Bird-dropping Spider

29 August, 2011

Bird-dropping Spider with five distinct egg sacs <i>Celaemia excavata </i>
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.

Comments (11)

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valerie scarr 22 September, 2014 09:56
We are so fortunate to have two of these spiders with egg sacs,one in the front garden,one in the back ,we are concerned,as one of the spiders seems to have disappeared,she was a good Mum,always sitting on her eggs.
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Dee Harris 15 June, 2013 19:27
Hi there I was quite excited to find your site. I have been watching my bunch of eggs for several weeks. No spider tho.. The nest around the eggs has been damaged and torn apart. So I have bought them inside in a box . I didn't want to lose them as it has been over 20 yrs since I found my last one.. My worry for the little ones who have just hatched three days ago is what do they eat and at what time can I put them out in this cold weather..I thought maybe a safer place might be in a climber, mandavillia or in a citrus which doesn't lose leaves. I had a mother one and eggs when I was in about 3rd grade I love them others think I am nutty. I just want to see them survive and want others to see this little lady and babies. So how can I help them survive....? Look forward to learn how I can help my little babies..
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Discovery Centre 7 July, 2013 09:56

Hi Dee, apologies for the delay in getting back to you. Bird-dropping Spiders are common in suburban backyards but their remarkable camouflage means they are not often seen. The spiderlings hatch in late winter and they develop through spring, maturing in summer. The adults combine their amazing camouflage with an amazing strategy for capturing prey. Females produce a pheromone which mimics that of female moths belonging to a particular family (Noctuidae) and use this to deceptively attract male moths to their deaths. The young spiders, however, feed on a range of small insects.

At this time of year there are few small insects available, and they wouldn't normally hatch for some time. Perhaps bringing them inside has warmed them up and caused them to hatch prematurely. They are difficult to feed at this stage of development, so the best option may be to put them back outside and allow them to fend for themselves. Because they are generalist predators, it doesn't matter where you locate them - they will move around by themselves to find the best locations. Like all spiders, they are cannibalistic when very young and get by through eating unhatched eggs and other spiderlings.

The other notable characteristic of this species is the high rate of parasitism. Tiny black wasps lay their own eggs inside the egg sacs of Bird-dropping Spiders, and the wasps of the following generation drill small holes through the egg sac to free themselves. Parasitism is so high that it's rare to find egg sacs without these small holes in them, although the wasps never consume all the eggs in any particular egg sac.

Good luck and it's refreshing to see your ongoing interest in this species. 

Discovery Centre 4 May, 2012 14:19
Hi April, it may be that there are similar species from this genus of spider that occur in California. The best thing for you would be to contact one of the Natural History Museums in California, see this link, who will have a better idea of the spider fauna there than we will. The Bird-dropping Spiders tend to rely on their camouflage to protect themselves and would certainly not go out of their way to attempt to bite animals that are not their prey.
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April 4 May, 2012 10:21
I read Bird-dropping Spiders live in Australia. I believe we have this spider in our backyard, but we live in California. Do they live in the United States? We have ten eggs sacs hanging off our patio cover. Will these spiders bite our dogs if they go outside at night? We've never seen a shelled spider, ever, so we are a bit concerned.
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Matt 10 April, 2012 20:03
I have a bird droping spider in my backyard it has been there for a few months, it has 5 eggs and one of the eggs has a little hole in it. Does that mean that the little ones are coming out?
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Discovery Centre 8 March, 2012 17:07
Hi Jackie, the Bird-dropping Spider feeds on moths, (as you have observed), so she wouldn't attack the Harlequin Bugs as a potential meal. The survival of the female spider is based on her camouflage, if she moves during the day a sharp eyed bird is likely to pick her off for a meal. So I am assuming she has not considered the Harlequin Bugs near her eggs to be enough of a threat for her to risk moving. 
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jackie airs 8 March, 2012 16:22
I have been watching a bird dropping spider and have observed something i think is unusual and hope you can explain what was going on. saw my spider hanging about 2 inches from her 4 egg sacks and 2 harlequin bugs roaming in what appeared to be in an excited manner over the eggs.with a small twig i poked and tried to move them but they seemed to be reluctant to go. after getting rid of the bugs i nudged my spider and she was ok she returned to her eggs at night laid another egg sac and caught 2 moths.Harlequin bugs eat plants so i'm confused as to why she didn't attack them she is always guarding her eggs.
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Discovery Centre 16 December, 2011 13:05

Hi Chelsea - we do offer an identification service, but obviously we can't provide an identification on the basis of your description, we would need a clear photograph. The guidelines for using our free identification service can be found here

Hope this helps

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chelsea 16 December, 2011 12:31
i found a spider that has a yellow bum and 2 little white spikes and it is a little fluffy what is it?
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Louie 1 September, 2011 20:27
I have been watching a bird dropping spider with her egg sacks for a few months now. Today i felt very fortunate to see some of her babies. Very cute little creatures.
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