Each year, male brown tarantula trek across Colorado to look for ladies.
From mid-September to mid-October, they leave the safety of their burrows to go on journeys that will take interesting turns as they face rejection, predators and fatigue.
Why they're on the move
Cara Shillington, a biology professor at Eastern Michigan University, doesn't consider the trek a migration because "this is not a one-way movement from one location to a different location."
Arachnid aficionados say although male tarantulas spend most of their lives in their underground burrows, they leave them to find female tarantulas once they reach sexual maturity.
"They get to this nice, reflective color on their exoskeleton. They'll look a lot prettier," said Chandler Peters, an entomology keeper at the Arizona-Sonora Desert Museum.
The females, who can live up to 30 years, never leave their burrows. And if the males snoop around too much under the earth, they could suddenly end up in another spider's burrow and become a meal, Shillington said.
By approaching a female's den from the outside, they are able to signal ahead of time to the females that they are lovers, not fighters, Peters said. They'll send vibrations and tap on the edge of her den. As she gets closer, he'll use hook-like structures on his front legs to restrain the female from immediately attacking him. As they wrestle, the male sticks a sperm package on her underside.
Male tarantulas are typically low on fuel during mating season, as they aren't eating or drinking at all, according to Dallas Haselhuhn, who studied Colorado brown tarantulas during his graduate program at Eastern Michigan University.
But after the deed is done, they have to muster what energy they can to move quickly to the next female. Because if a female spider is feeling particularly testy — or hungry — the male will become fast food.
"They're kind of risking a lot to do this, and this is a very dramatic, harrowing journey for them," Peters said.
The males may face other obstacles, such as predators and being hit by cars. And while climate change has notably been affecting other species, Colorado tarantulas may be more primed to handle it, Haselhuhn told NPR's Short Wave.
"I would expect that this group of tarantulas actually ends up being able to be that stronghold for the species, because they're used to such swings in temperature," he said.
Even if the males make it through mating season, they don't have much longer to live. They typically die naturally within a year of reaching their sexual peak, capping their life spans of eight to 15 years, Shillington said.
As for the females, they may hold onto their egg sacs a year or more, depending on factors such as their species or the population of their species in a given area. The amount of eggs that hatch depend on the female tarantula's size or how much food she has, but range from about 100 to 400, Shillington said.
Tarantulas are still a mystery
Tarantulas have become cultural mainstays in horror movies and as Halloween decorations. But there's still a lot to be discovered about them in real life.
Shillington said she still doesn't have answers on how far male tarantulas travel when they're mating, or what triggers them to leave. Is it their hormones? The humidity of monsoon season? The cold? Are they simply following the leader?
"It's just so amazing that everybody knows what tarantulas are," she said. "They're these big top predators within their environment, and yet, some basic questions, we still don't know."
Part of the puzzle is tarantulas are solitary and territorial animals. They stick to their burrows and don't interact much outside of mating.
Shillington said she has tagged several tarantulas and is collecting data to learn more about them. Haselhuhn has also put radio transmitters on tarantulas in his studies, but said, "We quickly found that it was pretty hard to track them down because they would be half-eaten inside the female's burrow."
Adding to the equation: There aren't enough people who research tarantulas and insects.
"People like mammals, they like furry things," Shillington said.
What else we know about tarantulas
Peters said though tarantulas face lots of threats, they do a pretty good job of defending themselves with the hairs on their body.
The hairs on their legs and the front of their bodies act as environmental sensors, which help them find prey, avoid predators and pick up vibrations in the earth and currents in the air, Peters said. They have urticating hairs on their abdomens and backs. They function similarly to a porcupine's quills, in that tarantulas will shoot them off to sting predators when threatened, Peters said.
Additionally, not all tarantulas live underground. The Colorado natives live there to insulate themselves from the cold, but tropic tarantulas prefer to tower in the trees, Shillington said.
They also come in lots of size and color variations.
They can be red, orange, brown, black, purple, green or blue, and "you get dwarf tarantulas up to the giant [Goliath] birdeaters, so whatever size you want, you can probably find," Shillington said.
Regardless, the fuzzy crawlers are generally harmless to humans. In fact, they help us, as they manage pests like cockroaches.
"If you have them in your area, give them their space and let them do their work, and they'll help make your life a lot easier," Peters said.
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