The tarantulas will be coming out of hiding soon in southeastern Colorado, but there’s nothing to fear (that would be arachnophobia) as they are pretty harmless. And you shouldn’t think of the annual phenomenon as a migration or invasion, as it’s sometimes described.
Mating season begins in late August and peaks in mid-September, according to Whitney Cranshaw, a recently retired Colorado State University entomologist. Males of the species that live in southeastern Colorado, known as Texas brown tarantulas or Oklahoma browns, emerge from their burrows when they reach adulthood at around 8 years old.
That’s when they go on what Cranshaw describes as a “walkabout” in search of females, who remain in the vicinity of their burrows. It’s a final fling for the guys, as it were, because those males are doomed to die later this season. Females live 20-25 years.
“The term ‘migration’ is misleading, as that indicates there is some directed movement from one location to another,” Cranshaw said. “And this was a huge source of confusion in media reports that broke out all over in 2019. I heard of people expecting to see some sort of invasion of migrating tarantulas from Oklahoma into Colorado, because the name Oklahoma brown was used.”
In fact, those media reports sent so many folks off in search for the supposed great tarantula invasion that they caused distracted driving on rural roads, creating safety concerns.
It’s understandable why some folks would be interested in seeing them, though. Tarantulas of this species (aphonopelma hentzi) are about four inches across, including legs. They may look scary, but you have nothing to fear if you see one.
“Tarantulas are not aggressive and they do not have venom that is dangerous to humans,” Cranshaw said. “Only once have I been bitten, and it was because I foolishly grabbed one by hand. It made a small slice in my finger, sort of like a mild paper cut.”
Tarantulas defend themselves not with bites but with the hairs on their bodies, Cranshaw said.
“If disturbed, they can flick some of these (hairs) using their legs, and the hairs are spined and can be irritating,” Cranshaw said. “Particularly if they got into the eye of a potential predator. I have experienced it once with a different species, which I was holding for hours while talking with school groups, and got some hairs between my fingers, which itched a lot for days.”
For years, Cranshaw collected tarantulas to provide students in a class he taught called “Insects, Science and Society.” About five years ago his wife, Sue Ballou, began joining him on his nocturnal spider hunting. “It’s my favorite date night, what can I say?” Ballou said.
“We work as a team, with her driving and spotting,” said Cranshaw, who retired last month after 37 years at CSU. “I hop out and scoop them up when we come across them. I will probably do it again this year, Sue wants to. However, with all the publicity and all the cars last year, it is not the same.”
Tarantula habitat is widespread, but they live in pockets in undisturbed prairies and rangeland, Cranshaw said. And while they roam the rangeland, people tend to see them when they are crossing roads that run through their habitat. Places where they might be observed include Highway 109, south of LaJunta in Otero County, and on roads leading into Vogel and Picketwire canyons. Another place, Cranshaw said, is Highway 350 between Trinidad and Timpas. Activity tends to pick up around dusk.
Some years are better for observing than others, and last year was a bad one. Cranshaw believes that was due to a severe drought eight years ago that caused the survival rate of young tarantulas to be low.
“A lot of people went to look for them last year and many did not see any,” Cranshaw said. “I did not see any.”
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