This is the extraordinary Bird-dropping spider Celaenia excavata. There are no prizes for guessing where it gets it name. Masquerading as bird dropping seems like a great way to dissuade a bird, or other predator, from eating you.
The spiders in the photos are females which have a body length of around 12mm. The males are not often seen as they are quite tiny at about 2.5mm in length. By the way, another common name for this species is the Death's Head Spider as from certain angles it has the appearance of a skull.
What's So Extraordinary About It?
First up is has an extraordinary diet. It feeds almost exclusively on moths and not just any moths, but only male moths. As Julius Sumner Miller may have asked, "Why is it so?" The reason is that this spider emits pheromones that mimic those of many female moths. Males moths are thus attracted and come in close looking for a female. But wait, there's more! Although a member of the Araneidae family (Orb-weaver spiders) she does not catch the moths in a web. Rather she dangles a thread of silk with a glob of sticky liquid on the end. When a moth approaches she swings it, the globule sticks to the moth, and she reels him in. Extraordinary indeed! (See illustration further down) For this reason, the subfamily to which these spiders belong, Mastophorinae, are sometimes called Bolas spiders.
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Bird-dropping Spider - Celaenia excavata
Bird-dropping Spider with a more alert stance.
They stand out well in the photos but when you are looking for them they are quite well camouflaged
As seen in this next photo, from above it can look a bit like a skull. This is where it get's it's alternative name of Deaths Head Spider.
From above they look like a skull
Below is an illustration of the Bird-dropping spider swinging it's bolas .
Hunting technique - Swinging the bolas. (Illustration by my daughter)
A Useful Biological Control Agent
Yet another common name for this moth is the Orchard Moth as it is often found on fruit trees. Indeed the spiders above were found among my apple trees in the backyard. Here in Tasmania, one of the worst pests of Apples, aside from possums, is the Apple Codling Moth, Cydia pomonella. The larvae of these moths are the so called 'worms' that you might find in your apple (or worse still, the half worm you find in your apple). So having the Bird-dropping spider in your apple tree is going to help to control the moth population. Of course you can always spray your trees with insecticide but in doing so you are also going to kill of the moths natural predators.
The Codling Moth, Cydia pomonella, at my backyard light trap. For information on Light Traps see the post at this link
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