Which spiders in the U.S. are venomous? — Emily’s student essay

Which Spiders in The U.S Are Venomous?

It’s likely that you or someone you know has a fear of spiders, and for very understandable reasons. Perhaps it is due to their numerous long and spindly legs, or their fast speed, or it may be for the scary possibility of being bitten. Although arachnophobia tends to be a common fear, there are actually just a handful of spiders that are considered venomous. Spider venom has evolved to help spiders take down smaller prey items such as insects and is generally not well adapted to causing serious harm to larger mammals. On average, 4 people per year have died from a venomous spider bite. The development of antivenom has made the number of fatalities from spider bites very rare. However, there are a couple notable genus’ of spiders that are worth keeping an eye out for as their bites may prove to be very nasty.

Widow’s, also known as the Latrodectus genus, are found across the globe and may be found in North America as well as in Hawaii. They are fairly small, averaging at about 8—13mm (.31—.51”) and are normally dark brown or shiny black. Females are known to have the notorious red or orange hourglass on their underside while males tend to have red spots and a pair of white strips on their topside. These spiders tend to make their homes in cluttered undisturbed areas, normally in small holes, the underside of furniture, wood piles, or construction sites.

 If you do happen to be bit by a widow, you may experience systemic effects known as latrodectism. These symptoms include muscle pain, abdominal cramps, increased sweating, increased heart rate, and muscle spasms. Death from a widow’s bite is a very unlikely occurrence, as there have been no deaths recorded since 1983, as reported by the American Association of Poison Control Centers.

Black Widow

Next on this list are recluse’s (Loxosceles genus), also known as brown spiders, fiddle-backs, violin spiders, and reapers. These are found worldwide as well, but mainly tend to be found in warmer climates. They are known to live within a 2000 km radius from the center of Arkansas, which includes south-eastern Nebraska, Kansas, Oklahoma, Texas, Louisiana, Arkansas, Missouri, Kentucky, Tennessee, Mississippi, Alabama, northern Georgia, southern portions of Ohio, Indiana, Illinois, and Iowa. Unlike widow’s, their appearance varies amongst different species. Some recluse’s are known to have a violin shape on their cephalothorax, however this is not a reliable characteristic to use in identifying a recluse since some species do not bear this marking and many species outside of the Loxosceles genus do bear this marking. They typically measure about 6—20mm (.24—.79”) long. They prefer the same habitats as a widow and are known to be rarely aggressive. They usually bite only when pressed against skin, such as when they are stuck underneath clothing. A recluse’s bite may induce loxoscelism, which includes nausea, vomiting, fever, rashes, and muscle and joint pain. A minority of bites may result in a necrotizing ulcer due to soft tissue destruction and will eventually slough away, leaving permanent scarring. While there are deaths reported from brown recluse bites, the most common recluse in the US, these tend to mainly be in children under the age of 7 or those with a weak immune system.


Lastly, we have the hobo spider (Eratigena agrestis), a member of the funnel-spider genus. Because they originate from Europe and were introduced to the US through shipments, they are found only in western North America, but may also be found in Central Asia as well. They range in length from 7—16mm (.28—.63”) and are brown with several chevron shaped markings on their abdomen. 

They prefer to make their homes in undisturbed areas on the ground away from civilization and generally aren’t very good climbers. While hobo spiders are known to be a bit more aggressive and relatively fast (reaching speeds of 3 feet per second), they are actually not considered venomous by the Center of Disease Control. Many bites which were reported to have been from a hobo spider are suspected to actually have been from a brown recluse, contributing to their bad reputation. In addition to this, there is little evidence that a hobo spider is actually dangerous. The bite from a hobo spider may cause redness and itching, but is otherwise not venomous or deadly. This spider is worth mentioning, however, since there is much misconception surrounding this species.

If you or someone you know is fearful of the effects from a spider bite, you may rest easy knowing that death is an extremely unlikely possibility, with the second worst effect being an ugly scar, which is still a very unlikely possibility! However, one should still be sure to exercise caution when interacting with what may possibly be the home of a spider, just to be on the safe side.

Author: Emily Rodriguez

University of Arizona
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