Tuesday, April 22, 2008

Bird-dropping Spider, Celaenia excavata

How do these spiders that have no web and hardly ever move, catch their prey?

Unlike the fast moving spider in my previous thread, this spider is quite the reverse, seldom moving at all. It is camouflaged as a bird dropping during the day to be overlooked by predators that might be tempted to eat it. However at night it will hang up side down in an exposed position with its front legs outstretched, just waiting for something to fly into them.

The Bird-dropping Spider Celaenia excavata

Now spiders with large webs often have trouble catching insects that refuse to fly into them, so how does this spider get something to literally fly into its arms? Well this bird-dropping spider does do it, and not just any insect, but a moth of a specific gender and often a particular species! It is hunting a male moth that is attracted to the pheromones the spider releases that mimic those of a female moth ready to mate. So the male moth thinking he has located a nice receptive lady, ends up in the spiders deadly grasp.

A hunting Bird-dropping Spider

The deception of this spider however does not end there, for there is another that will guarantee success and its evening meal. The male moths do not fly directly to the female, but will initially circle around her to make sure of her presence, for this purpose he has reasonably good eyesight. Now on the photo below squint your eyes and imagine it is nighttime with a shinning moon, and what do you see? A moth, with the white parts of the spider's front legs and abdomen appearing like wings and the central portion of the spider's abdomen, the moth's body; resulting in the moth willingly flying into her waiting arms.

Squint your eyes to see the moth

Although this bird-dropping spider may not look much, it has evolved three highly sophisticated means of not only deceiving predators but successfully attracting prey.

This specific Bird-dropping Spider, Celaenia excavata, is one of the larger bird-dropping spiders with the females growing to around 15 mm (excluding legs), but like their predators, people too seldom notice them, although they may spot her egg sacs. These are spherical and almost as large as the spider herself, which she attaches to strong silken threads. The male spider is only a quarter the size of the female and is seldom, if ever seen.

Looking after her egg-sacs

Bird-dropping Spider, Celaenia excavata

Celaenia excavata is a widespread Australian (more common in Eastern States) and New Zealand species, but has taken to citrus and fruit orchards as a preferred habitat. It is often so common in this man-made environment that it is also known as the Orchard Spider.

The rear end

If you are fortunate to encounter one of these spiders, take a minute to consider how sophisticated they are, as a master of deception they have few equals, being exceptionally well adapted to the niche they have carved for themselves.


Junior Lepid said...

Thank you for this great article on the Bird-dropping spider.

Celaenia excavata is allegedly common in Victoria - but I am yet to find one in my area - and I have been searching!

Perhaps later, when we enter the summer period again, I will go on night patrol in some remnant vegetation nearby and, hopefully, have better luck.

Esperance Blog said...

Hi Junior Lepid,
You have chosen a very difficult spider to find, but as said in the blog, if you can find the egg-sacs, the spider is usually not far away. During spring would be a good time to look, as the one I was watching has now disappeared.

I don't think looking at night will give you any advantage as it is still the egg-sacs that are the most obvious. However you might find a lot of other things.

Keep in touch,

Tsun-Thai Chai said...


What a beautiful spider you have photographed! The word "breathtaking" came to mind. It's simply mesmerizing.

Cheers, Chai

WA said...

Thanks Chai
The Banded Orb Spider might also interest you.

Anonymous said...

I have been searching the web intensly for this spider!
I am from Mandurah WA and discovered one on my washing line. it resembled a tiny frog curled up and seemed to have a hard shell. and i had no idea what on earth it was. it had me baffled! what a curious little spider!

Ned said...

What a beautiful and intriguing spider. I first saw this spider egg on a palm leaf at Tafe. Then I found one in my Mum's garden and on the rubbish bin.

Have now been watching with interest and many photos later.

Over a period of time I noticed that the one had become two and then it became three.
I was rubbing the egg with my finger and I saw something move, well a little shudder came over me as that was the one I was rubbing.LOL.

I had looked under the leaves and through the shrub but did not see anything. Now I understand why I did not.

Be curious to see next season whether she comes back to the same location