A photographer and entomologist from Harvard University's Museum of Comparative Zoology on a nighttime stroll in a rainforest in Guyana found he had some creeping company -- nothing less than the world's largest spider.

Piotr Naskrecki said he heard a rustling sound from the forest's floor, and turning on his flashlight found himself sharing his nighttime walk with a South American Goliath birdeater, a spider whose legs can span a full foot, attached to a body Naskrecki described as the size of "large fist."

They can weigh as much as 6 ounces, as heavy as a small puppy, he says.

No silent stalker, the feet of Theraphosa blondi "have hardened tips and claws that produce a very distinct, clicking sound, not unlike that of a horse's hooves hitting the ground," he wrote on his blog.

Because of its size, the Goliath is likely to be the only spider in the world that can be heard as it walks, he said.

Despite its name, he explains, birds are not a normal meal for the birdeater, which prefers whatever it can find on the forest floor, including insects, earthworms and frogs.

Still, if it found a fallen nest on the forest floor it could kill any birds found in it, and it's capable of killing a small mammal, injecting a venom through fangs that can reach 2 inches long.

"They will essentially attack anything that they encounter," Naskrecki said.

When surprised or threatened, the spiders can emit a loud hissing noise, using hairs covered with microscopic hooks on their long legs that they rub together to create the sound.

Goliath birdeaters are members of the tarantula family, Theraphosidae.

Their common though likely inaccurate name has been applied ever since an 18th century engraving depicted one of them eating a hummingbird.

Females can live for 15 to 25 years, but males die soon after they reach maturity and only live for around 3 to 6 years.

Oh, and females will sometimes eat their mates.

The giant spiders live in burrows, are nocturnal and are found in rainforests of Guyana, Surinam, southern Venezuela and northern Brazil.

However, they remain rare and are not often spotted, Naskrecki points out.

"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," he says.

Naskrecki said he took the example he discovered in Guyana, a female, to his laboratory to study it.

It now resides in a museum, he said.

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