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 (23)

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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.
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?
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

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.
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. 
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?
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.
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.
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..
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. 

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.
Michelle 18 December, 2014 13:59
I've just come across your site looking for what type of spiders I have in my garden laying brown spikey eggs. fascinating to watch. One keeps laying an egg, she has 3 & looks like another is on the way. I was also amazed to find another when I pulled down an old outdoor blind, she was wrapped up in with 10 eggs! I put her in a dry protected place safely with all her eggs, & looks like she has another on the way. Insects are amazing! I encourage them in my garden with companion plants amongst the veggies. Thanks for the info.
Julie Aylwin 19 January, 2015 11:47
I have this amazing Bird-dropping Spider in our garden. I discovered her about twelve months ago. I watch her in the mornings from my kitchen window as she delights in sucking from her moths usually two that she has caught during the night.She has created 10 sacks and has neatly spun her web to secure them.On Sunday I counted 6 little babies then by evening there were about 15 the next morning when I checked I could only find one baby. Do the Bird-dropping Spiders re-produce with partners?. Does she kill her mate after mating as I found on a higher branch the skeleton of an adult Bird-dropping Spider. I really enjoy watching her grow and to witness antics. I live in Victoria. Thank-you.
Discovery Centre 4 February, 2015 09:24
Hi Julie, Bird-dropping spiders do reproduce sexually; the male is much smaller than the female, less than a quarter of her size. There doesn't seem to be much information suggesting that the female eats the male. 
Jen 16 October, 2015 11:55
Do these spiders hunt by using a web to catch moths or do they wander close to their nest to pounce on moths?
Discovery Centre 17 October, 2015 12:02
Hi Jen,

These spiders only use webs to suspend their egg sacs. Instead, Bird Dropping Spiders feed on male moths, which it attracts by releasing pheremones that mimic female moths. When the moths fly close enough, the spider grabs them with its forelegs.
Jenny 23 February, 2016 22:17
Over the last few weeks, I have discovered a Bird Dropping Spider in my front yard. She is amazing and so totally clever to have created her egg sacks the way she has. I have photographing Mum and her eggs over many days and have been sharing these with my Grade 5/6 class. My students are as equally fascinated as I am. We have been searching to try to find out how old our Mrs Spider might be and what her life span could be? How long before we may see spiderlings??? I noticed the egg sacks two weeks ago as they are just near my mailbox on my front lawn. Unfortunately I have a terrible feeling that, as of today, Mrs Spider may be dead. I've checked her twice in the last couple of hours and she is hanging from a single strand of web in a very perculiar manner. She is also looking very dry. Can the eggs sacks survive without her? Thank you.
Discovery Centre 3 March, 2016 16:43
Hi Jenny, 

Bird-dropping Spiders (Celaenia excavata) females can produce 12 or more egg sacs, and remain with them until they hatch. The spider is cryptic and immobile at the best of times, so often it’s difficult to tell if it’s dead, but it definitely sounds as if yours is. The eggs are parasitised by tiny wasps that lay their own eggs into the spider’s egg sac, and the wasp larvae consume the spider eggs. There is a very high rate of parasitism and the female spider does her best to protect the egg sacs from parasitic wasps, but she doesn’t seem to be able to make a great deal of difference. When ready, the spiderlings will hatch from the egg sacs as normal, whether she is present or not. This species is interesting in that adult females produce a special pheromone (sex scent) that attracts not other spiders mimics the pheromone produced by female Owlet Moths. Male Owlet Moths, mistaking the scent for a female moth, fly to the spider and are quickly captured and consumed. Although classified as orbweavers, Bird-dropping Spiders don’t build prey-catching webs due to their unusual technique for catching moths.

Libby lewis 15 April, 2016 01:01
Hi, from what I've read, bird dropping spiders live on the east coast and southern Australia. I live in Geraldton, a coastal town of Western Australia situated 4.5 hrs north of Perth. I have a bird dropping spider making a few sacs under a leaf of my frangipani tree. I'm glad to read that their harmless to humans - it is very fascinating to see such an exotic looking species. Is it rare to see them this far north, on the west coast?
Discovery Centre 15 April, 2016 11:48
Hi Libby! From looking around online, it would seem there are sightings in WA, but you might want to grab a picture and run it past the enquiries folk at the WA Museum to confirm!
Mary 17 August, 2016 16:55
We are so excited today to finally watch the baby spiderlings emerge from their sac and float away on the breeze. The mother has moved twice and now (late afternoon) she is sitting at the hole perhaps warning the spiderlings to stay inside? as none have emerged for a while - yet every few minutes we can see some activity at the hole, so the sac is not empty yet. Absolutely fascinating, and the tiny stripey spiderlings are very cute.
Discovery Centre 18 August, 2016 11:20
How lovely Mary, thanks for sharing!
Brett Lazdins 14 April, 2017 20:16
Hello. This is the 2nd female with eggs we've had in the yard. The first was many years ago, a Hobart-area house...larger spider, only 3 large eggs, none viable. Seven of this females' 15 eggs have hatched. She's hunting now, she's hanging with her front sets of legs hanging in a catching pose. Does she drink the moth? Usually in the morning she has one rolled-up like an impromptu straw. After a few days of egg. Small eggs, but a lot of them. Tiny offspring, waiting for the right breeze. Streamers of silky threads left behind on the camellia bush. Very cool.
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