You’re driving down Highway 109 or Highway 350 in late August. The heat is still shimmering off the asphalt. Suddenly, you see a dark shape scuttle across the road. Then another. And five more. Most people freak out. They think it’s an invasion. But honestly? It’s just a bunch of lonely guys looking for love in the high desert of Southeast Colorado.
The La Junta tarantula migration isn't actually a migration in the traditional sense. Birds migrate to find food or warmer weather. These spiders—specifically the Aphonopelma hentzi, or the Texas Brown Tarantula—are on a different mission. They’ve spent nearly a decade underground, waiting. Now, the males are finally venturing out to find a mate before the first freeze hits.
It is a desperate, one-way trip.
The biology of a "Migration" that isn't one
Let’s get the terminology right. Biologists like Dallas Haselhuhn, who has studied these arachnids extensively, often prefer the term "mate-searching" over "migration." When you see hundreds of tarantulas moving across the Comanche National Grassland, you are looking at a bachelor party of epic proportions.
The males reach sexual maturity around age 8 or 10. That’s a long time to wait. Once they hit that milestone, their internal clock starts ticking loudly. They leave their burrows, often for the first and last time. They aren't moving toward a specific geographic location like Mexico; they are just roaming the plains, following the pheromone trails of females who are tucked away safely in their own silk-lined homes.
Female tarantulas are the homebodies of the spider world. They can live for 20 or even 30 years. They rarely leave their burrows. While the males are out dodging tires and hawks, the females are basically waiting for a "knock" on the door.
Why La Junta?
The geography matters. The Comanche National Grassland offers a massive, relatively undisturbed expanse of shortgrass prairie. This is the ideal real estate for A. hentzi. The soil is right for digging, and the prey—mostly grasshoppers and other crunchy insects—is plentiful.
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It’s also about the weather.
Timing is everything. Typically, the activity peaks from late August through September. If it’s a particularly dry year, you might see fewer of them. If we get a nice late-summer rain, the humidity seems to kick the males into high gear. They don't like the scorching midday sun, so they usually wait until about an hour or two before sunset to start their trek.
What it’s actually like on the ground
If you go down there expecting a scene from a horror movie where the ground is moving, you’re going to be disappointed. It's more subtle. You’ll be driving, and you’ll spot a movement. You pull over. You realize there’s one every fifty feet.
They are remarkably docile.
Texas Browns aren't aggressive. They don’t jump at you. They don’t have "deadly" venom—at least not to humans. Most experts compare a tarantula bite to a bee sting. Unless you have a specific allergy, it’s just a localized ache. Their real defense mechanism is actually their "urticating hairs." If they feel threatened, they use their back legs to flick tiny, barbed hairs from their abdomen. These hairs are incredibly irritating to the skin and eyes of predators like coyotes or curious dogs.
But mostly, they just want to keep walking. They have a job to do.
The gauntlet they run
It is a dangerous time to be a male spider in Otero County.
Road mortality is the biggest threat. Thousands of these guys end up as smears on the pavement because they happen to be crossing Highway 109 at dusk. Then there are the Tarantula Hawks. These aren't birds; they are massive wasps with iridescent blue-black bodies and bright orange wings.
The Tarantula Hawk is the stuff of nightmares. A female wasp will sting the tarantula, paralyzing it instantly. She then drags the limp spider into a burrow, lays a single egg on its abdomen, and seals the entrance. When the larva hatches, it eats the spider alive, saving the vital organs for last to keep the meal "fresh" as long as possible.
Nature is pretty brutal.
Tips for a successful spider-watching trip
Don’t just wing it. If you drive down from Denver or Colorado Springs without a plan, you might miss the window entirely.
1. Watch the clock.
The best viewing window is usually between 5:30 PM and 7:30 PM. As the shadows lengthen, the spiders emerge. Once the sun is fully down, they become much harder to spot against the dark soil and pavement.
2. Check the map.
The "Tarantula Triangle" is roughly the area between La Junta, Pritchett, and Las Animas. Specifically, Highway 109 south of La Junta leading into the Comanche National Grassland is the "Goldilocks zone."
3. Respect the property.
A lot of the land surrounding the highways is private ranch land. Stay on the public road shoulders or stick to the designated areas within the Comanche National Grassland.
4. Leave them be.
It is tempting to pick one up for a photo. Try to resist. These males are already under incredible stress. They aren't eating much, they’re dehydrated, and they are burning their final reserves of energy to find a mate. Moving them or stressing them out just makes it harder for them to finish their life's work.
Misconceptions and weird facts
People think the tarantulas are "coming for them." They aren't. In fact, if you stand still, a tarantula might walk right over your boot without even realizing you’re a living thing. They have terrible eyesight. They mostly navigate through vibrations and chemical cues.
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Another weird thing? The "mating dance." When a male finds a female's burrow, he doesn't just barge in. He taps on the silk at the entrance. It’s a specific rhythm. If the female is interested, she comes to the entrance. The male then has to use special hooks on his front legs (called tibial spurs) to hold her fangs back so she doesn't eat him during the process.
Even if he survives the mating, the male tarantula usually dies shortly after the season ends. The cold of the first frost is usually the final curtain call.
The economic impact on Otero County
Believe it or not, the La Junta tarantula migration has become a legitimate tourism draw. For a long time, the locals just thought of it as "that time of year when the spiders are out." Now, people fly in from all over the country.
The city of La Junta has embraced it. They have a "Tarantula Fest" now. It’s a mix of educational seminars, guided tours, and community celebration. It’s a great example of how a town can take something that people are traditionally afraid of and turn it into a point of pride and a source of revenue.
Businesses like the Bent's Old Fort National Historic Site or local diners see a noticeable bump in foot traffic during September. It's a weird niche, but it works.
Navigating the ethics of wildlife viewing
As this event grows in popularity on social media, there is a rising concern about the impact of "influencer" culture on the spiders. You'll see videos of people corralling a dozen spiders into one spot for a "cool" shot.
Don't be that person.
The ecosystem here is fragile. The shortgrass prairie takes a long time to recover from heavy foot traffic, and the spiders themselves are sensitive to handling. If you want to take pictures, use a zoom lens. Let them cross the road at their own pace. If you see one in the middle of a high-traffic area, you can gently nudge it toward the shoulder in the direction it was already heading, but otherwise, let nature take its course.
The reality is that we are lucky to have this. In many parts of the world, large arachnid populations are crashing due to habitat loss or the pet trade. The fact that Southeast Colorado still has a healthy enough population to create this "migration" is a sign that the Comanche National Grassland is doing its job.
What to do if you’re heading down this year
If you are planning a trip, keep your expectations realistic. It’s not a parade. It’s a wildlife encounter.
- Pack layers: The high desert drops in temperature fast once the sun goes down.
- Gas up: Once you head south of La Junta on Highway 109, services are few and far between.
- Bring a good flashlight: Not just for seeing spiders, but for making sure you aren't stepping on a rattlesnake, which also enjoy the evening warmth of the pavement.
- Check the weather: A heavy thunderstorm will wash out the "migration" for the night. You want a clear, calm evening.
Honestly, the best part of the whole experience isn't even the spiders—it’s the sunset over the canyons. The sky turns colors you didn't think were real, and the silence of the grasslands is something you don't get in the city. The tarantulas are just the weird, fuzzy guests of honor at a much larger party.
Actionable steps for your visit
If you want to contribute to the science, consider using the iNaturalist app while you're there. Scientists use the data points from citizen scientists to track the health and movement of the A. hentzi population.
Take a photo (from a distance), upload the location, and you’re officially helping lepidopterists and arachnologists map out the future of these creatures.
Stop by the La Junta Visitor Center first. They usually have the most up-to-date info on where the "hot spots" are for the current week. The spiders move depending on the year's moisture and temperature, so a spot that was crawling with them last Tuesday might be empty this Wednesday.
Support local. Eat at the small diners in La Junta. Stay at the local motels. The more the community sees that people value the spiders, the more they will work to protect the habitat that makes this whole phenomenon possible.
One last thing: check your shoes before you put them on if you've left them outside your tent or hotel room. Not because the spiders are out to get you, but because a dark, warm boot looks an awful lot like a nice place to hide from a Tarantula Hawk.
The La Junta tarantula migration is a reminder that the world is still a bit wild, a bit strange, and definitely worth a long drive into the middle of nowhere. Just watch where you step.