A scientist enjoying a moonlit walk through a South American forest has received the fright of his life after stumbling upon the world’s largest spider.

American entomologist Piotr Naskrecki wrote about the experience in a blog post called ‘The sound of little hooves in the night’, detailing how he heard the rustle of an animal running and thought it was a rat.

“I could clearly hear its hard feet hitting the ground and dry leaves crumbling under its weight,” Mr Naskrecki said about being confronted by the Goliath birdeater spider.

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The spider is the largest in the world and can weigh more than 170 grams or “as much as a small puppy”, according to the Harvard-based scientist.

The leg span of the creature is 30 centimetres long and its fangs are “capable of puncturing a mouse’s skull”.

Although they are capable of killing small birds and are called birdeaters, Mr Naskrecki said the spider lived mostly off earthworms.

When feeling threatened, the spider protects itself by rubbing its rear legs together to make a noisy hissing sound.

It also releases sharp hair from its abdomen which irritates the eyes and nasal passages of its predators.

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“First, the spider would start rubbing its hind legs against the hairy abdomen,” Mr Naskrecki wrote.

“‘Oh, how cute!’, I thought when I first saw this adorable behavior, until a cloud of urticating hair hit my eyeballs, and made me itch and cry for several days.”

Luckily the Goliath birdeater’s poison is not venomous to humans, but many would disagree with the insect expert when he calls the giant spiders ‘cute’.