Despite often being referenced as the annual tarantula “migration,” the spiders aren’t actually traveling through, they’re year-round residents. They’re just much more visible during the late summer and early fall mating season. 

Audit host Stacy Nick spoke with Maia Holmes, an entomologist with the College of Agricultural Sciences’ Department of Agricultural Biology and director of Colorado State University’s hands-on traveling insect exhibit, the Bug Zoo, to find out a little more about this annual mating trek. 

This transcription has been lightly edited for clarity.

For folks who don’t know what we’re talking about, can you explain just a little bit about Colorado’s annual tarantula migration? The phrase does conjure up images of millions of spiders charging across the landscape, but I’m guessing that’s not the case.

Maia Holmes
CSU Entomologist and Director of the Bug Zoo Maia Holmes poses with Edith, an Oklahoma Brown tarantula. Photo by Stacy Nick/CSU

No, fortunately or unfortunately, depending on who you are. A migration is usually when every animal in a species gets up, goes somewhere, does something, and comes back. But tarantulas aren’t doing that at all. We call it a walkabout because it’s only the males. The males mature at a different rate than the females, at around 8 to 10 years old. Then they’ll start walking about, looking for the burrows of females. 

They’ll come up onto a female’s burrow, and they can tell that there’s a female of the same species in there based on smell. They’ll do a special little knock with these really cool things called pedipalps, which are mouthparts, but reproductive mouthparts. They’ll do the special knock, and the females will come out and either be like, “Yes, I would like to mate.” Or “actually I’m hungry and I’m going to eat you.” Or sometimes both. It’s just the males that are traveling who are mature, and most of them don’t make it much longer after they mate. The females can hold on to that sperm and they’ll have a nice little clutch of 1,500 babies whenever the environment’s good. They can hold on to that for a while. 

We see it this time of year because it’s when the males are maturing and when the weather is right for them to be able to get up and look around for females. They can travel up to a kilometer, which is not that far for a human, but really far for something that’s as small as they are. It’s like running a marathon. 

When you say “knocking,” I’m imagining it’s like (knocks on table)

Kind of, yeah. Their pedipalps are almost like little legs. When males mature, the pedipalps become hollow and act almost like a turkey baster. They’ll lay their sperm on a web and then turkey baster it up into their pedipalps. Then they’ll use those pedipalps to tap out a rhythm. In some spiders it’s an extremely specific rhythm, so they like drum or sing to each other, and that’s how females determine if the male is good or not. They have to be good drummers. Spiders dig drummers. That’s how they’re communicating that they’re ready to mate, and that they’re not just some regular old prey. They’re hopefully prey, but with sex, too.

It’s literally their serenade.

It’s more like a candy gram almost, where they’re on the other side of the door and that’s to get you to open the door. The females usually will come out. Cannibalism in tarantulas is not as prevalent as it is in other arthropods, but it definitely can happen because a female has to produce 1,500 eggs. So, any extra meal counts.

Girl’s gotta eat.

Yeah, it’s a lot to produce.

How many tarantulas do we see in a typical mating season?

That’s actually something that I’m concerned about because about 30 years ago, you could go out and multiple nights you’d see hundreds of tarantulas. And over the last several decades, we’ve been seeing an extremely alarming decline in the number of tarantulas out there. Now if you go out, 10 in a night would be a phenomenal night. So, there are still a lot out there. There are probably hundreds. But we are seeing a lot of decline in our tarantula populations, likely due to climate change.

They are popular for tourists to go visit. Is that a good thing or is that maybe not so good for people who want to go check these guys out?

Ooh, that’s a complicated question and a complicated answer. I think it’s probably a little bit of both. It’s really good for people to get excited and people to see tarantulas as something that’s a really cool thing in nature. Like, we have tarantulas in Colorado. That’s so cool. It’s less cool if it means that people are going and finding them and taking them out of the wild. So, it’s good to observe them in a way that is very conscientious that they’re a wild animal in a wild place.

Is that a big problem? Are there poachers that go out during this time and try and find tarantulas?

It’s not legal to sell native animals in Colorado. There’s not really a financial incentive to do that. But elsewhere in the world, tarantula populations are absolutely being affected by people going out and collecting them and then selling them into the pet trade. The tarantula pet trade has quadrupled, if not more, in the last 10 years. Ten, 15 years ago, you could get maybe five different kinds of tarantulas. Now I go into an exotic pet store, and I don’t know what most of the tarantulas are. I’ve never seen them before, which means we aren’t recording how many we’re taking from the wild. We don’t know what proportions are being taken out of the wild. So, if you’re taking a hundred, but there’s only 150, that’s really bad. And we’re actually seeing a lot of tarantulas ending up on protected lists now, too.

Where’s the best place for people to see the tarantulas?

Their habitat is the grassland areas of southern Colorado, particularly around the Pueblo area. La Junta’s a pretty popular place this time of year, too. It’s actually starting to see a little spike in tourism this time of year because of the tarantulas. But any of those southern-most grassland areas are great, especially if you want to do a weekend camping trip. You can see them there.

When is the best time of year and best time of the day?

Tarantula finding is great for night owls, so if you’re getting up early in the morning, it’s too cold. They need the temperature to still be warm, but not cold yet. You’re going to see them mostly when it’s starting to get dark and cooling off, like eight at night up until about one in the morning. And the easiest place to find them is by road cruising. Drive around on the little back roads in the areas and watch them cross over the streets. The more populated an area is, the less likely you are to see them because they need burrows and human dwellings don’t really allow for burrows.

And there’s a timeframe here, right? We’re coming right into the prime season. How long does it last?

The peak of it really depends on the temperature, but usually mid-to-late September and then maybe a couple weeks around that. By October it’s usually too late, it’s too cold at night for them.

I want to go back to something you were talking about with the roads, you want to keep an eye out for them, obviously. And I know there’s a movement to try to maybe make an overpass or something for them to protect them.

I know that they do that for other wildlife. There has been mixed research on the effectiveness of those because predators like to hang out on those overpasses. So, prey animals sometimes are hesitant to use them. It doesn’t actually end up helping as much. They’ll still prefer the road to a bridge or a tunnel. With tarantulas, it’s not so much that they’re preferentially picking roads, it’s that they are going to move, and roads are in the way. And so, they’re crossing the roads and then just getting splatted. So fortunately, there’s a lot less traffic in the middle of grasslands. But it is still something to look for. If you see a tarantula, don’t hit it. And again, we aren’t seeing numbers where an entire road is going to be covered by tarantulas. In a mile stretch, you’ll see maybe eight.

So, obviously cars are not great for tarantulas, but what other kinds of things are tarantulas dealing with right now? What predators are out there?

Tarantulas are tasty food for many things, including humans. There are several different groups of people who will eat tarantulas. I hear it tastes a lot like lobster because they’re very closely related. I’ve never eaten a tarantula because I’d feel bad about eating a tarantula. 

There’s actually a very specific type of wasp called a tarantula hawk wasp. They’re rather big wasps, and they’re called parasitoid wasps. They can smell the tarantula from a distance using pheromones. They’ll sting the tarantula and paralyze it and then drag it down into a hole and lay an egg on it and seal it up. And then the egg hatches and eats the tarantula alive. So, I’m really glad we don’t have any parasitic wasps that parasitize humans, yet. Evolution is pretty good at coming up with new ones. 

There’s also birds and coyotes. Coyotes love to eat tarantulas. House cats will also go after tarantulas in areas where there are feral or even somebody’s outdoor cats. 

Tarantulas do have this defense mechanism called urticating hairs, which are these special hairs that are like fiberglass. Itchy, prickly — like cacti. Kind of like if you’ve ever had the misfortune of rolling in insulation fiber. They’ll flick those off in a cloud at whatever they feel threatened by. But once they run out of those hairs, they don’t have any more. Tarantulas that have used up those hairs on encounters with one or two other predators, by the third predator, they’re kind of defenseless. And the wasps are immune to the hairs. A ton of things eat tarantulas.

It’s a rough life.

Yeah, it’s tough. It takes females about 15 years to become mature, but they can live for 40 years. Then males take eight to 10 years. And they don’t usually make it for more than two years post-maturity in captivity. In the wild, they’re usually gone before the first frost.

Now, you have a little guest here with us. Who do we have here?

Yeah, I brought Edith. She is one of our Oklahoma Browns, which is our native species here, Aphonopelma hentzi. I brought her so we could describe her a little bit for people who are listening. Oklahoma Browns are kind of a weird name because common names aren’t super helpful. She is found in Oklahoma, but she’s also found in a lot of states. That’s actually the most common tarantula in North America. They can be from Louisiana across to California and then again down from the Louisiana and Texas area. Colorado is about as far north as they get. They’re called an Oklahoma Brown or a Texas Brown or a Texas Tan or Burrowing Brown. They are brown. I think they’re a beautiful brown. Their head is like a milk chocolate brown. And then their body can be like a deep chocolate to almost black velvet when they molt. I think they’re a really striking tarantula. A lot of people think they’re boring because they’re brown, but I think they’re phenomenal.

She is a beauty. Where did you get her from?

This is actually one of the ones that was given to me when we filmed an episode of “Deep Look” through PBS and KQED. The filming crew went out to film them in their native habitat, and they were actually able to find a couple of females that were out, and they collected them and brought them with them. We were able to film them in the studio so we could create that episode. Then at the end by the time we finished filming everything for that episode, it was too cold to rerelease them back to where they had been. And you usually don’t want to rerelease animals if they’ve been in captivity for too long. Edith, Caroline and Bernice are our three females. And then the males that they also brought with them. They got to have their 15 minutes of fame on PBS. They did eventually die because they don’t live nearly as long. But we’ve got probably several more years with all of our females.

Edith, you’re a celebrity.

I don’t think Edith was actually one of the ones that got filmed because she’s a little bit more cantankerous than our other ones who are more willing to be manipulated under lights and everything like that. But she does okay on outreaches.

That’s really cool. I had no idea how they do that process. I watched the video, and it was amazing. Whenever you see those kinds of nature programing, you always wonder how they got that shot. So, there’s maybe a little Hollywood magic happening there.

Could you tell which ones were shot in the wild and which ones are shot in the studio? 

Not at all.

It was all macro photography and we filmed for about oh, it felt like a week, but it was probably three or four days of constant filming. Of course, animals never act the way you want them to act when a camera’s running, and so we had to redo it over and over again. I had to switch between the four different tarantulas because females don’t want to mate back to back to back but the males were ready to go. Luckily, I had enough males that also were willing to pair up enough that we got the shots. There’s a lot of unused footage that was just a tarantula sitting there not doing anything.

How did you get connected with that project?

Elliott Kennerson, the editor for “Deep Look,” had just moved to Boulder and was looking to do some sort of entomology-themed thing that wasn’t based out of California. He just did a quick Google search and the Bug Zoo showed up. He sent me an email asking if I would be interested, not knowing that I was a “Deep Look” super fan and had watched every single episode that had ever existed.

If anyone heard that deep breath that I just took. Edith just moved up the wall of her open enclosure for a second and startled me just a little bit. Not a lot. 

They’re slow moving and totally harmless. Really the worst you could do is get itchy, even if she bit you and used her venom. Humans don’t react to their venom. 

There’s this perception that especially tarantulas are very dangerous. That they attack, that they are something that people are rightfully afraid of. But as you just mentioned, they’re not really harmful.

Like almost all spiders, tarantulas are not nearly as dangerous as they’ve been portrayed. There isn’t any record anywhere of someone dying from a tarantula bite. In North American species, they do have those itchy hairs. Those urticating hairs, which means that their venom is a lot less potent because they’re depending primarily on having you get away from them with those itchy hairs. They’re absolutely lethal if you’re a cricket or a cockroach or any of their prey. But they don’t eat mammals, so mammals don’t really react to their venom because their venom is primarily there to help them eat. Other tarantulas do have more potent venom from places like Asia and Africa because they don’t have those hairs. They depend on their venom more for defense. So, they have venom that will ruin your weekend but won’t necessarily kill you. And then spiders in general, there’s thousands and thousands of species of spider out there. I would say that two are actually dangerous; one of them lives in Brazil and one of them lives in Sydney, Australia. So, it’s unlikely that you’d have to interact with them and be genuinely in danger from being around them.

So, that movie Arachnophobia kind of lied to us a little bit. 

I, like many entomologists I’m sure, have a complicated relationship with Arachnophobia because it’s objectively an amazing movie, it’s so good. And they used real spiders. I spent three days filming a five-minute video for KQED, and that’s a feature length film. The tarantula wrangling on that film is outstanding. But it also made people afraid of spiders because they used real spiders. And the main villain spider is not a real spider, but it’s so much fun to play with fear. It’s really fun to scare each other in safe ways instead of saying, “Oh, this is something that I have to really be afraid of.” Think of it more like a haunted house experience and less like an actual dangerous experience because spiders are not actually dangerous to humans. I don’t think there’s a spider out there that I would squish.

About The Audit 

Recorded at the KCSU studios, Colorado State University’s new podcast, The Audit, features conversations with CSU faculty on everything from research to current events. Just as auditing a class provides a fun way to explore a new subject or field, The Audit allows listeners to explore the latest works from the experts at CSU.