The Black-footed yellow sac spider’s appearance can fluctuate moderately by species. According to WebMD, “This spider only grows to the size of a nickel, but it delivers a painful bite that ...

There are close to 50,000 known species of spiders, with another 50,000 estimated to be undiscovered. While the creepy arachnids can be frightening to look at, many are harmless to humans.