Spider Season in Utah: Black Widows & Hobo Spiders

Q: Why are there so many spiders in my house in Utah right now?

Spiders start turning up indoors around August 15, the wandering peaks between September 1 and October 15, and it fades by November 15. Those are male house spiders and funnel weavers looking for mates, plus spring hatched spiders that have finally grown large enough to notice. The widow record in Utah peaks in the same stretch, because females are at full size.

Q: Are there joro spiders in Utah?

No verified joro spider record exists in Utah yet. The species has spread outward from north Georgia since 2014 and first records keep appearing in new states, so the year by year series on the national page is the thing to watch. A large yellow and black spider on a web here is almost always a yellow garden spider, which is native and of no medical concern.

Q: Are there black widows in Utah?

Yes. Utah has one widow species with verified records: the western black widow (1,941 records). Widows build low tangle webs in undisturbed corners: woodpiles, meter boxes, sheds, block wall gaps and the undersides of outdoor furniture. They are shy, stay on the web, and bite when pressed against skin, which is why gloves for the woodpile and a shake of stored shoes remove most of the risk.

Q: Are there brown recluse spiders in Utah?

No recluse species reaches the record threshold in Utah. The brown spider in a Utah house is a funnel weaver, a cellar spider, a woodlouse spider or a house spider, and the violin mark people look for appears on several of them.

Q: Where do widows and recluses live in Utah?

Wasatch Front garages, block walls, window wells and irrigation boxes. Red rock country outbuildings and slickrock cracks. Basements and window wells across Salt Lake and Utah counties. The verified record clusters where people live and look, so Salt Lake and the Wasatch Front carries the most records and roadless country the fewest.

The list

The one widow or recluse species recorded in Utah

Every species below has verified, photograph backed records in Utah. The counts come from iNaturalist and measure how often people find and photograph each spider, never how many there are: a species of packrat nests will always look rarer than one of garages.

Species	Group	Verified records	What to look for
Western black widow Latrodectus hesperus	Widow	1,941	The black widow of the western states. Glossy black with a red hourglass below, webbing in garages, block wall gaps, irrigation boxes and the undersides of patio furniture.

Often asked about in Utah.

Hobo spider (Eratigena agrestis, 409 records): A brown funnel weaver of the Pacific Northwest and northern Rockies, found in basements, window wells and ground level clutter in late summer. Often asked about, and often confused with the giant house spider that shares its range.
Northern yellow sac spider (Cheiracanthium mildei, 101 records): A small pale yellow green spider that walks ceilings and window frames at night and rests in a silk sac in a corner by day. The spider most often met indoors across the Northeast and upper Midwest.

A glossy black widow spider hanging upside down in her web on coarse cloth, the red hourglass on the underside of the round abdomen in full view — A black widow from below: the red hourglass on a glossy round abdomen, hanging upside down in a low tangle web. The northern black widow's hourglass is usually split in two. “Adult Female Black Widow” by Shenrich91, CC BY-SA 3.0

A barn funnel weaver on a white ceiling seen from above, brown with two dark stripes on the front body segment and a mottled abdomen, its legs spread wide — For contrast, the barn funnel weaver that makes up most of the autumn indoor record: striped front segment, mottled abdomen, a sheet web with a funnel. Of no medical concern. “Tegenaria-domestica-chb” by Chb, CC BY 3.0

Interactive

Where each species has been found in Utah

Pick a species. The coloured cells are places where somebody photographed one and the identification was confirmed, redrawn as records are added. It thins over roadless country and thickens around towns, because that is where people look.

Coloured cells are verified Latrodectus hesperus records on iNaturalist, brighter where more have been logged. This is where people have found and photographed the species, so it thins out over roadless country and thickens around parks and towns. It is a record map, not a drawn range boundary. See the underlying records.

The season

When spiders come indoors in Utah

Indoor sightings in Utah pick up around August 15, peak between September 1 and October 15, and fade by November 15. The wanderers are mature male house spiders and funnel weavers searching for females, plus spring hatched spiders that have finally grown large enough to see. The widow spiders follow the same calendar because females are at full size; the busiest month in the Utah record is September.

Widow spider records in Utah, by month

1,942 research grade records of widow spiders in Utah, grouped by the month observed.From the iNaturalist snapshot taken 2026-09-19.

What the chart counts. Records, and a record needs a spider and a person with a camera. Spring spikes in some states are a late April bioblitz. Switch to the effort adjusted view and each month is divided by every research grade observation logged in Utah that month, which strips most of that out. Neither view is a population count.

A large dark funnel weaver spider standing in the white basin of a bathtub, long legs spread on the enamel — A funnel weaver in a bathtub, the classic September find. Smooth enamel is the one surface a wandering male cannot climb back out of, which is why the tub and the sink collect them. “Spinne-Tegenaria-domestica 01” by Traumrune, CC BY-SA 3.0

Identification

The spiders people photograph as widows

Most spiders reported as a widow or a recluse in Utah are one of the species below. The tells are visible from a comfortable distance, and a spider left alone in its corner stays there.

A widow is glossy, round bodied, and hangs upside down in a low tangle web with a red or orange hourglass underneath. A recluse is plain tan with six eyes in three pairs, a darker violin on the front segment, and legs with no bands and no spines. A violin shaped mark on its own is not a recluse: many harmless brown spiders carry one, and it is faint on many real recluses. A bite is never an identification. Skin reactions have dozens of causes, and Poison Control on 1-800-222-1222 will ask about symptoms, never for a species name.

Mistaken for a black widow

False widow

Steatoda grossa

Purplish brown rather than glossy black, with pale markings on top of the abdomen and nothing underneath. The same tangle web in the same corners, which is why it is photographed as a widow more than any other spider.

Triangulate cobweb spider

Steatoda triangulosa

Small, brown, with a row of pale triangles down the abdomen. Lives in the same low corners and window frames a widow would, and turns up indoors far more often.

Common house spider

Parasteatoda tepidariorum

Mottled tan and brown with a rounded abdomen, in messy cobwebs in ceiling corners, under eaves and behind furniture. The most photographed spider in American houses, and an autumn indoor regular.

If someone is bitten

What to do about a spider bite in Utah

First

Wash the bite with soap and water. That is the whole of the first aid. Skip creams, heat, ice and anything from a kitchen cupboard.

Then

Call Poison Control on 1-800-222-1222. Free, staffed around the clock, and they will tell you what to watch for over the next hours. They ask about symptoms, never for a species name.

Go to a hospital

For muscle cramping, sweating, spreading pain, or a wound that keeps getting worse over a day or two. Those are the signs that matter after a widow or recluse bite, and treatment depends on them, never on identifying the spider.

About the spider

A bite is never an identification. Skin reactions have dozens of causes and most marks blamed on spiders are something else. If the spider is already dead and in a container, bring it; never hunt for one.

Poison Control: 1-800-222-1222, any time, any state.

Common questions

Utah spider season FAQ

Why are there so many spiders in my house in Utah right now?

Are there joro spiders in Utah?

Are there black widows in Utah?

Are there brown recluse spiders in Utah?

Where do widows and recluses live in Utah?

How do I tell a widow or recluse from a harmless spider?

A widow is glossy, round bodied, and hangs upside down in a low tangle web with a red or orange hourglass underneath. A recluse is plain tan with six eyes in three pairs, a darker violin on the front segment, and legs with no bands and no spines. A violin shaped mark on its own is not a recluse: many harmless brown spiders carry one, and it is faint on many real recluses. A bite is never an identification. Skin reactions have dozens of causes, and Poison Control on 1-800-222-1222 will ask about symptoms, never for a species name.

What should I do if I am bitten by a spider?

Wash the bite with soap and water and call Poison Control on 1-800-222-1222, which is free and staffed around the clock. Go to a hospital for muscle cramping, sweating, spreading pain, or a wound that keeps getting worse over a day or two, which are the signs that matter after a widow or recluse bite. Treatment depends on the symptoms and never on naming the spider, and most marks blamed on spiders have another cause.

Also indoors this season

The rest of your Utah autumn

Utah venomous snakesThe other animal people fear on sight, with the same answer: a short real list and a long list of lookalikes.Utah fall invadersStink bugs, boxelder bugs and lady beetles head for the siding in the same weeks the spiders wander.Utah rodent seasonMice move toward buildings as the nights cool, and the gaps they use are the gaps spiders use.

More Rockies spider season pages

Species lists, record counts and monthly curves are research grade observations from the iNaturalist API, aggregate counts only, snapshot 2026-09-19 with the curves read live in your browser. They measure how often people find and photograph a species, never how many there are, and a species with no record here may still live here. Season windows are drawn from those curves and are climatological typicals. See every record behind this page. For any bite, wash with soap and water and call Poison Control on 1-800-222-1222. National picture: spider season by state.
Hero image: “Adult Female Black Widow” by Shenrich91, CC BY-SA 3.0

Spider Season in Utah: What Lives Here and When It Comes Indoors

Spiders in Utah, by the numbers