Strolling through a Guyana rainforest one night, a scientist heard some rustling and thought he'd encountered a furry mammal. Well, he was right about the furry part. The creature was actually a Goliath birdeater spider, LiveScience reports—the world's biggest type of spider, according to the Guinness Book of World Records. It can weigh up to 6 ounces. For comparison, National Geographic reports a black widow weighs roughly .035 ounces; that's 170 times lighter. Scientist Piotr Naskrecki writes its weight is "about as much as a young puppy," while its leg span can be a foot long, comparable with a kid's forearm, notes LiveScience. The body itself is fist-sized, Naskrecki says. The fangs? Two inches long. The thing won't kill you, but its bite feels "like driving a nail through your hand."
And when it rubs its legs on its body, it can fire out hairs carrying tiny barbs, which can really hurt and itch if they get you in the eyes. Ultimately, however, it seems the spider is just unpleasant, and not too common: "A chicken can probably do more damage," Naskrecki notes, adding that he's only seen one three times in as many as 15 years spent working in South America. Though MNN reports the spider was given the "birdeater" name after being discovered while eating a hummingbird, "they rarely have a chance to [kill birds] while scouring the forest floor at night," Naskrecki writes on his blog. "Rather, they seem to be feeding on what is available in this moist and warm habitat, and what is available is earthworms—lots of them." (A possibly freakier spider story: A spider burrowed into a man's chest for three days.)