Holmes Lawn & Pest Blog

The Woodlouse Spider

Woodlouse Spider

In the United States, the woodlouse spider was once only found in certain coastal states. Populations of these spiders are becoming more common, especially in western states like Utah. As part of the Dysdera genus of hunting spiders, woodlouse spiders get their name from their main source of food–woodlice. This spider will also feast on other small invertebrates, such as silverfish, house centipedes, cockroaches, crickets, and others. Though it has a somewhat striking and unsettling appearance, the woodlouse spider is not one of the more dangerous spider species in Utah, but it can still do some harm to people if they are provoked. 

Woodlouse Spider Appearance

Woodlouse spiders grow up to 15 millimeters in length, but their physical attributes make them much more intimidating than their small stature would suggest. They are characterized by a cephalothorax that is typically bright red and segmented legs that range from that same bright red color to a lighter orange. This red color warns predators that this spider is aggressive and will fight back if attacked. Woodlouse spiders are one of the few species of spiders to have only 6 eyes instead of 8, and those eyes are arranged in a small semicircle at the front of the cephalothorax. 


Just below the eyes are this spider’s most prominent and feared feature–its fangs. The chelicerae, or mouthparts, of this spider include fangs that are disproportionately large compared to the rest of its body. These fangs are incredibly strong and are capable of breaking through the tough exoskeleton of the spider’s common prey, which includes beetles, cockroaches, pillbugs, and other creatures with hard exteriors. 


The abdominal area of the woodlouse spider is roughly the same size as the cephalothorax, and it is typically a tan to light brown color. The color of the abdomen and the overall size of the woodlouse spider make it a common “false recluse” species. Many people see the sandy-colored abdomen and believe they are seeing a desert recluse or brown recluse, which are much more dangerous to humans than the woodlouse spider. An easy way to differentiate a woodlouse spider from a recluse spider is by the large fangs of the woodlouse spider. If you are unsure and believe you may be dealing with a recluse, it is always best to stay away from the spider and seek professional help.

Life Cycle And Habits

Woodlouse spiders are known to be aggressive towards predators, prey, and even their own kind. It is believed that these spiders mate primarily in spring, and the occasion is alway a contentious affair. Woodlouse spiders are especially aggressive towards one another while mating, and it is not uncommon for the act to result in death. Their large and dangerous fangs are often used to attack one another during or after the mating process. 


The female lays her eggs shortly after mating occurs. Eggs are laid in a silken sac made by the mother, which typically contains up to 70 eggs that are looked after by the mother. Once hatched, woodlouse spiderlings stay close to their mother and rely on her for protection in the early stages of their lives. The mother makes a silk, oval-shaped enclosure to protect herself and her spiderlings from predators. The woodlouse spider mother is known to fiercely defend her offspring while they are with her in this enclosure. 


After a period that is believed to be up to a few weeks, the spiderlings go out on their own and search for food and adequate shelter. These spiders reach full maturity around 18 months, and they typically live an additional 2 two 3 years as adults. When looking for suitable places to call home, woodlouse spiders prefer dark, quiet crevices or areas hidden under rocks and debris. The spider’s name comes from its diet that consists largely of small invertebrates, such as woodlice, and small cracks in decaying wood make the perfect home for woodlouse spiders. 


While woodlouse spiders do not spin webs, the silk enclosures they make do serve as a type of “house” that provides protection from predators and the elements. During the day, these spiders are often resting and waiting for nightfall inside of their silken houses. Woodlouse spiders are nocturnal hunters that actively seek their prey at night rather than waiting for their victims to get caught in a web. It is not common to see woodlouse spiders active during the day.

Are They Dangerous?

Though the woodlouse spider is aggressive towards its prey and has the appearance of a tiny monster, they are not known to be harmful or even aggressive towards humans. They can inject venom into their victims, but the venom of these spiders is not significantly harmful to humans. Still, the bite of a woodlouse spider will cause mild discomfort, as the large fangs they use to kill prey are the same fangs that would be used to bite a human if it were to feel threatened. Fortunately, the woodlouse spider prefers to make a home in nature and will most likely run and hide from a human presence. If you do encounter this spider, leave it alone, and it will likely leave you alone. If one does find its way into your home or near you, do not attempt to handle it. Its bite is not lethal, but it will leave an irritating welt that could potentially become infected. 


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