Utah is home to tarantulas, which are large, hairy spiders belonging to the family Theraphosidae. These spiders are primarily restricted to specific geographic areas, mainly in the southern and arid regions of the state. Tarantulas spend most of their lives hidden underground in burrows. Their presence is a natural part of Utah’s arid ecosystem.
The Utah Tarantula Species and Habitat
Utah’s tarantulas belong to the genus Aphonopelma, including species adapted to the American Southwest. The most commonly encountered species is Aphonopelma iodius, sometimes called the Great Basin blonde tarantula. Other species, such as Aphonopelma marxi and Aphonopelma prenticei, are found primarily in the southern and southeastern regions. These spiders are strongly drawn to dry habitats, including the Mojave Desert transition zones and arid scrublands found largely in Southern Utah.
Tarantulas construct deep, silk-lined burrows in the dry, soft soil. These burrows are crucial for survival, offering protection from extreme temperatures. They often obstruct the entrance with a plug of silk and dirt to maintain consistent humidity and temperature inside. Females can live for decades, spending nearly their entire lives within this structure.
They are ambush predators that wait just inside the entrance. They use ground vibrations to detect passing prey, such as insects, smaller spiders, and small rodents, before darting out to capture them.
Tarantula Behavior and Safety
Utah’s tarantulas are not aggressive and rarely seek out confrontations with humans or pets. They are nocturnal and spend most of their time in subterranean burrows, which is why sightings are infrequent. They are generally considered harmless to humans, and their primary defense mechanism does not involve biting.
When threatened, the tarantula uses its abdomen to kick off a cloud of tiny, barbed urticating hairs. These hairs cause irritation, itching, and rash upon contact with skin or eyes, serving as a deterrent to predators. A bite is a last resort, and while venom is present, it is not considered medically significant to people.
A tarantula bite is typically compared to a mild bee sting, causing localized pain and slight swelling. Since the spiders are slow-moving and prefer to retreat, bites almost exclusively result from accidentally stepping on or deliberately provoking the animal. If an encounter occurs, the best course of action is to leave the spider alone.
The Annual Tarantula Migration
The most visible event involving Utah’s tarantulas is the annual male migration, which occurs during the late summer and early fall. This seasonal movement typically begins around late August and can continue through October. The movement is a mass exodus of mature males leaving their burrows for the single purpose of finding a mate.
The females remain in their burrows, so the spiders observed wandering across the landscape are almost exclusively males. These males, having reached sexual maturity after approximately ten years, walk considerable distances searching for a female’s burrow. This behavior often brings them into view, especially as they cross roads and open areas in the southern counties.
The males have a shorter lifespan than the females. This is partly because they spend the rest of their lives above ground, exposed to predators and the elements.