Piotr Naskrecki was out for a nighttime walk in a rainforest in Guyana, when he heard something creeping underfoot. He expected to find a small mammal like a possum or rat. What he found was unlike anything he had ever seen before.
"When I turned on the light, I couldn't quite understand what I was seeing," said Naskrecki, an entomologist and photographer at Harvard University's Museum of Comparative Zoology, according to LiveScience.
A second later, he realized what he was looking at wasn't a furry mammal, but a gigantic, puppy-sized spider.
Known as the South American Goliath birdeater (Theraphosa blondi), the huge spider is the world's largest arachnid, according to Guinness World Records. The spiders legs can reach up to a foot or around the size of "a child's forearm," with a body the size of "a large fist," Naskrecki said to Live Science.
The spider can weight close to 6 oz. (170 grams), about as much as a young puppy, Naskrecki wrote on his blog. Some people say the giant huntsman spider, which has bigger legs, is larger than the birdeater. The huntsman is more delicate than the birdeater however, and comparing to two would be "like comparing a giraffe to an elephant," Naskrecki said.
When Naskrecki approached the creature in the rainforest, it would rub its hind legs together against its abdomen. At first, the researcher said the spider's behavior was "cute" but then he realized it was sending out a cloud of hairs with microscopic barbs on them.
When these hairs get in the eyes of other mucous membranes, they are very "painful an itchy" and can stay there for days, he said. The hairs aren't the spider's only line of defense however.
The birdeater also sports a pair of 2-inch-long fangs. Though the spider's bite is venomous, it's not deadly to humans. It would still be painful, Naskrecki said, comparing the pain to driving a nail through your hand.
Despite its name, the birdeater doesn't usually eat birds, though it is capable of killing small mammals. "They will essentially attack anything that they encounter," Naskrecki said.
The spider mainly hunts at night, so the chances of it encountering a bird are very small.
Birdeaters are also not a very common spider to find in the rainforest. Naskrecki was able to take the female birdeater that he found during his walk back to his lab to study. She's since been deposited in a museum.
"I've been working in the tropics in South America for many, many years, and in the last 10 to 15 years, I only ran across the spider three times," Naskrecki said.
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