Venomous Spiders in Crawlspaces and Sheds
Why this matters
The places trade techs reach into without looking are the places two medically significant spiders prefer: the meter box, the irrigation valve box, the AC disconnect, the crawlspace vent, the shed where the customer keeps the spare filters, the glove that sat in the truck's side compartment all week. Both spiders are shy and bite only when pressed against skin, so nearly every bite is a reach or a dressing mistake. Most bites heal without lasting harm. A few send a tech to the emergency room with full-body muscle cramps, or leave a slow-healing wound. The protection is gloves, a flashlight and a shake. The failure is a bare hand into a dark box.
The two that matter in the US
Widow spiders (the southern, northern and western black widows, plus the invasive brown widow in the South and California) live across nearly the whole country. The female is glossy black, round-bodied, with a red or orange hourglass on the underside; the northern species often shows a broken hourglass, and the brown widow is mottled tan with an orange hourglass. Their web is the giveaway: an irregular, tangled, unusually strong web close to the ground, often with a funnel or retreat toward the back. Widows prefer dark, sheltered spots near the ground and outdoors: woodpiles, meter and valve boxes, the underside of outdoor furniture, crawlspace vents and access doors, garden sheds, stacked lumber or block, the inside of electrical enclosures and pool equipment housings, the rim of an overturned bucket.
The brown recluse has a narrower range: the south-central and lower Midwest states, roughly from Nebraska and Texas east through Missouri, Arkansas, Oklahoma, Kansas, Tennessee, Kentucky, and into parts of the Gulf states and the lower Ohio valley. Related recluse species live in the desert Southwest. It is uniformly tan to brown with a darker violin-shaped mark on the front body section, the neck of the violin pointing toward the abdomen, uniformly colored legs, and, the reliable mark, six eyes in three pairs instead of the eight most spiders have. It is a hunter, not a web-sitter, and hides in dry, undisturbed clutter: cardboard boxes, attics, closets, the folds of stored clothing, shoes and gloves left in a garage or shed.
Where the range lines matter: outside the recluse's range, a "brown recluse bite" is almost never one. CDC and university entomologists have documented that many wounds blamed on recluses outside their range turn out to be bacterial skin infections, including MRSA, which need different treatment. A tech in Maine with a sore red lesion should not let anyone, themselves included, close the case with "spider bite."
The ones that are not the problem
- Wolf spiders: large, fast, alarming, and a painful but medically minor bite.
- Hobo spiders in the Pacific Northwest: long reputed to cause wounds like a recluse; later research has not supported it.
- Yellow sac spiders: common indoors, a minor and occasionally irritating bite.
- Daddy longlegs of either kind: harmless to people, whatever the playground story says.
Treat any bite with the same first aid; reserve the urgency for widow symptoms, recluse range, or a wound that is getting worse.
How the bites happen, which is how they are prevented
Neither spider chases. Bites come from trapping one against skin: a hand closing on it in a box, a foot going into a boot it is sheltering in, a glove pulled on over it, a back rolled onto it in a crawlspace, coveralls pulled up over one that crawled into a pant leg. That mechanism makes prevention very concrete.
Light it before you reach into it. Every meter box, valve box, disconnect, crawlspace vent and equipment cabinet gets a flashlight look before a hand goes in. A widow web is easy to see once you are looking.
Clear webs with a tool, and pick the right tool for the box. In a valve box or a woodpile, a stick or a long screwdriver is fine. Inside an electrical disconnect or panel, the line side stays energized even with the disconnect open, so a widow web over the terminals is cleared with a dry, non-conductive brush or stick held clear of the lugs, never a metal screwdriver and never a gloved hand swatting at it. If the web or spider is on or behind energized parts, leave it for after the circuit is dead and proved dead.
Gloves for anything you cannot see into. Leather or heavy work gloves for reaching into boxes, lifting stored material, moving firewood or stacked block, and handling the customer's shed contents. Nitrile alone will not stop a bite.
Shake out what has been sitting. Gloves, boots, coveralls, knee pads and jackets stored in a truck compartment, a garage or a shed get shaken out and looked into before you put them on. Store them in a closed bin rather than hanging open in a side box.
Crawlspaces: dress for it. Long sleeves, pants tucked into boots, gloves, and a slow light sweep of the space before entering and as you move. Look at overhead joists and the area around vents and the access door, where widows are most common. The full crawlspace pre-entry check is its own procedure. See related: The Crawlspace Entry Hazard Check SOP.
What a bite looks like, and what to do
Widow bite. Often felt as a pinprick or not at all. Within about an hour, pain spreads from the bite, followed in some people by muscle cramps and rigidity, especially in the abdomen, back or chest, with sweating, nausea and a racing heart. A rigid belly from a widow bite has been mistaken for appendicitis, which is one more reason to tell the clinician what happened. Deaths in healthy adults are rare, and an antivenom exists for severe cases.
Recluse bite. Usually painless at first. Over the following hours a red, sore area develops, sometimes with a blister; in some bites the center darkens and a slow-healing ulcer forms over days. Most recluse bites heal without major complications. Rarely, and more often in children, the venom causes body-wide effects such as fever or the breakdown of red blood cells, which is why a recluse bite with fever is an emergency visit.
First aid, following NIOSH's guidance for workers:
- Stay calm and move away from the spider.
- Photograph the spider if it can be done without a second bite, or bring it in a sealed container if it is already dead. Identification changes how the clinician thinks.
- Wash the bite with soap and water.
- Apply a cool compress: a cloth soaked in cold water, or ice wrapped in cloth, not ice straight on skin.
- If the bite is on an arm or leg, elevate it.
- Get medical care, right away for a suspected widow or recluse bite or any spreading pain, cramps, fever or worsening wound.
Do not cut the bite, try to suck out venom, or apply a tourniquet. None of them help, and the cut adds a wound.
Worked example: a September service call in Missouri
An HVAC tech and a helper are servicing a condensing unit beside a backyard shed in central Missouri, inside both the widow's and the recluse's range.
The disconnect. Before opening the AC disconnect enclosure on the wall, the tech puts a light through the gap in the cover and sees a dense, tangled web across the bottom of the box and a black widow tucked at the back corner, behind the line-side terminals. The disconnect pullout comes out, which kills the load side, but the line side is still live, and the spider is beside it. The tech does not reach in. He shuts off the AC breaker at the panel, locks and tags it, and proves the line terminals dead with a meter proved on a known live source before and after (NFPA 70E-2021, 120.5; OSHA work practices at 29 CFR 1910.333(b)(2)). With the box dead, the web and spider are cleared out with a long dry brush. Cover back on first, then the lock and tag removed, then the breaker closed with the tech standing to the side of the panel rather than square in front of it. About seven minutes added to the call.
The shed. The customer keeps a spare filter set in the shed. The tech puts on leather gloves, lights the shelf, and lifts the cardboard filter box by its outside edges rather than reaching in. Nothing found.
The bite. Halfway through, the helper pulls a pair of coveralls from the truck's open side compartment, where they had hung for a week, and steps into them. He feels a sharp sting on the back of his left thigh. He unzips at once and finds a small tan spider, crushed, in the pant leg. Phone photo, zoomed: a dark violin mark, and, under magnification, eyes in pairs.
The response. The helper washes the spot with soap and water from the truck jug and holds a cold wet rag on it while the tech calls the office. The bite is a faint pink spot, painless after the first sting. Because this is recluse country and the photo looks like one, the office sends him to urgent care that afternoon with the photo and the time of the bite, rather than waiting to see. The clinician examines it and gives instructions on what to watch for. By the next morning the area is red and about an inch across, the clinician's follow-up the day after says it is healing, and it resolves over the next two weeks. The office records the bite with date, time, the photo, and where the coveralls had been stored.
What changed afterward. All crew coveralls and gloves now live in closed plastic bins in the truck, not hanging in an open compartment. That fix took one afternoon and would have prevented the bite entirely.
What would have changed the answer: the same pink spot on a tech in a northern state, with no spider found, gets watched, not rushed. If it turns into a painful, spreading, pus-filled lesion over a few days, the clinician hears "possible skin infection, no spider seen," not "spider bite."
References
- NIOSH, Venomous Spiders (species, prevention for outdoor and indoor workers, first aid)
- CDC, information on widow and recluse spider bites and the misattribution of skin infections to spider bites
- OSHA, 29 CFR 1910.333 Selection and Use of Work Practices; NFPA 70E-2021, 120.5 (verifying absence of voltage)
- See related: The Crawlspace Entry Hazard Check SOP
- See related: Snakes Under Houses and Inside Equipment