ST. GEORGE — As the days grow colder, Southern Utah’s tarantulas are completing their annual moonlit quests for romance. And soon, sightings will be scarce again until next year.
While they spend most of their time underground, each year on the cusp of summer and fall, male tarantulas begin wandering the desert — sometimes traveling many miles — in search of a mate, said Amanda Barth, native insect conservation program leader for Utah State University.
“Depending on how abundant their food sources are, the migrations can be pretty large,” she said. “This is when we start seeing them because ordinarily, they’re quite reclusive.”
“It’s like a local phenomenon,” Barth continued. “I think it’s a special thing for people to get an opportunity to see. Not to have it be scary but to have it be special. … Be inspired by them — check them out. Take an opportunity to watch them for a second with a flashlight and be excited about this special thing that chose your path.”
The males have undergone their final reproductive molts, shedding their old skin as they reach sexual maturity. They’re several years old before making what is often their final journey.
Tarantulas are cold-blooded, and how long the migration lasts is often temperature-dependent. Barth said that the arachnids require warmer days to be active and maintain their stamina. Other factors could include day length and the amount of moisture.
As the migration ends, surviving male tarantulas retreat underground in late October or early November, but most won’t survive the winter. Barth said they hunt less while migrating, usually consuming high-calorie meals beforehand, and are mostly “spent” by their journey’s end.
Female tarantulas have much longer life spans, with some species surviving for decades. After mating, they sometimes eat the males as they prepare to lay hundreds of eggs.
Finding a meal
While tarantulas’ meals typically consist of crickets and other nocturnal invertebrates, they’ve also been known to eat small mice, birds, lizards, snakes and other similarly-sized animals.
They hunker down in their burrows, lining the entrance with webbing, on which they place their “very sensitive, little feet” to detect vibrations, Barth said.
“It’s giving them the ability to measure the distance and direction of that prey,” she said. “So they don’t have to see it to know exactly where it is, and then they pounce on it. So they’re ambush predators, which saves them energy.”
Observing tarantulas in the wild
Tarantulas are nocturnal and most often observed at night or sunset. They typically avoid noise and fast movement as they have poor eyesight, Barth said, adding that they have “old school eyes and very simple lenses.” But they’re good at detecting vibrations using the hairs on their bodies and can see movement, contrast and light.
Locals are most likely to see tarantulas in the genus Aphonopelma. Local species include the desert tarantula — Aphonopelma iodius — and Grand Canyon black tarantula — Aphonopelma marxi.
Southern Utah is in the northernmost part of the spiders’ native range, according to Wild Aware Utah. Still, they can be found as far north as Cache County and are commonly seen in Washington and Iron counties.
Female tarantulas have larger abdomens, while males “don’t have as much junk in the truck,” Barth said.
One of their greatest defenses is hiding and “just being wary is partly their strategy to stay alive,” Barth said.
While tarantulas are venomous, they’re not dangerous to humans unless they’re allergic and unlikely to bite unless handled.
“The last thing on (a migrating male’s) mind is attacking somebody,” Barth said. “It’s like, ‘Leave me alone, please. I’m on my way, trying to do my thing.'”
However, they sometimes defensively fling small hairs from their underbodies, called urticating hairs, which can irritate skin and eyes or cause an allergic reaction.
While typically docile, people shouldn’t take them home, as they’re unlikely to survive.
“And you’ll have just killed it, and you’ll feel bad about that,” Barth said. “So don’t do it. … This is not the time to get a free tarantula.”
‘Poster child for the desert’
To support the species, Southern Utahns can reduce the light in their yards, as tarantulas prefer to move under cover of darkness, and light pollution is a common issue for other local creatures.
Additionally, residents can limit their use of pesticides, insecticides and rodenticides.
“(It’s) going to impact the health of tarantulas because that directly impacts their food source, or they end up eating something that has been exposed to some toxins,” Barth said. “They are your beneficial pest managers … And having more tarantulas means that you’re keeping those problematic animals at bay.”
These “micro-predators” are indicators of environmental health, Barth said, explaining that observing tarantulas on the landscape suggests there are resources available to support them.
“So that means there’s enough insects and small animals for them to eat and that the insects and small animals have enough food to eat,” she said. “So it’s kind of a pyramid.”
“For me, as an ecologist, that’s a really important factor to pay attention to because I’m always looking for ways to assess how healthy the environment is,” Barth continued. “And we don’t know what would happen if we lost tarantulas.”
Tarantulas are a food source for lizards, snakes, birds, coyotes, foxes and tarantula hawks, among other species. And should the spiders disappear, the ecosystem could be imbalanced, Barth said.
“They are just an interesting player in the desert, and they’re also kind of like a poster child for the desert,” she said. “Don’t forget that you live as a part of nature.”
LouAnn Schmidt-Wirick and Zion National Park contributed some clips for the video at the top of this article.
Photo Gallery
A tarantula navigates the fragile soils at White Dome Nature Preserve, St. George, Utah, Oct. 12, 2023 | Photo by Alysha Lundgren, St. George News A tarantula navigates the fragile soils at White Dome Nature Preserve, St. George, Utah, Oct. 12, 2023 | Photo by Alysha Lundgren, St. George News A tarantula navigates the fragile soils at White Dome Nature Preserve, St. George, Utah, Oct. 12, 2023 | Photo by Alysha Lundgren, St. George News A tarantula navigates the fragile soils at White Dome Nature Preserve, St. George, Utah, Oct. 12, 2023 | Photo by Alysha Lundgren, St. George News A tarantula navigates the fragile soils at White Dome Nature Preserve, St. George, Utah, Oct. 12, 2023 | Photo by Alysha Lundgren, St. George News A tarantula navigates the fragile soils at White Dome Nature Preserve, St. George, Utah, Oct. 12, 2023 | Photo by Alysha Lundgren, St. George News A tarantula navigates the fragile soils at White Dome Nature Preserve, St. George, Utah, Oct. 12, 2023 | Photo by Alysha Lundgren, St. George News A tarantula navigates the fragile soils at White Dome Nature Preserve, St. George, Utah, Oct. 12, 2023 | Photo by Alysha Lundgren, St. George News A tarantula navigates the fragile soils at White Dome Nature Preserve, St. George, Utah, Oct. 12, 2023 | Photo by Alysha Lundgren, St. George News A tarantula wanders the desert near a Mojave desert tortoise, date and location unspecified | Photo courtesy of Alan Holben, St. George News A tarantula wanders the nighttime desert in search of a mate, Washington County, Utah, August 2016 | Photo by Mori Kessler, St. George News A tarantula wanders the nighttime desert in search of a mate, Washington County, Utah, August 2016 | Photo by Mori Kessler, St. George News A tarantula hides in hay, date and location unspecified | Photo by Alysha Lundgren, St. George News A tarantula wanders the nighttime desert seeking a mate, date and location unspecified | Photo by Alysha Lundgren, St. George News A tarantula hides in hay, date and location unspecified | Photo by Alysha Lundgren, St. George News A tarantula navigates the fragile soils at White Dome Nature Preserve, St. George, Utah, Oct. 12, 2023 | Photo by Alysha Lundgren, St. George News
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