Southern Black Widow Spider, Vol. 6, No. 32

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October 14, 2020

Latrodectus mactans

Order: Aranea
Family: Theridiidae

Black widow! Most people experience an involuntary startle response when they first encounter a black widow spider while working in the yard or garden. Depending on the situation, and the person, this response ranges from mild to quite dramatic, but it is real, an internal jumping sensation, like seeing a snake. We humans have an instinctive fear of venomous animals, and that red hourglass shape on a shiny black background is so iconic. Black widow!

Once we recover from this initial surprise, most of us quickly realize this particular spider is not much of a threat. We know where it is, and we can easily avoid it. We can even kill it if we wish. But this can lead to more questions. Just how dangerous are black widow spiders? Are there more? What precautions should I take to avoid being bitten?

While black widows are one of the few seriously venomous spiders in the US, the number of fatalities caused by black widows is surprisingly low. During the eight-year period 2008-2015 there were an average of 6 fatalities per year in the US due to all venomous spider bites, but it is unclear how many of these were due to black widows. This is considerably less than the annual number of fatalities caused by more dangerous animals such as dogs, 34 deaths per year; horses, cows and other large mammals, 74; and stinging insects, 60 fatalities per year. Notably, venomous snakes only caused an average of 6 deaths per year during this period, the same as spiders. Based on the past 10 years of reports from the National Weather Service, lightning has caused an average of 26 fatalities per year.

How many people are bitten by black widows each year in the US? A 2001-2005 study found an average of 2663 black widow spider bites were reported to US Poison Control Centers each year, but only 830 sought treatment at health care facilities and none were fatal. Black widows are not aggressive and usually flee from danger when possible. Most bites occur when someone unknowingly sticks an unprotected hand into a web, or when a spider is inadvertently crushed against the body when moving debris, harvesting produce, or preforming other outdoor activities.

Black widows rarely occur indoors, preferring to build their webs near the ground in dark, protected areas such as piles of debris, lumber or trash. Water meter housings, hollow concrete blocks and overturned flowerpots are favorite sites, and they often nest near the ground in growing plants: the base of a shrub, under vegetable vines, in potted plants and similar settings. Populations vary from year to year. Some years it is difficult to find even one; other years they seem to be in almost every suitable nesting site.

Control: Insecticides are not very useful against black widows. The best way to limit the number of black widow spiders around the house is to limit potential nesting sites by removing debris, piles of limbs, stacks of lumber, and similar items. Wear gloves when doing this, and when performing similar outdoor activities and you will greatly reduce your, already quite low, chance of being bitten—or getting a bad splinter.

See Extension Publication 2154, Spiders, Brown Recluse and Black Widow for more information on black widow biology and control.

Annual fatality statistics from J. A. Forrester, et. al., 2018, An Update on Fatalities Due to Venomous and Nonvenomous Animals in the United States (2008–2015), Wilderness & Environmental Medicine (2018): 29, 36-44.

Final Article of the Season: This is the last article for 2020, but Bug’s Eye View will be back next spring.

Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service.
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