Biology of the Hobo Spider (Eratigena agrestis)

1. Classification & Appearance

Feature Description

Family Agelenidae (Funnel Weavers)

Size Medium-sized. Females are typically 9.5–16.5 mm body length; males 7–13.5 mm. Their leg span is generally smaller than the Giant House Spider.

Colour Brownish overall. The body is covered in fine hairs (plumose setae).

Markings (Difficult to Identify) Abdomen: Has a distinctive pattern of yellowish-brown V-shaped markings (chevrons) pointing toward the head. This pattern can be very indistinct. Sternum (underside): Generally has a light stripe running down the middle and lacks the pale spots on the sides that are often present on the Giant House Spider. Legs: Long, slender, and unbanded.

Identification Note It is extremely difficult to distinguish a Hobo Spider from its relatives (E. atrica and T. domestica) without microscopic examination of the reproductive structures by an arachnologist. Relying on markings, size, or colour is unreliable.

2. Habitat and Web

• Origin & Name: Native to European fields (agrestis means "of the field"). The common name "Hobo" came from the theory that it spread across North America along railway lines.

• Preferred Habitat: Outdoors in sheltered areas: under rocks, woodpiles, foundation perimeters, in tall grass, or in cracks in the ground.

• Web Structure: Builds a horizontal, non-sticky sheet web that funnels down into a tube-shaped retreat in a dark crevice. The spider waits in the funnel for prey to land on the sheet.

• Indoors: Hobo spiders often avoid human dwellings where they compete with the larger Giant House Spider (E. atrica). However, they are frequently found indoors in basements, crawl spaces, and garages, especially in the late summer and fall (August to October) when mature males wander widely searching for females.

3. Life Cycle

• Lifespan: Suspected to take about two years to mature into an adult.

• Reproduction: Males mate in late summer/fall and typically die shortly after. Females lay 1 to 4 egg sacs in the fall, which are deposited in a protected area (like under wood or inside the funnel retreat) and hatch the following spring.

4. Toxicity and Medical Status (Crucial Information)

The medical significance of the Hobo Spider has been heavily debated and, in North America, has been widely exaggerated and misrepresented in the past.

• Old Claims: Starting in the 1980s, the Hobo Spider was erroneously linked to cases of necrotic (flesh-eating) wounds in the Pacific Northwest, a condition properly caused by the Brown Recluse (Loxosceles reclusa), which does not live in Alberta.

• Current Scientific Consensus:

  • Venom is NOT Necrotic: Studies and expert reviews have concluded there is no clear scientific evidence that the Hobo Spider's venom causes necrotic skin lesions in humans.

  • CDC Status: The U.S. Centers for Disease Control and Prevention (CDC) no longer lists the Hobo Spider among spiders of medical concern.

  • Bite Effects: Bites are rare and defensive. When they do occur, symptoms are usually mild and temporary, involving only local pain, redness, and slight swelling—similar to a bee sting.

  • Misdiagnosis: Skin lesions commonly blamed on spider bites are far more often caused by Methicillin-resistant Staphylococcus aureus (MRSA) bacterial infections or other non-spider-related conditions.

In the context of Alberta, the Hobo Spider is not considered a dangerous species. The only spider in the province with medically significant venom is the Western Black Widow (Latrodectus hesperus).