Wild Ideas: Black widow or not?

Top photo by Paul Sapiano via Wikimedia Commons; bottom by Brenda Clement Jones/Old Rag Master Naturalists.
While the typical southern or western black widow adult female (top photo) is all black on top and has the famous red hourglass marking underneath, females in the northern black widow species have a white-rimmed row of red spots running down the back (bottom). The northern species also has two unconnected red triangles on its underside, while in the southern species the triangles are connected into an hourglass shape. Top photo by Paul Sapiano via Wikimedia Commons; bottom by Brenda Clement Jones/Old Rag Master Naturalists.

Nature often seems to show a disdain for simplicity, which can complicate our attempts to identify species, even those we think we know very well. This issue was brought home recently when a member of my master naturalist chapter posted a photo to our email list of a spider whose species she was trying to determine.

The hunched, fat, hairless body of the spider made me think of a black widow immediately, but the coloring didn’t jibe with photos I’d seen or descriptions I’d read, and I haven’t observed black widows in the flesh. While this spider was mostly black, that was broken up by bright white and orange markings.

I’ve learned over the years that many species take on different colors and even shapes at various points in their development; their shapes and colors can also vary by gender. I remembered reading somewhere that juvenile black widows can have very different coloring, so I started looking for photos of black widows at all stages of their lives. I found there are actually several species of black widows, and the coloring can indeed vary among species, genders and ages.

I finally tracked down descriptions and photos of juvenile black widows, including those of the two species most common here in Virginia, the southern black widow (Latrodectus mactans) and northern black widow (Latrodectus variolus). The distinctive red hourglass shape on the underside of the female’s abdomen that we associate with widows is instead two unconnected triangles on the northern species, particularly younger females, according to the Virginia Cooperative Extension (VCE) website.

The northern females also typically have a line of white-rimmed red dots that run down the middle of their backs. The spider in the bottom photo on this page, with its bright white and orange markings, matched photos of juveniles of the northern species.

The southern black widow females are between an inch and an inch and a half long, while the northern females are smaller, about a half-inch long. The males are typically about half the size of females or even smaller and have more elongated bodies.

Another way to identify black widows is by their webs, which are messy. As the University of Virginia Health System website puts it, “The pretty, two-dimensional web like the one in Charlotte’s Web is not a black widow web.” The site also notes that black widows move fast in their webs but are much slower on the ground.

Widow spiders tend to like quiet, dark, undisturbed places, especially piles of wood or rocks. They can occasionally show up inside, usually in attics, basements and garages.

According to VCE, widow spiders are non-aggressive but can bite if touched. Only adult females carry venom, which affects the nervous system and “is one of the few medically significant venoms possessed by a spider in North America.” It can cause a reaction in humans that varies in intensity depending on the health and age of the person bitten, but death occurs in less than one percent of victims.

Widow spiders got their name undeservedly, according to the VCE website. While in early lab studies females were observed killing their mates after mating, the spiders were kept in confining containers, and the males were trapped in the females’ webs. The females likely perceived the males as a threat. Subsequent studies showed that when males can leave the web after mating, they do, and the females typically let them.

As I started bringing in wood to feed my wood stove this fall, I thought back to when I was a kid and was taught to avoid black spiders and wood piles. In bringing wood in now, I wear gloves and look carefully at each log as I pick it up. I then knock the log against the ground or another hard surface to try to dislodge any spiders or insects that may be taking shelter on it.

I love bugs. I even love spiders. But I’m not keen on having either in the house, especially if they’re venomous.

What about the other spider that is often the subject of fear here in the Old Dominion, the brown recluse? It’s become “almost a source of urban legend,” which has led to “a lot of paranoia and misdiagnoses,” says the UVA site. While an occasional one can show up, the brown recluse is not native to Virginia and doesn’t like our climate. Even where it is common, humans are rarely bitten, since the spider is “very shy,” says the site. However, the bite of some brown spiders that are native to Virginia can mimic the bite of the recluse, including producing methicillin-resistant staph infections.

The VCE website offers a lot of interesting factoids about widow spiders, but the following one made me even more thankful for modern plumbing: “Historically, outhouses were the primary locations where humans would experience the dreaded widow spider bite. Attracted to the dark, warm area with numerous flying insects, the widow spiders would often nest in the gap beneath the toilet seat. This situation proved particularly dangerous for men!”

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Pam Owen
About Pam Owen 274 Articles
Writer, editor, photographer, and passionate nature conservationist living in Rappahannock County, in the Blue Ridge Mountains of Virginia. Two favorite quotes: By E.O. Wilson, who coined the term "biodiversity," "Nature holds the key to our aesthetic, intellectual, cognitive and even spiritual satisfaction”; by Douglas Adams, “I love deadlines. I love the whooshing sound they make as they pass by.”