Bird-dropping Spider with five distinct egg sacs Celaemia excavata
Image: Graham Milledge
Source: Museum Victoria
Question: A spider that looks like bird poo and whose eggs look like a bunch of grapes?
Answer: For the keen eyed amongst us, there is a fascinating surprise waiting in our gardens: the spider commonly known as the Bird-dropping Spider, Celaenia sp.
During the day, female Bird-dropping Spiders sit motionless with their legs drawn up against their body; this behaviour combined with their humped abdomen and black and white colouring makes them look just like bird poo.
This is a brilliant evolutionary strategy: no one wants to eat bird poo! Providing the spider doesn't move and give away its cover, it will not draw the attention of predators. The male, as is often the case with spider species, is much smaller than the female.
The hunting behaviour of this species is just as remarkable as its appearance: Bird-dropping Spiders releases a smell which resembles the sex pheromone that female moths use to attract males. When male moths fly in to investigate, ready to mate, they are grabbed by a Bird-dropping Spider.
Another interesting feature of this spider is its egg sacs. Bird-dropping Spiders can produce up to 13 egg cases. They are dark brown with black markings and, when suspended in the web, look like a bunch of dark grapes. The female keeps watch over the egg cases until the young emerge, usually in late winter to early spring.
While these spiders are rarely seen, they are likely to be quite common – their amazing camouflage ensures we don't often notice them. They're certainly a good species to have around, however, as they catch so many moths.