Most animals that prey on insects, such as birds or lizards, stay away from the black widow spider due to the red marking on its back. Although eating the spider won't kill them, it will make them sick. They soon remember the red markings and remember to stay away from the black widow. A few animals, however, aren't bothered by the venom and frequently prey on the spiders.
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Black widow females are notorious for eating males after they mate. This reputation is largely undeserved as it rarely happens. Before mating is another matter. Males must carefully court the female before approaching to mate. This ritual can take up to 7 hours. If the females are unimpressed, the males must make a hasty retreat or wind up serving the females in an entirely different manner than they had planned.
One of the biggest enemies of the black widow are wasps, specifically the iridescent blue mud dauber (Chalybion californicum) and the spider wasp (Tastiotenia festiva). The iridescent blue mud dauber lines its nest primarily with black widow spiders and may kill dozens of them each year. The spider wasp also fees on the spider and uses it in its nest. Another wasp, the flightless scelionid wasp (Baeus latrodecti) preys on black widow egg sacs as do members of the chloropid fly (Pseudogaurax spp).
The black widow is more likely to prey on small lizards than become its prey. But at least one, the alligator lizard (Elgaria multicarinata), defies the odds and commonly feeds on the spider, The alligator lizard got its name because it looks like a small alligator. It's about a foot long, including its 6-inch tail, and light brown. It lives in the western United States in grassy or wooded areas.
Although the praying mantis is not as notorious for eating black widow spiders as wasps and alligator lizards, it has been observed doing so a number of times. The praying mantis is a large carnivorous insect that will eat anything it can get. Praying mantises will also eat small animals, including mice, frogs, lizards and hummingbirds. Praying mantises live across the United States and range in size from less than 1/2-inch to 12-inches long.