The Woodlouse Spider

In the United States, the woodlouse spider was once found only 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 it is provoked.

Woodlouse Spider Appearance

Woodlouse spiders grow between 10-30 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. The lighter, sandy color of the abdomen and the overall size of the woodlouse spider make it a common “false recluse” species.

Unique Characteristics

• Six eyes arranged in a semicircle
• Disproportionately large chelicerae and fangs
• Equally sized abdomen and cephalothorax
• Bright red-to-orange cephalothorax
• Sandy-colored abdomen
• Clearly segmented and bright-colored legs

Life Cycle

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 always 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 very soon after mating.

Eggs are laid and placed into a silken sac that can contain up to 70 at once.  ➥  Spiderlings stay close to their mother for protection.  ➥  The mother makes an oval-shaped enclosure for herself and her offspring to hide during the day.  ➥  Spiderlings venture off on their own after two to three weeks.  ➥  Woodlouse spiders reach full maturity around 18 months.   ➥  The average woodlouse spider lives up to three years.  

Habits

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. The creature’s chelicerae are incredibly strong for its size, and they are perfect for cutting through the exoskeletons of unlucky prey.

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 woodlouse spiders are aggressive towards prey and have the appearance of tiny monsters, 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 significantly harmful to people, but it will leave an irritating welt that could potentially become infected.

Call Holmes Lawn & Pest at (801) 616-5296 for more information on spiders and pest control in Utah.

We hope you enjoyed this blog post. Check out our last blog post on how to identify the most common Utah spiders and most recent blog post on the black widow spider.