As one would expect with any good horror flick, these antagonists prefer to emerge when the light fades. They crawl up out of their burrows, their furry, brown bodies barely rustling the prairie grasses as their legs (all eight of them) pad lightly across the soil. They’re on the prowl—but not with any malevolent intentions. In fact, arachnid experts from Westminster–based Butterfly Pavilion, which has focused on tarantula research since 2010, say the creatures are relatively harmless. They’re just a bunch of bachelors looking for The One.
Each September and October, when the nights in Southeastern Colorado turn chilly (but before hard freezes begin), male Oklahoma brown tarantulas begin their quest for love. They’ll amble around 20 to 100 meters each evening to find it. More and more, visitors are heading to the spiders’ neck of the grasslands to watch. “It’s becoming a big deal,” says Lorna McCallister, former target species manager at Butterfly Pavilion. “It’s a very cool ecological thing that’s turning into a tourism opportunity.”
Dubbed a “mategration” (it’s not technically a migration since there isn’t persistent movement or a significant relocation to a new habitat, McCallister says), the journey is a long time coming for these spiders: It generally takes males between seven and 10 years and females 10 to 12 years to reach reproductive readiness. By then, the spiders have grown to roughly 5 inches in diameter, and the males have finally grown pedipalps, a pair of appendages attached to their head.
Come fall, the of-age males wander around in search of a female’s burrow. Upon finding one, he will stand outside and drum his pedipalps. If the female is a willing partner, she’ll crawl to the surface, and the male will hold her up above him so that they’re facing each other. It’s a quick coupling—and for good reason. “He tries to get in there, mate, and get out without being eaten,” McCallister says, adding that roughly one-third of female tarantulas strike at their mates and around 20 percent actually kill them, which is not necessarily retribution for poor performance. “If you’re a female, and you know you’re about to raise a hundred-something babies, you’re probably going to take whatever meal you can get.”
Yet even males that do escape their partners’ clutches have numbered days. “Within about a year of doing the [odyssey] and mating, they die,” McCallister says. “That’s basically the last hurrah of their life.”
Tarantulas eat primarily beetles, grasshoppers, crickets, and other small insects, while dodging becoming a meal themselves for coyotes, foxes, snakes, some birds, and 2-inch-long tarantula hawks, a nasty breed of wasp that lays an egg in the tarantula’s abdomen so the larvae can eat the living host as they grow.
There’s still a lot to learn about these eight-legged creatures. Just this year, the Butterfly Pavilion began a joint study with Colorado State University and the Southern Plains Land Trust to study the species’ hemolymph (essentially its blood). This research should help uncover how these arachnids survive subfreezing temperatures in southeastern Colorado, since most invertebrates struggle to move even when it’s 40 degrees outside. Researchers also hope to learn about changes in the Oklahoma browns’ metabolisms over their lifespan and build a sort of “family tree” of Colorado’s native population.
Arachnologists are also just starting to understand what their burrows look like after Jackie Billotte, a doctoral candidate at Colorado State University who works with Butterfly Pavilion, took what’s believed to be the first-ever plaster molds of Oklahoma browns’ homes. “Spiders, including tarantulas, tend to be misunderstood and understudied,” Billotte says. “Public interest is important to encouraging increased research and getting the message out about the importance of the tarantulas to their ecosystems and how they can serve as a source of ecotourism for the nearby cities.”
That interest seems to be growing. Officials at Comanche National Grassland offer anecdotal evidence that there’s more traffic through their region during the tarantula mating season and an uptick in calls for information regarding how, where, and when to see the spiders.
The town of La Junta in southeastern Colorado has been promoting what it refers to as the Tarantula Trek since 2018 and added a Tarantula Fest to the lineup in 2022. Visitors attended from as far away as Vancouver, Canada. “The tarantula trek is an unexpected adventure for people to experience,” says Pamela Denahy, director of tourism for Visit La Junta. “We’ve definitely seen the tourism draw and the economic impact that tarantula tourism has had for our community.”
But all that traffic does pose a threat to the Colorado crawlers because vehicles run over hundreds of tarantulas attempting to cross highways. To combat this, the Butterfly Pavilion is studying where most crossings take place so the Colorado Department of Transportation can look into building tunnels below the freeway for these adventurous arachnids.
McCallister sees events like the festival, and tarantula-related tourism in general, as beneficial for all parties involved, no matter how many legs they have. “Public interest and support [are] vital for the success of conservation efforts,” she says. “It is crucial that we utilize opportunities like ecotourism during the mategration as educational tools to spread awareness about the importance of tarantulas, their roles in our ecosystem, and why we should care about researching and conserving this unique species.”
Tarantulas in Colorado have a bit of a mythical status, with many rumors and misconceptions surrounding these eight-legged creatures. While some view them as scary or dangerous, tarantulas are a unique part of Colorado’s ecosystem and their annual migration is a fascinating natural phenomenon. This article will break down key facts about Colorado’s tarantula population, migration patterns, viewing tips, and how to safely coexist with these hairy spiders if you happen to encounter one.
Tarantula Species in Colorado
There are 5 species of tarantulas that are known to inhabit Colorado:
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Oklahoma brown tarantula (Aphonopelma hentzi) – This is the most common species spotted during migrations. They have brown bodies with faint banding on their legs.
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Colorado chocolate brown tarantula (Aphonopelma echinum) – A bit rarer than the Oklahoma brown, they are darker chocolate brown in color.
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Grand Canyon black tarantula (Aphonopelma marxi) – All black in color and somewhat uncommon
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Texas tan tarantula (Aphonopelma anax) – Light tan color with faint leg banding Rarely spotted
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Colorado blond tarantula (Aphonopelma vogelae) – Light blond/brown color and infrequently seen.
The Oklahoma brown is by far the most prevalent, making up an estimated 90% of tarantula sightings in the state. All of Colorado’s tarantulas are medium to large in size with leg spans reaching 3-5 inches. They are plump hairy, and easily identifiable by their large size.
Tarantula Habits and Lifecycle
Tarantulas are solitary, nocturnal creatures that spend most of their lives in individual burrows dug into the ground. The burrows provide protection from predators and unfavorable environmental conditions.
Females rarely venture far from their burrows, while males leave in search of mates during the late summer/early fall breeding season. After mating, the males soon die while females can live over a decade.
Sexual maturity takes 5-7 years and females produce eggs sacs containing up to 1000 baby spiders. The young emerge in early summer and strike out to dig their own burrows nearby.
Tarantulas are sit-and-wait predators, lying in wait to ambush insects, spiders, lizards, mice, and other small prey that pass by their burrow entrance. They detect prey through vibration and pounce when it’s within reach.
The Tarantula Migration Phenomenon
What really grabs attention is the annual tarantula migrations that occur in late summer/early fall (August-October).
As mating season approaches, hundreds of male tarantulas emerge from their underground burrows and embark on a perilous journey in search of females. They wander far, sometimes covering several miles over open plains and grasslands under the cover of darkness.
While a few isolated sightings occur elsewhere, the migration hotspots are in Colorado’s southeastern plains, especially around Comanche National Grassland near La Junta.
Peak activity occurs on warm evenings in September/October near sundown when the males begin to emerge. After finding a mate, the males either continue roaming or perish soon after.
Seeing scores of large spiders crossing roads and fields on their nightly trek is a unique sight and has become a popular wildlife spectacle. However, their cross-state walk is not without hazards ranging from predators to vehicles, making the journey treacherous.
Viewing the Migration Safely
Viewing the tarantula migration is a one-of-a-kind experience, but should be done safely to avoid disturbing the spiders’ natural patterns. Here are some tips:
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Time it around dusk when they start moving, especially in September.
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Bring flashlights or headlamps so you can spot them better in the dark.
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Pull off roads fully and watch for traffic when viewing or photographing.
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Keep distance and don’t touch or handle them.
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Walk carefully and avoid stepping on burrow holes.
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Never dig up or disturb their burrows.
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Don’t impede their path across roads or fields.
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Avoid using flash photography and bright lights.
Remaining quiet, patient, and observant from a slight distance will allow you to witness their amazing journey without interference.
Are Tarantulas Dangerous? Tips for Safely Coexisting
Though intimidating in appearance, Colorado’s tarantulas are not aggressive toward humans and rarely bite unless severely provoked or handled.
Their venom is mild compared to other spiders and only causes localized pain, swelling, and irritation around the bite. Serious reactions are very uncommon.
Here are some tips for safely coexisting if you encounter a tarantula around your home:
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Remain calm and move slowly to avoid startling it.
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Gently coax it into a container using gloves or an object.
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Release it outside away from high traffic areas and burrows.
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Seal gaps around home exterior to discourage entry.
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Keep pets indoors if tarantulas are active near home.
While startling if seen indoors, tarantulas are important members of Colorado’s ecosystems. Their migration is a unique natural wonder providing an opportunity to observe nature at work. By understanding their habits, viewing them safely, and using care if encountered around the home, we can appreciate these docile giants of the spider world.
Ready to Go Spider Spotting?
Here are McCallister’s top tips for spying tarantulas this fall.
- Though the spiders are often easy to spot as they scuttle across major roadways south of La Junta like CO 109 and U.S. 350, try to go elsewhere if possible. Comanche National Grassland, for example, offers plenty of opportunity for sightings without the danger of semi-trucks barreling along nearby.
- Start looking around dusk when the male tarantulas are most active, but it’s still light enough outside to watch them moving around without a headlamp.
- Be content with seeing a handful (or even just one or two) tarantulas. “It’s not like the wildebeest migration where you see thousands at once,” McCallister says.
- Oklahoma browns are quite docile. They move slowly, and their bite is relatively harmless (unless you’re allergic). Still, it’s not a good idea to pick them up. Not only is it stressful for the spider, but they have urticating hairs, which have small barbs that can get stuck in human skin. “Getting haired by a tarantula is an itchy, not-fun experience,” Billotte says.
- If you can’t make it down to southeastern Colorado to see the males hunting for mates, head to Butterfly Pavilion instead. Its Spiders Around the World exhibition, which runs through October 31, features six-eyed sand spiders, the Amazon blue bloom tarantula, and hundreds of free-roaming orb-weaver spiders—some as big as your hand.
Lace up your hiking boots, head to La Junta, and keep your eyes on the ground. It’s time to track down some tarantulas.
Thousands of tarantulas migrating across Colorado roads
FAQ
Are there any tarantulas in Colorado?
Each September and October, when the nights in Southeastern Colorado turn chilly (but before hard freezes begin), male Oklahoma brown tarantulas begin their quest for love. They’ll amble around 20 to 100 meters each evening to find it.
What is the largest spider in Colorado?
Wolf spiders, among the largest spiders found in Colorado, are often mistaken as tarantulas. These beneficial spiders are foraging hunters that do not spin a web to capture food.
Where is the tarantula Festival in Colorado?
It’s a sight to see or avoid – depending on how much arachnophobia you have. Lately, this once little-known annual occurrence has been gaining national attention giving locals and tourists a new reason to explore La Junta, Colorado.
What month are tarantulas most active?
For tarantulas, the urge and need to mate come in the fall and they become most active during the months of September and October. Of course, there are variations year after year and sometimes they come out earlier or later than other times. Tarantula males are the one who goes out looking for mates.