Brown tarantulas are on the move as the arachnids embark on a mating journey – The Arizona Republic

Across the Southwest, thousands of male brown tarantulas are marching across the landscape, their journey part of an annual migration of sorts, when the hairy creatures leave their burrows in search of a mate. 

While the event is often called a migration, the spiders don’t migrate in the way that most animals do, from one specific spot to another. Rather, the saucer-sized arachnids leave their home burrows specifically to mate, which can take them anywhere from several hundred feet to several miles in any direction. 

“They move really far. I think I had one of mine move almost a kilometer while I was monitoring him,” said Margaret Janowski-Bell, a biology professor at Victoria College in Victoria, Texas, who studied the movement of males for her graduate work. “The males that I looked at moved in all different directions. What I saw were males looking for females across the landscape.”

Scientists believe the spider’s trek is spurred by many factors, including age, pheromones, and the change in seasons, which means the exact timing of their journey depends on where they are.

When males reach sexual maturity, usually at about 10 years, their first order of business is procreation, leading to a mass dispersal, said Evan Waite, a Ph.D. student in entomology at Arizona State University. “All the males that have matured in the past year, they’re going to be the ones out making this journey.” 

The life span of the male tarantula, also known as the Oklahoma or Texas brown tarantula, can be up to 12 years. That’s brief when compared to their female counterparts, which can live up to 30 years. But the eager males make good use of their time, siring up to 1,000 eggs per female.

In Arizona, males have been observed starting their search during the monsoon, according to the University of Arizona’s Yavapai County Cooperative Extension program. One master gardener in Prescott had observed the fuzzy creatures crawling on her rural farm.

The females are misunderstood

Despite the common assertion that females routinely kill males, this isn’t always the case. During the short season, males can make the sojourn to several females’ burrows, according to Janowski-Bell. 

“(I)t’s a misnomer that the females will kill the males,” Janowski-Bell said. “In a normal year, they will go from female to female. They’ll cohabitate.”

After mating, the future for males doesn’t look bright. Either they die of starvation, cold weather, or in some cases, they are eaten by females who mistake them for prey. As for the females, Waite said they have a gestation period of up to several months and drop their eggs in the spring. 

“The female generally will kind of hunker down for the winter, and she won’t drop or lay her egg sac until March-ish of the following year,” Waite said. 

After that, the eggs can take several months to hatch, said Cristi Painter, a U.S. Forest Service wildlife biologist who studies the tarantulas in the Comanche and Cimarron National Grasslands in Kansas. 

The species range from western Texas all the way to Arizona, but the epicenter of their annual mating journey appears to be southeastern Colorado, near La Junta, where Painter works. There, dozens of spiders have been seen within an hour and a half time frame, crawling along roadsides and through patches of desert.

In other places, including Arizona, the species appears to be mostly solitary. 

They prefer arid, dry climates, where burrows can easily be excavated, said Shaku Nair, an entomologist and associate in the University of Arizona Extension’s Community Integrated Pest Management.

“Their ideal habitat would be grasslands, or any kind of natural area, at least in Arizona,” Nair said. “I would say natural areas with grass or short vegetation, sparse vegetation.” 

Tarantulas face natural risks

One telltale sign that they are out and about, Painter said, is the presence of tarantula hawks, a predatory wasp that relies exclusively on brown tarantulas for breeding. 

“They will pollinate during the day, but then at night, they’ll go sting a tarantula, and it paralyzes it,” Painter said. “They paralyze it, pull it off, plunk it in a hole, lay its eggs on it, and then the larvae eat their way out.”

Among other dangers, Painter added, are predators such as coyotes, fire, weather, and roads. 

At lengths of up to 6 inches, the spiders tend to be pretty conspicuous. They can be identified by their large brown bodies and orange-tinted hairs on their abdomens. When threatened, they will flick the hairs on their backs at suspected danger. 

“They do have some defense mechanisms that they can use,” Waite said. “And their first line of defense that they will always try to go to first is this structure that they have on their back called urticating hairs. If they get flicked into your nose, or your skin, or anything like that, it feels like a little splinter. And it’s really itchy and irritating.”

If you see one, fear not. They don’t pose any real danger to humans. They can and do bite, but a bite wouldn’t be fatal unless there’s an allergic reaction. In most cases, the spiders will give a clear warning signal by raising their front legs and bearing their large fangs. 

In some places, onlookers are encouraged to get up close and personal with the traveling spiders. It’s advised that viewers look and don’t touch. They are fragile, and most experts say that the slightest fall can injure the fury crawlers. 

“I would not recommend touching them, I would not recommend getting in their way at all actually, just observe them from a distance,” Nair said. “If you’re lucky enough to see some, just don’t interfere with them. I would say just leave them alone and just observe them from a distance and marvel at their journey.”

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Lindsey Botts is an environmental reporter for The Arizona Republic/azcentral. Follow his reporting on Twitter at @lkbotts and Lkbotts on Instagram. Tell him about stories at lindsey.botts@azcentral.com.

Environmental coverage on azcentral.com and in The Arizona Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust. Follow The Republic environmental reporting team at environment.azcentral.com and @azcenvironment on Facebook, Twitter and Instagram.