Hobo Spider, Tegenaria agrestis

Habits and Traits of Hobo Spiders

Hobo spider.
Hobo spiders can not be identified accurately by the naked eye. Whitney Cranshaw, Colorado State University, Bugwood.org

The hobo spider, Tegenaria agrestis, is native to Europe, where it is considered harmless. But in North America, where it was introduced, people seem to believe the hobo spider is among the most dangerous creatures we can encounter in our homes. It's time to set the record straight about the hobo spider.

Description:

The features that distinguish Tegenaria agrestis from other similar-looking spiders are only visible under magnification.

Arachnologists identify hobo spiders by examining their genitalia (reproductive organs), chelicerae (mouthparts), setae (body hairs), and eyes with a microscope. Directly stated, you cannot accurately identify a hobo spider by its color, markings, shape, or size, nor can you identify Tegenaria agrestis with the naked eye alone.

The hobo spider is generally brown or rust in color, with a chevron or herringbone pattern on the dorsal side of the abdomen. This is not considered a diagnostic trait, however, and cannot be used to identify the species. Hobo spiders are medium in size (up to 15 mm in body length, not including the legs), with females slightly larger than males.

Hobo spiders are venomous, but not considered dangerous in their native European range. In North America, hobo spiders have been considered a species of medical concern for the past several decades, although there doesn't seem to be any scientific evidence to support such an assertion about Tegenaria agrestis.

No studies have proven that hobo spider venom causes necrosis of the skin in humans, as is often claimed. In fact, there has only been one documented case of a person developing skin necrosis after a hobo spider bite, and that patient had other medical issues also known to cause necrosis. Additionally, spider bites are extremely rare, and hobo spiders are no more inclined to bite a human than any other spider you might encounter.

Think You Found a Hobo Spider? 

If you are concerned that you may have found a hobo spider in your home, there are a few things you can observe to be sure your mystery spider is not a hobo spider. First, hobo spiders never have dark bands on their legs. Second, hobo spiders don't have two dark stripes on the cephalothorax. And third, if your spider has a shiny orange cephalothorax and smooth, shiny legs, it is not a hobo spider.

Classification:

Kingdom - Animalia
Phylum - Arthropoda
Class – Arachnida
Order – Araneae
Family – Agelenidae
Genus – Tegenaria
Species - agrestis

Diet:

Hobo spiders hunt other arthropods, primarily insects but sometimes other spiders.

Life Cycle:

The hobo spider life cycle is believed to live as long as three years in inland areas of North America, but just one year in coastal areas. Adult hobo spiders usually die in the fall after reproducing, but some adult females will overwinter.

Hobo spiders reach adulthood and sexual maturity in the summer. Males wander in search of mates. When he finds a female in her web, the male hobo spider will approach her with caution so he's not mistaken as prey. He "knocks" at the funnel entrance by tapping a pattern on her web, and retreats and advances several times until she seems receptive.

To finish his courtship of her, the male will add silk to her web.

In early fall, mated females produce up to four egg sacs of up to 100 eggs each. The mother hobo spider attaches each egg sac to the underside of an object or surface. The spiderlings emerge the following spring.

Special Behaviors and Defenses:

Hobo spiders belong to the family Agelenidae, known as the funnel-web spiders or funnel weavers. They construct horizontal webs with a funnel-shaped retreat, usually to one side, but sometimes in the center of the web. Hobo spiders tend to stay on or near the ground, and wait for prey from within the safety of their silk retreats.

Habitat:

Hobo spiders typically inhabit wood piles, landscape beds, and similar areas where they can construct their webs. When found near structures, they're often seen in basement window wells or other darker, protected areas near the foundation.

Hobo spiders don't usually live indoors, but occasionally make their way into people's home. Look for them in the darkest corners of the basement, or along the perimeter of the basement floor.

Range:

The hobo spider is native to Europe. In North America, Tenegaria agrestis is well-established in the Pacific Northwest, as well as parts of Utah, Colorado, Montana, Wyoming, and British Columbia (see Tenegaria agrestis range map).

Other Common Names:

Some people call this species the aggressive house spider, but there is no truth to this characterization. Hobo spiders are quite docile, and only bite if provoked or cornered. It's believed that someone christened the spider with this misnomer, thinking the scientific name agrestis meant aggressive, and the name stuck. In fact, the name agrestis comes from the Latin for rural.

It's also worth noting that an August 2013 analysis of European funnel-web spiders reclassified the hobo spider as Eratigena agrestis. But because this is not yet widely used, I've chosen to use the previous scientific name Tenegaria agrestis for the time being.

Sources:

  • Medical and Veterinary Entomology, edited by Gary R. Mullen, Lance A. Durden, 2009.
  • The Encyclopedia of Medical and Veterinary Entomology, by Richard C. Russell, Domenico Otranto, Richard L. Wa, 2013.
  • Family Agelenidae - Funnel Weavers, Bugguide.net. Accessed online December 3, 2014.