What’s the Deal with Colorado’s Tarantulas?

Every September, the same story hits the news: “The tarantulas are migrating again!” You’ll see it on social media, hear it on the radio, and occasionally catch a podcast chatting about it. It feels like every year, Colorado catches what I like to call “tarantula fever.” But despite the hype that draws adoring fans from around the world, the news usually gets one big detail wrong: the tarantula “migration” isn’t a migration at all. It’s the ultimate season of Love Is Blind, with a tragic twist at the end.

For those who are new here, hi! My name is Carly, and I’m a professional wildlife guide with Reefs to Rockies, based in Denver, Colorado. I was a field biologist for eight years before moving into wildlife guiding, and I studied entomology for my master’s degree. While I’m not a “leading expert” on tarantulas, I do know my way around the world of creepy crawlies. Every year I lead a group to see these tarantulas in action.  

So, what’s the deal with Colorado’s tarantulas? The most common species we get here is the Oklahoma brown tarantula. (We have one more on the Western Slope, the Grand Canyon black tarantula, but we’re not talking about that one today.) Starting in mid-August, male Oklahoma browns leave their burrows for good to answer the call of love. It takes five to seven years for a male to reach this point in his life. The wandering peaks in mid-September, which is when you’re most likely to bump into one crossing a road. Night after night, they roam the plains of southeastern Colorado, hoping to stumble onto a female’s burrow. If a male is lucky enough to find one, he gently taps on the silk she has laid out around the entrance. If she’s receptive, she’ll come out, and he’ll use his pedipalps to transfer his sperm into a storage pocket in the female’s abdomen, called the spermatheca. I know, the stuff of romance novels. The female then returns to her burrow and keeps his sperm stored until next summer, when she’ll use it to fertilize her eggs. After that romantic encounter, our guy wanders off again in hopes of finding another lover.

So where does migration come into this? It doesn’t. Migration is the annual movement of entire populations of animals to take advantage of seasonally abundant resources in different parts of the world. Take birds, for example. Every spring, many of the sandhill cranes that winter in New Mexico fly as far as Alaska and even Siberia to cash in on the insect boom of the northern summer. That’s migration.

As you read above, Oklahoma brown tarantulas aren’t moving en masse from point A to point B. It’s only the mature males wandering around looking for females. Every female stays in her burrow for her entire life, which has been documented at up to 30 years in captivity. Tarantulas aren’t migrating, but they are wandering. Here in Colorado, those in the know call it the “tarantula walkabout.”