Daddy Long Legs
A relative of the daddy-long-legs has been discovered fossilised with a gigantic erection Scott Robinson/Flickr

A spider related to the daddy-long-legs has been found preserved in Burmese amber, with an erection nearly half the size of its body. The harvestman spider, Halitherses grimaldii, died around 99 million years ago, and is the first of its species to be discovered fossilised in amber with a fully erect penis – stretching nearly one millimetre.

The researchers, who published the "huge" discovery in the journal The Science of Nature, believe the spider was caught on the side of the tree when its body was encased by a jelly-like substance. This would eventually preserve its body for millions of years.

Spider penis
Researchers discovered the spider with a fully erect penis stretching nearly half of its body Dunlop et al.

The finding was discovered on a tree in – what is now – Myanmar. It has led to a new family of harvestman being confirmed, as the distinctive shape of its penis makes it stand out from its relatives.

The researchers describe the penis as: "A slender, distally flattened truncus, a spatulate heart-shaped glans and a short distal stylus, twisted at the tip."

Species – and even families – of harvestmen tend to look very similar. So much so that the only way to identify them sometimes, is by looking at their penises.

"Different families, and even species [of harvestmen], can have a characteristic penis shape," said Jason Dunlop, lead author of the study. He told National Geographic: "In fact, [penises] are often even more important than the shape of the body and legs."

Dunlop has does not know exactly why the spider died with a fully extended penis. He suggests that perhaps the spider's mate died beforehand, leaving it in a state of sexual arousal that ultimately lasted until he died.

"It might be the case that the animal was struggling as it was trapped in the tree resin," added Dunlop. "This caused the blood pressure to shoot up and the penis to become squeezed out accidentally."