Zoologger is our weekly column highlighting extraordinary animals – and occasionally other organisms – from around the world

When Phrynarachne decipiens curls up it looks like bird faeces (Image: Joseph K H Koh)

Species: The bird-dung crab spider (Genus Phrynarachne)

Habitat: Undergrowth at forest fringes in South-East Asia

This spider has gone to town in making itself look like crap – literally.

Bird-dung crab spiders spend a lot of time sitting motionlessly on the leaves of plants waiting to attract insects such as flies for dinner.


Most other creatures out in the open would be like sitting ducks. But these spiders have a trick up their sleeves – they mimic bird droppings in colour, shape, size and smell, deceiving predators. When they draw their legs close to their body and stop moving, the masquerade is complete.

“Birds, almost all with good eyesight, will not go for what appears to be their own turd for food,” says Joseph K.H. Koh of the Lee Kong Chian Natural History Museum in Singapore.

The spider’s body has a glossy surface that gives it a “wet” look of fresh faeces, says Koh. “The nodules on the body and rough-edges of the legs further reinforce the ‘shitty’ look – pardon the rudeness,” he says.

When the spider moves, the illusion disintegrates. “The ‘walking poop’ no longer looks like a piece of dropping, especially with its legs spread out,” Koh says.

The illusion breaks when it moves (Image: Joseph K H Koh)

As if all this isn’t enough, occasionally it will add another touch, sitting on a thin patch of its own white silk to simulate a dried-up splash of bird droppings.

Bird-dung crab spiders aren’t the only masters of faeces disguise among arachnids. Others include species of orb weaver, especially those from the genus Celaenia, says spider expert Robert Whyte.

And mimicking bird droppings isn’t exclusive to spiders. Black-and-yellow Asian swallowtail butterfly caterpillars (Papilio xuthus), for example, are black and white with spines and look similar to bird droppings.

But what marks the bird-dung crab spider out is its smell.

Foul smell

Long Yu of Hubei University in China and his team have shown that the spider Phrynarachne ceylonica‘s foul smell may help it attract prey and deter predators.

The team exposed the spider to one of its predators – jumping spiders – and houseflies as prey. This showed that the camouflage helps them repel more jumping spiders and attract more flies than the controls without the camouflage.

They presented their findings at the Behaviour 2015 meeting in Cairns, Australia, last month.

“This is the first illustration that the spiders could also use the chemical cues to try to decrease the predation rate and also increase the attraction of prey,” says I-Min Tso of Tunghai University in Taiwan, who wasn’t involved in the study.

The ability to produce smells is rare among arachnids, but not unique to bird-dung crab spiders. Bolas spiders, for example, emit chemicals that imitate the smell produced by female moths to attract male moths. Confused males are drawn by the smell, only to be captured and devoured by a hungry spider.