This Creature Can Feast on Black Widows and We Now Know How

Researchers in Nevada have taken one step closer to identifying the secret to resisting the venom of the black widow spider. By studying the effects of the venom on lizard species that are the spider's natural predators, the team found that they could resist the spider's deadly defenses.

"When I was a wee graduate student, I read that alligator lizards could eat black widows," Chris Feldman, who led the Nevada research, told Newsweek. "But no one had bothered to investigate whether they might actually be resistant to the venom."

Black widow spiders, distinguished by their shiny black bodies and red hourglass markings, are one of the most venomous spiders in North America. However, their bite is rarely fatal to humans.

"An individual spider doesn't contain enough venom to kill a human," Feldman said. "Black widow spiders prefer to hide from people, so bites are quite infrequent in the U.S. Very small children and the elderly can develop more severe illnesses requiring medical attention, but human deaths are very rare."

A bite can result in severe muscle pain and cramping, nausea, and mild paralysis of the diaphragm, making it difficult to breathe.

"The venom is a fairly sophisticated and complex mixture of proteins that target motor neurons and muscle cells," Feldman said. "The venom causes muscles to rapidly twitch, until they eventually lock up and seize, which is quite painful. And then the venom causes muscle necrosis, where the muscles actually die—also painful.

"While this would be a painful nuisance to us, to a small animal, the effects might be very dramatic."

In Feldman's study, published in Royal Society Open Science on October 19, he and his team at the University of Nevada, Reno, tested how the venom of the black widow affected two lizard species known to prey on the spiders—the alligator lizard and the western fence lizard. The team injected them with the deadly venom and set them on a miniature race course to measure their physical performance.

The animals were also tested for muscle damage and immune activity. These results were compared with those of a potentially susceptible lizard species, known as prey of widows.

"When we did our first trials … those alligator lizards were unfaceted, even at doses that should have been five times the lethal dose," Feldman said. "The most surprising part was the muscle histology results. The muscles of the alligator lizards show no impact of the venom. In fact, the injected muscles look so similar to un-injected muscles that at first we thought we'd made some mistake with our samples."

In comparison, the susceptible species showed significant performance reduction, increased muscle damage and considerable immune activity in response to the venom. This indicates that the alligator lizard has evolved some sort of resistance.

"These kinds of chemically mediated predator-prey interactions are all around us," Feldman said. "Classic examples include poisonous newts and their resistant garter snake predators, mongoose that can overcome the bites of cobras, little grasshopper mice that battle scorpions and are unaffected by the sting … the list goes on and on."

While we do not yet know the precise mechanism by which the alligator lizards resist the black widow's venom, other predator-prey interactions can give us an idea as to what biochemical mechanisms might be at play.

"Other animals that resist venoms often have 'toxin scavenging' proteins in their blood that bind to venom and disable the toxins," Feldman said. "Because the alligator lizard showed no muscle tissue damage at all, or even an elevated immune response, we suspect that the venom is hindered or bound up even before it can do its dirty work.

"In terms of how this could have evolved, these lizards eat all sorts of potentially harmful arthropod prey, from stinging ants and wasps, to various kinds of spiders, and even scorpions. Perhaps all lizards have some ability to withstand the venomous jabs of arthropod prey, and evolution simply tweaked those ancient tools to allow these lizards to deal with widow spiders.

"It's really exciting to think that these lizards may actually be engaged in a predator-prey arms-race with dangerous spider prey … Some spiders and lizards may be involved in co-evolutionary struggles right under our noses."

Further research into the mechanisms by which the lizards resist the venom could have significant implications for human medicine. "While black widow bites are not usually dangerous, they are very painful and can cause illness, requiring medical attention," Feldman said.

"If we can figure out what molecular or biochemical tricks these lizards are using, then we might be able to create medicines or therapies to rapidly and effectively treat spider bites."