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As the sun sets behind the Rocky Mountains and cooler air settles around the state, Colorado's tarantulas will creep out of their burrows on the southeastern plains in search for love, an annual affair sometimes called a tarantula "migration."
It’s not quite a Romeo and Juliet love story, but every year, these creatures lure arachnid aficionados from near and far to the see the spectacle in person.
First, it's important to understand what this "migration" really is — and why we say it in quotes. It's not quite accurate to call tarantulas' movements a migration, as they are just more visible than other times of the year. They actually live in Colorado year-round.
Instead, you can call it a walkabout, said Maia Holmes, an entomologist with the College of Agricultural Sciences’ Department of Agricultural Biology. She was interviewed about the creatures on Colorado State University’s new podcast, "The Audit."
Beginning around the start of September, male tarantulas in the southern and southeastern part of the state will leave the safety of their burrows to search for females, which stay hidden in their own holes. They can wander for up to a kilometer — not much for a human, but pretty far for an arachnid, Holmes said.
When a male finds a female’s burrow, they drum their legs at the entrance — "Spiders dig drummers," Holmes said — and wait for the female to come out to breed.
"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," Holmes said.
The males don't live long after mating, if they survive the encounter. Death by predator, car or starvation — or rather, lack of interest in eating anything — typically follows.
This "migration" sets in once temperatures start to cool at night. It will continue until early October or whenever hard freezes begin.
The tarantulas are all around the eastern plains, particularly the southeastern region, though "mini" tarantulas also live on the western side of the state in areas like Montezuma, Montrose, and San Miguel, according to Colorado State University's College of Cultural Sciences.
All of the tarantulas that call Colorado home fall under the genus Aphonopelma, and they're all brown to camouflage into their environment. Their bodies, excluding their legs, are typically two to three inches long. The male tarantulas — the ones that "migrate" — are longer, with a small abdomen and long, spindly legs to help them get around quickly. The females, on the other hand, don’t need that kind of biological adaptation and are often larger.
Male tarantulas are sexually mature once they reach about 7 years old, and can live for about a decade. Females can live well beyond that — up to 40 years, Holmes said.
Interested in seeing wild tarantulas for yourself? There's a few things to know beforehand.
One of the best places to go to see the tarantulas is the Comanche National Grassland near La Junta and Springfield, about a three- to four-hour drive southeast of Denver. The scrubby grassland, which is a lower altitude compared to the Front Range, contains more than 400,000 acres for recreating, said Michelle Stevens, recreation program manager for the grassland.
She said drivers often see tarantulas crossing the road because they’re easy to pick out on the pavement. She recommends driving on Highway 350 between La Junta and Trinidad, or Highway 109 between La Junta and the town of Kim to see them.
Be prepared to head out around sunset and stay late into the evening (but be aware of the lines between public and private property). Most tarantulas will head back into their warm burrows around 1 a.m., when it starts to get too chilly outside.
Keep in mind these creatures are much more afraid of you than you are of them.
Despite common misconceptions, they’re not aggressive animals and won’t jump or attack a person.
Their first choice in the face of a larger-than-life human being? Flee.
It takes a lot of stress for a tarantula to try to bite a person, but it will happen under certain circumstances. If you find yourself in this unfortunate position, you can find some peace of mind knowing that tarantula venom is not deadly to humans. At worst, it may come with a bit of itchiness and discomfort for a few days, Holmes said.
"There isn’t any record anywhere of someone dying from a tarantula bite," she said. "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."
Even so, remember, it's illegal to harass wildlife, so don't invade their space.
Holmes said about 30 years ago, you could go outside at night in September and October and 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."
Tarantulas face other challenges as well, Holmes explained. They are prey for tarantula hawk wasps, birds, coyotes, house cats, and other animals.
Want to learn more?
You can see tarantulas at the Butterfly Pavilion in Westminster, which is open 9 a.m. to 5 p.m. seven days a week with timed entry. Entry ends at 4:15 p.m.
We’d love to see your tarantula pictures and videos! Join the Our Colorado photography group at www.Facebook.com/groups/OurCO to share them.
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