Hobo spider or black widow? Telling Utah house spiders apart

The two spiders people worry about

Almost every spider call in the Salt Lake Valley comes down to two questions: is this a black widow, and is this a hobo spider? They look nothing alike, and they matter in very different ways.

Black widows are the spider of medical concern in Utah. Hobo spiders have a scary reputation, but the evidence doesn't back it up. Knowing which one you've found changes what you should do next.

How to spot a black widow

Adult female black widows are glossy black with a round abdomen and a red or orange hourglass on the underside. Males and young spiders are smaller, paler and often patterned, and they rarely cause problems.

The web is the best clue. Widows build messy, tangled, irregular webs low to the ground in sheltered spots, not neat orb webs.

• Window wells, especially with leaves or debris
• Wood piles, meter boxes and irrigation boxes
• Garage corners and under storage shelves
• Under decks, playsets and outdoor furniture

How to spot a hobo spider

Hobo spiders are brown, fast-running spiders with long legs that build funnel-shaped webs at ground level. The problem is that several harmless brown spiders look almost the same, including giant house spiders and other funnel weavers.

Telling them apart with confidence usually takes a close look under magnification. If you see a large brown spider racing across the basement floor in September, odds are it's a male hobo spider or a close look-alike out looking for a mate.

USU Extension says hobo spiders are found most often in Utah homes from August through October, when males wander looking for mates, and the species is now spread throughout northern Utah. The same source names the black widow as the major spider of medical concern in Utah and notes that the CDC does not list hobo spiders among spiders venomous to people. So the brown spider in your basement is usually a nuisance, while the black one in the window well deserves care.

Where they turn up in Salt Lake homes

Both spiders favor the lower, quieter parts of a house. Window wells are the classic spot, because they collect leaves, stay cool and trap the insects spiders eat. Basements, garages and storage rooms follow.

Keeping wells clear, sealing gaps under garage doors and cutting down the insects drawn to porch lights all reduce the number of spiders you see indoors.

What to do if you find one

Don't handle either spider with bare hands. If you want a positive ID, trap it under a jar, slide paper underneath and keep it for us.

• Wear gloves when reaching into window wells, wood piles and boxes
• Shake out shoes and gloves stored in the garage
• Seek medical care after a suspected black widow bite, especially with muscle pain or cramping
• Call for treatment if webs return within days of clearing them

Sources

• extension.usu.edu