Mimetidae: Pirate spiders

This is a small, but fascinating spider family. It comprises just 4 species of the genus Ero, two of them common and widespread.  They are small spiders, about 5 mm long, with globular abdomens, which have two or four tubercles. They have annulated legs, the first pair endowed with a series of spines.

Spider eaters
The Mimetidae are specialists in eating web-building spiders. Ero does not build a proper hunting web, it is a nomadic species which wanders in search of webs. Once found, she may invade the web, and then pluck it with her front legs. The owner might come to investigate, as it would do if an insect had fallen in, but then Ero will quickly grab and bite one of the spiders legs. The venom is quickly acting and then Ero will feed on the spider. In occasions the web owner might be able to escape minus a leg

Stalked egg sacs
Female pirate spiders produce characteristic egg sacs, which are more noticeable than the spiders themselves. They have a long stalk and are covered on coarse, brown wavy silk, presumable for protection, as the female takes no care of the egg sac or the spiderlings themselves.

These two photos are the only ones I have possibly portraying a Ero cambridgei/furcaca female sitting on a flower in a bush, legs withdrawn.

Cucumber spider with egg sac

 While looking for lily beetles, I found this female Araniella sp guarding its egg sac. The sac, made of coarse yellow silk threads, was attached to the underside of a leaf, and the female sat on a loose web underneath, where she was also eating an aphid (below). There are two extremely similar species, Araniella cucurbitina and A. opistographa, which can only be identified by inspection of their epigyne. Both are small and bright green, with a red mark over their spinnerets, which can often be seen from underneath. They live in trees and bushes, and are orb weavers, although their webs are quite small.

Pholcus before and after laying eggs

The first female Pholcus phalangioides laid eggs at the top of the porch last week. The gravid female I was following, which lives under a shelf in the outside toilet was still without eggs yesterday. This morning when I checked, she had laid. Check her abdomen before (below) and after laying (top).

Garden Centre Spider (II)

Another visit to the garden centre. I spend much of it looking up most, in search for the Garden Centre Spider, Uloborus plumipes. I must have been a funny sight. My efforts are rewarded quickly. First, and most obvious I spot the webs, stretched across the plumbing by the glasshouse roof. They are laid almost horizontally and is an orb web. This one had a stabilimentum, a decoration in the centre of the web, in this case a linear one.

The spiders were a bit harder to find. After a while I saw some piece of debris hanging from some web, see the spot in the middle of the photo?

Zooming in, it revealed itself a a superbly camouflaged spider. It is hard to think it is a spider from a distance. Once I had spotted one, more followed, and I counted five in a relatively small area. 

The nicer thing, though, was to find its spiky egg sac too.

Sorry for the poor photo quality, but the spiders were 3 m above me and the light already fading.

Motherly candy-striped spiders

I find maternal behaviour of spiders fascinating, and I keep an eye for it whenever the opportunity arises. When repotting my gingko bonsai on the 2nd of September, I noticed a couple of rolled leaves. They contained web shelters of Candy Striped Spiders Enoplognatha ovata/latimana. One of them had a female with her egg sac, the other already contained spiderlings (above). I checked today again, both females were guarding their spiderlings. The first one approached the entrance of her leaf to check what was causing the disturbance, the spiderlings clustering together like Araneus spiderling balls. The spiderlings have been in one of the nests for almost two weeks. Will the presence of their mother increase their chances of survival? will the mother feed during this time? In the related genus Theridion (Enoplognatha ovata was previoulsy called Theridion ovatum) the presence of the mother guarding the egg sac appears necessary for egg survival (although there were some loses due to parasitism from a tiny wasp). The mother not only sits near the egg sac, attached to her by a silk thread, but she is on the alert, and will move the egg sac to the centre of the web when predators are nearby. Unguarded egg sacs are rapidly predated by insects (ants, earwigs) and other spiders. And what about the spiderlings? what do they have to gain from their mother's care? In the Happy Face Spider, Theridion grallator, the female loosens the egg sac allowing the emergence of the spiderlings, and then captures prey for her brood. The spiderlings are under the female care up to three months, until they disperse and feed on their own. The female might produce another egg sac if the first one is lost, but she will die by the end of September early October. The spiderlings will disperse and overwinter near the ground.

One of the females, in close contact with her egg sac (2/9/14)

More information

British Arachnological Society.

Spider eggs and egg sacs

Spiders make remarkable mothers. One of the most widespread maternal behaviours is the more or less elaborate construction of an egg sac, and many species are making them at this time of the year. The mother wraps a batch of eggs - which might be the only one she will produce during her lifetime - into a neat parcel kept together with silk. The egg sac can protect the eggs from parasitic wasps, or from predation - sometimes from other spiders. In addition, egg sacs are often guarded by the mother, like the Neriene montana above (28/05/2014) or Garden spiders (below), Araneus diadematus, which guard their large egg sacs until they die at the end of autumn (30/10/2011).

Holding the egg sac is another maternal behaviour. An example is Pholcus phalangioides, the splindly daddy long-leg spider. She makes a simple egg sac, with the eggs clearly visible through the lax packaging. She keeps the eggs on her mouthparts until the spiderlings hatch (22/07/2009).

Being mobile spiders, wolf spiders and nursery web spiders actually carry their egg sac with them wherever they go. This allows the eggs to develop faster, as they warm up when spiders bask in the sun.

Wolf spider, Pardosa sp. carrying her egg sac (31/05/2011), attached to her abdomen.

Nursery web spider carrying its large egg sac (19/06/2011).

In the family Gnaphosidae, the female not only guards the eggs, but she makes her egg sac inside a folded up leaf, locking herself inside with the eggs (19/07/2010):

But egg sacs are often found alone. Some of them have a stalk, like those of the genus Ero, also distinctive by their covering of coarse red silk (7/04/2013):

Others are truly unique, and is the best way to identify the species, like the sputnik-like egg sac of Paidiscura pallens, a tiny spider (28/05/2014).

Eggs vary in colour, I love the soft pink eggs of Steatoda bipunctata (28/05/2014)...

 ...and also the baby blue silk of Enoplognatha sp., revealed here while picking apples (30/08/2011):

These are just a few examples, from common spiders you can find in your own garden, which illustrate some of the diversity of spiders.