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Hobo spiders (Eratigena agrestis) are venomous, but current evidence does not support treating them as a significant danger to people. Bites are uncommon, the spiders are not aggressive, and the claim that their bites cause “flesh-eating” wounds is not supported by strong evidence. If you find a spider near a skin lesion, that alone does not prove it caused the injury; seek medical advice if symptoms worsen or persist.
Are hobo spiders venomous or dangerous?
Hobo spiders have venom, as spiders do, but venomous does not automatically mean medically dangerous. Current university and state guidance does not consider the hobo spider a probable medical danger to people. A bite is possible, but available evidence describes bites as rare or unlikely—not as a common or established cause of severe injury. Utah State University Extension describes the spider as nonaggressive and unlikely to bite, while the University of California Statewide Integrated Pest Management Program says it is no longer considered of probable medical importance.
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That is a qualified assessment, not a promise that a bite could never happen or that every skin reaction is harmless. If someone develops worsening inflammation, persistent soreness, or other concerning symptoms after a suspected bite, contact a health professional. The practical takeaway is to avoid handling the spider, avoid assuming it caused a wound, and get expert identification when the species matters.
Can a hobo spider bite cause a “flesh-eating” wound?
The evidence does not support the widespread claim that hobo spider bites routinely cause necrotic, or tissue-damaging, wounds. The reputation grew from a U.S. designation in the 1980s and reports of suspected severe cases, but later research and reviews questioned whether hobo spiders were responsible for those injuries. UC IPM’s current account says the spider is not considered of probable medical importance.
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The timeline helps explain why sources can sound contradictory. A 1996 CDC report discussed suspected cases in the Pacific Northwest, including skin lesions and systemic symptoms. It is historical context, not a current estimate of how often bites happen; its authors said reliable estimates of bite incidence and medical-attention frequency were unavailable. Later university extension assessments do not substantiate a significant necrotic-bite risk.
UC IPM describes a 2004 editorial that found one verified hobo-spider bite associated with a necrotic lesion. The person had a pre-existing condition that can also cause necrotic lesions, so the case does not establish that the spider caused the tissue damage. UC IPM also describes a verified bite reported in Oregon in 2014: pain, some redness, and leg twitching lasted 12 hours before resolving. These are individual cases, not a rate of risk or proof that hobo bites commonly cause those effects.
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Why are hobo spiders called aggressive?
Hobo spiders are described by extension sources as nonaggressive; the old nickname “aggressive house spider” is misleading. Montana State University Extension and Utah State University Extension explain that the word agrestis refers to a field or rural habitat, not an aggressive temperament. The nickname arose from a mistaken interpretation of the scientific name.
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Like other spiders, a hobo spider may bite defensively if trapped against skin or handled, but it is not generally described as seeking out people. Utah State Extension says a defensive bite may cause mild pain and redness. A spider wandering indoors—or being found in the same room as someone who later notices a skin problem—does not by itself show that it bit anyone.
How can you identify a hobo spider?
Identifying a hobo spider reliably can be difficult, especially from a casual look or a photograph. Many spiders resemble it, and UC IPM cautions that non-specialists are unlikely to identify it correctly by sight alone. When certainty matters, ask a local extension office or arachnology expert rather than relying on a large brown spider’s appearance.
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The accepted scientific name used by current extension sources is Eratigena agrestis; older literature may call it Tegenaria agrestis. UC IPM says reliable identification in California often depends on examining reproductive features. A hand lens or microscope can help inspect features such as eye arrangement, but close visual inspection does not guarantee a correct identification by a nonexpert.
Range is another reason not to guess. Utah State Extension says the species is native to Europe, was detected in the Pacific Northwest in 1936, and is now found in parts of the western United States, including northern Utah. UC IPM describes a broad Pacific Northwest and western range, but says California records have not been verified by a qualified arachnologist. A funnel-shaped web or a large brown spider is not enough to establish that it is a hobo spider.
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Utah State Extension notes that hobo spiders and related spiders build funnel webs. It also reports that hobo spiders are frequently found in Utah homes from August through October, when males search for females. That timing is specific to Utah guidance; it should not be assumed to describe every region.
What should you do if you think a hobo spider bit you?
Clean and cover the area, watch for changes, and contact a health professional if symptoms worsen, the area becomes inflamed, or soreness persists. If you can safely preserve the spider, a local extension or arachnology expert may be able to identify it; do not risk another bite trying to catch it.
- Do not assume the spider caused the mark. A spider found nearby after a skin irritation appears is not proof of a bite. The CDC’s general spider guidance warns that wounds and infections are often attributed to spider bites when no spider was seen or identified.
- Clean and cover the suspected bite. Utah State Extension advises cleaning and disinfecting the area and covering it with a sterile bandage.
- Monitor how it changes. Seek medical advice if symptoms progress. Montana State Extension also recommends medical care if the wound becomes inflamed or soreness persists; a secondary infection can follow bites or scratches.
- Save identification evidence only if it is safe. A specimen may help an expert identify the spider, but do not handle it with bare hands or put yourself at risk to obtain one. A clear photo may be useful to an expert, though it may not be enough for a definitive identification.
This guidance is not a diagnosis. A worsening skin lesion can have causes other than a spider bite, and a clinician can assess symptoms that need treatment. If the person has severe or rapidly worsening symptoms, seek urgent medical help rather than waiting for a spider identification.
What does the evidence say about how often hobo spiders bite?
There is no reliable incidence figure in the sources reviewed, so it is not possible to give a defensible percentage or annual bite rate. The CDC’s 1996 report explicitly noted that reliable estimates of how often bites occurred—or how often people sought medical care—were unavailable. UC IPM reports very few verified bites, but that does not provide a population-level rate.
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When assessing claims about hobo spiders, distinguish four things: when the evidence was published, whether the spider was positively identified, whether the reported outcome was verified, and whether the source describes one case or a general risk. A historical suspected case and a confirmed individual bite do not, by themselves, show how likely a bite is or how dangerous it is for the average person.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Do hobo spiders pose a danger to pets?
The evidence summarized here addresses human bite risk and does not establish a hobo-spider-specific level of danger to pets. Do not infer from a spider’s presence that a pet has been bitten. If you suspect an animal has been bitten or it develops concerning symptoms, contact a veterinarian for advice rather than trying to diagnose the cause from the spider’s appearance.
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What is the sensible response to a hobo spider at home?
For most people, the evidence supports caution rather than alarm. Avoid handling an unidentified spider, and seek help with identification if you need to know the species. The available evidence does not establish a reason to treat every hobo spider sighting as a medical emergency or to make a pesticide purchase solely because the spider might be a hobo spider.
Keep the distinction clear: a spider’s venom makes it venomous, but that fact alone does not establish a meaningful medical threat. Current extension guidance describes hobo spiders as unlikely to bite and not of probable medical importance, while acknowledging that a suspected bite should be monitored and worsening or persistent symptoms deserve professional advice.
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Frequently Asked Questions
Are hobo spiders found in California?
California reports have not been verified by a qualified arachnologist, according to UC IPM. That uncertainty is one reason not to identify a spider from a general location or appearance alone.
Does seeing a hobo spider mean it caused a skin sore?
No. A spider’s presence near a sore does not establish that it bit someone, and the CDC warns that infections and other wounds can be mistaken for spider bites when the spider was not seen or identified.
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The concern traces in part to a U.S. designation in the 1980s and suspected cases reported in the Pacific Northwest. Those older claims need to be read alongside later reviews and extension guidance, which question a significant necrotic-bite risk.
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