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Black Widow Spiders Are Wasteful Gluttons

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The most venomous spider in North America, the black widow, is actually a bit of a couch potato.

“They’re sort of like humans, when they’re around a lot of food they become lazy and wasteful,” said J. Chadwick Johnson, a biologist at Arizona State University. “They’ll kill food they don’t need, and leave some of it uneaten.”

Johnson’s team describes the spiders’ habits in a paper called “Wasteful Killing in Urban Black Widows: Gluttony in Response to Food Abundance,” published online Jan. 17 in the journal Ethology. Wastefulness is strange to see in animals, because hunting involves spending energy, risking injury and killing prey that might be needed later.

Other research from Johnson’s lab has shown that black widows can inherit some feeding tendencies, such as a taste for cannibalism, from their parents. For this study, they wanted to see if wasteful killing was a product of a spider’s individual traits, or if most black widows — which, when they’re not being wasteful, can go two months without eating — behave the same way.

In the lab they fed crickets to spiders, then measured how much the spiders ate. Some of the spiders hadn’t eaten in two days; others had gone without food for 7 or 14 days. Johnson’s team found that the spiders were quicker to attack and ate more food when they’d gone longest without eating. Habits in individual spiders, which would suggest a genetic component of gluttony, didn’t show a trend.

“The spiders are more aggressive when they’re hungrier,” Johnson said. “The simplest explanation is that.”

It isn’t clear if this kind of feeding is adaptive for the spider, but it might be a way of attracting mates. Other studies show that male black widow spiders are attracted to the smell of well-fed females.

“Even if she’s not around her web, he’ll get turned on and begin courting like crazy,” Johnson said.

If a male black widow chooses to mate with a starving female, he risks becoming a post-nuptial snack. Johnson speculates that females might be advertising for males by leaving wasted food in their web.

It sends a signal: “Come hither, because I won’t kill you.”

Image: Female black widow spider, Latrodectus mactans. (James Gathany)

See Also:

Citations: “Wasteful Killing in Urban Black Widows: Gluttony in Response to Food Abundance.” By Patricia Trubl, Valerie Blackmore and J. Chadwick Johnson. Ethology, Vol. 117, Issue 3, March 2011.

The most venomous spider in North America, the black widow, is actually a bit of a couch potato. “They’re sort of like humans, when they’re around a lot of food they become lazy and wasteful,” said J. Chadwick Johnson, a biologist at Arizona State University. “They’ll kill food they don’t need, and leave some of […]

Common Spider Species: Black Widow

Black widow spiders are greatly feared by many, and perhaps rightly so; they are considered the most venomous spider in North America. The black widow’s other nightmarish claim to fame is the macabre tendency of the female spiders to eat their male suitors after mating. Indeed, this courtship ritual is the reason why these spiders were given the name “black widow.”

Appearance

Black widow spiders are easily recognizable. They have plump, shiny black abdomens that bear an hourglass-shaped red, red-orange or yellow mark. Black widows weave erratic sticky webs that lack any shape or form. Their silk is stronger than virtually all other spiders. Other distinguishing features of the black widow spider include:

  • Female black widow spiders are 1/2 to 1 1/2 inches long. Males are about half the female’s size, with smaller bodies and longer legs
  • Females usually have a reddish hourglass shape on the underside of their abdomens. In some species, the females have a series of red spots and two crosswise bars on the underbelly
  • Male black widows often have yellow and red bands and spots on their backs, as do both sexes of black widows in their immature stages
  • Newly hatched spiders are predominately white or yellowish-white, gradually acquiring more black and varying amounts of red and white
  • Juveniles of both sexes resemble the male and are harmless to humans

Habitat

The black widow spider is shy and nocturnal, usually staying hidden in its web, hanging with its belly upward. Although not aggressive by nature, a black widow spider may bite when its web is disturbed.

The black widow is commonly found outdoors in woodpiles, rubble piles, hollow stumps, rodent burrows, sheds, garages, and under stones. Indoors, they generally seek out cluttered areas in basements and crawl spaces.

Geography

Black widow spiders are found in temperate regions throughout the world. In the United States, they exist primarily in the southern and western states. Black widow spiders are typically found outdoors, though they may move indoors in colder weather.

Black widow spiders feed on the prey that have the bad luck to get caught in their strong, silken webs. Besides eating other arachnids, black widows enjoy a varied diet of insects including mosquitoes, ants, flies, beetles, scorpions, grasshoppers and caterpillars. After ensnaring their prey, black widow spiders use their hind comb feet to wrap their victims in silk before injecting them with digestive enzymes that liquefy the corpses. The spider then sucks up the resulting fluids.

Threat

Considered the most venomous spider in the United States, the venom of a female black widow spider is 15 times as toxic as the venom of a rattlesnake. Fortunately, black widows only bite when disturbed, and contrary to popular belief, most victims do not sustain serious harm. Though rare, their bites can be fatal, with young children, the elderly and infirm at highest risk. If you suspect a black widow bite, get medical help as soon as possible.

The black widow’s venom is neurotoxic, meaning it directly affects the nervous system. Telltale signs of a black widow bite include:

  • One or two bite marks on the skin, with local swelling
  • Pain that moves from the bite site to the abdomen and back
  • Cramps, muscle aches, rigidity, profuse sweating, nausea, fever and a paralysis of the diaphragm that can make breathing difficult

Pain from a black widow spider bite will usually persist for the first 8-12 hours, though symptoms may continue for several days.

Control Options

Considering the fact that black widow spiders are one of the most dangerous spiders in the United States, you’ll want to protect yourself from these creepy (and potentially deadly) crawlers by fortifying both the inside and the outside of your home.

Indoors, place TERRO ® Spider and Insect Traps in high spider traffic areas: along baseboards and foundation cracks, behind doors, and near windowsills and other arachnid-friendly hangouts. When a black widow spider wanders onto the trap’s sticky surface, it will get stuck and die.

Next, you’ll want to head outdoors with a can of TERRO ® Spider Killer Spray in hand, spraying areas where black widows like to hang out, such as woodpiles, heaps of dead leaves, garages or anywhere debris builds up. The spray not only works to kill spiders instantly, but it also provides residual control for weeks. So go to town and create a barrier around your house, reducing the likelihood of a dangerous and unwanted guest coming in.

Learn about Black Widow Spiders including how to identify them by appearance, habitat and diet, as well as control options suitable for Black Widow Spiders.