Common House Spiders in Iowa: Identification & Bite Info

Common House Spiders Found in Iowa

Iowa is home to a variety of spider species that often find their way inside houses. While the majority of these house spiders are harmless to humans, some do have the potential to bite if provoked. Knowing how to identify the most common house spiders found in Iowa can help homeowners understand which ones they should watch out for.

Cellar Spiders

One of the most frequently encountered spiders hiding in Iowa homes is the cellar spider (Pholcus phalangioides). These long-legged spiders construct messy-looking webs in corners of rooms, behind furniture, or near ceilings. Their elongated bodies reach up to 9 mm in females and 7 mm in males. Cellar spiders have a light gray to brown color with faint markings on their abdomens.

Despite their spindly appearance, cellar spiders pose no danger to people. They do not defend territories and will flee from humans. Their small fangs cannot penetrate skin. These spiders mainly emerge at night to catch other household pests like flies, mosquitoes, clothes moths, and carpet beetles on their irregular webs.

American House Spiders

American house spiders (Parasteatoda tepidariorum) spin prominent cobwebs in sheltered locations outside homes. But they often wander indoors in search of insect prey and less extreme temperatures. This species reaches up to 15 mm body length and exhibits a round, pear-shaped abdomen patterned with variable mottled gray, brown, and black markings.

American house spiders share the same habitats with the black widow spider and brown recluse spider when living outdoors. But inside Iowa homes, this spider poses no safety risk to residents. They rarely bite humans unless held against bare skin. And their venom produces nothing more than temporary redness and mild pain around the bite site if it manages to pierce the skin.

Triangulate Cobweb Spiders

The triangulate cobweb spider (Steatoda triangulosa) is another spider inclined to building webs on vertical surfaces like siding, window frames, entryways, garages, basements, and sheds. During the day these brownish-gray spiders hide out of sight. At night they emerge to invert themselves in the center of their irregular cobwebs to lie in wait for prey.

In spite of their resemblance to black widow spiders, triangulate cobweb spiders lack toxic venom dangerous to humans. Still, they are one species that might bite defensively if threatened. The fangs do draw blood from skin in the process, but the venom only causes a mild burning sensation around the bite mark.

Grass Spiders

It is common to find grass spiders (Agelenopsis species) hiding within Iowa homes when weather extremes drive them to seek shelter. The funnel weavers construct flat, tube-shaped webs with a funnel retreat in grassy or wooded locations outdoors. But overnight they often invade garages, sheds, basements, and ground floor living spaces.

Funnel weaver grass spiders have brown or gray coloring with faint stripes or markings on their bulbous abdomens. Average size ranges from roughly one quarter inch to over an inch long depending on age and sex. These spiders flee from humans and rarely bite unless handled roughly or trapped against skin.

Jumping Spiders

Iowa houses frequently harbor jumping spiders that enter from gardens through cracks and crevices. These tiny terrestrial spiders crawl using six to eight eyes to hunt instead of webs. They pounce rapidly on their prey. Most species measure only 14 to 58 inch long and public black with variable white, red, or green markings.

Though jumping spiders appear intimidating due to their erratic movements, they pose minimal risk to people. They prefer fleeing to biting if approached by humans. And while their venom can pierce skin, it typically only causes temporary pain and inflammation around the bite site similar to a bee sting.

Wolf Spiders

Wolf spiders often invade Iowa homes during mating periods or while searching for overwintering shelter. They spend the warmer months hunting outdoors at night. These hairy spiders measure over an inch long with brown, black, white, and gray mottled markings as camouflage. Some lighter colored desert species also occur in the state.

All wolf spiders have toxic venom delivered through their large fangs. But most are reluctant to bite humans. They inject venom mainly to paralyze insect prey. Bites to people usually happen by accidental contact with skin or when trapped against the body. Resulting symptoms typically include swelling, redness, bruising, and pain around the bite lasting up to 10 days.

Fishing Spiders

Occasionally fishing spiders (Dolomedes species) wander into Iowa homes from adjacent lakes, rivers, streams, or ponds. These large, semi-aquatic spiders measure up to 2 inches long with brown and gray striped designs on their hairy bodies. They rely on stealth and speed to capture prey near water rather than spinning webs.

Despite having sizable fangs, fishing spiders rarely bite humans unless severely threatened. And while their venom can penetrate the skin, it poses little medical significance beyond temporary pain and redness at the bite site. Their jaws are usually too small and weak to inflict serious harm on people.

Crab Spiders

Crab spiders comprise many genera and species found throughout Iowa. These stealthy ambush hunters often invade homes while hunting insects. They come in brown, white, yellow, and green color variations to blend with flowers where they wait unseen for bees, butterflies, and flies to pass by close enough to grab.

Bites typically happen when spiders get trapped against bare skin or while putting on clothing harboring a hiding crab spider. Fangs do break the surface and release venom, though effects are usually limited to mild pain and swelling around the wound. Some localized itching, numbness, or blistering might also occur.

spiders that bite danger

Out of over 650 species of spiders that inhabit Iowa, only a couple pose a serious health threat to humans if they bite and inject their venom. Knowing how to identify them allows homeowners to take proper precautions in areas of the home these venomous spiders occupy.

Brown Recluse Spiders

The brown recluse spider (Loxosceles reclusa) hides in dark, secluded spaces within homes like attics, crawlspaces, cellars, closets and sheds. Their venom destroys cell membranes and can cause severe reactions when it diffuses through human tissues. But bites happen rarely and only when these nocturnal spiders get trapped or crushed against bare skin.

This species measures roughly half an inch long with a dark brown body and yellowish-gray marking on the abdomen that resembles a violin. People bitten suffer flu-like symptoms along with severe pain, itching, nausea, and joint stiffness. The bite site ulcerates into a painful slow-healing lesion in severe cases that sometimes requires surgical intervention.

Black Widow Spiders

The venomous black widow spider (Latrodectus variolus) spins messy-looking cobwebs in dark isolated spaces around homes like garages, sheds, wood piles, or crawlspaces. Adult females have shiny black rounded abdomens with a prominent red hourglass marking. They measure just shy of 12 inch but pack potent neurotoxic venom.

Black widow bites often go unnoticed at first since they do not hurt initially. But painful muscle cramping, nausea, and profuse sweating around the bite site start within a few hours. Though rare, bites can progress to paralysis or unconsciousness if not treated promptly with antivenom containing spider antitoxin as the preferred first-line treatment.

Precautions for Venomous House Spiders

The brown recluse and black widow spiders have established populations throughout Iowa. So precautions are necessary when entering garages, basements, cellars, sheds and other isolated areas within homes where these venomous spiders reside undisturbed.

Protective Clothing & Eyewear

Wearing gloves, long sleeves and pants reduces the risks of accidental bites from venomous spiders. Tuck cuffs into gloves and boots as added protection. Also consider goggles or safety glasses when entering crawlspaces or while brushing aside debris near structures.

Insecticide Treatment

Applying residual insecticides like deltamethrin, lambda cyhalothrin or permethrin around the perimeter of homes helps discourage black widows and brown recluses from taking up residence. Spot treatments directly into cracks, crevices, weep holes or openings spiders exploit to enter helps reduce populations on a larger scale.

Remove Clutter & Debris

Keeping areas around the homes foundation clear of debris like stacks of wood, piles of rocks and excess junk eliminates shelter sites sought out by venomous spiders. Trimming vegetation back improves visibility and removes protective hiding spots as well.

Professional Inspections

Having a qualified exterminator thoroughly inspect garages, sheds, attics, basements and crawlspaces helps identify established black widow and brown recluse populations. Professional chemical treatments work faster at eliminating infestations before spiders spread deeper into living spaces.

While most spiders found inside Iowa homes present no safety hazard, the venomous black widow and brown recluse spiders warrant caution. Understanding where these spiders hide and implementing some simple precautionary measures greatly minimizes bite risks around properties.

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a healthcare professional before starting any new treatment regimen.