Theridiidae: Cobweb weavers

A large spider family, including some very famous world spiders such as the North American black widows (Latrodectus sp.), the Happyface spider (Theridion grallator) and the social spider (Anelosimus sp.). The 56 British species are small to medium spiders. They make irregular webs of criss-crossed threads with some of them stretched and loaded on one end with sticky dropplets, which break when an insect struggles to break free and lift the prey in the air like snares. The genus Episinus, however, produce the most remarkably simplified web, a 'H' shaped with four sticky threads connecting the spider to the ground and an over head support. Theridids have a relatively large, well marked abdomen with a diversity of patterns and colours.  This family includes one of the most fascinating examples of maternal care in spiders.

Powerful hunters
These spiders are able to throw sticky threads over prey to immobilise them. This ability, and their rapidly acting venom, makes them formidable hunters able to subdue much larger prey.

Steatoda bipunctata with immobilised Ectemnius wasp

Even the powerful and agressive male Anthidium manicatum couldn't escape Enoplognatha sp.

A wasp? No problem for Enoplognatha

Not even a honeybee. Note the typical web of Enoplognatha, tangled around a flower, ready to catch visiting insects, with the spider neatly hidden under the flower itself.

Enoplognatha doesn't even care about the chemical secretions of shieldbugs.

Colour polymorphism
Enoplognata  comes in several colour morphs. There is a white morph and one with a pink stripe. This is the pretty and rarer pink morph.

Stridulating males
Steatoda bipunctata males have a serration at the end of the cephalothorax which rubs against teeth at the front of the abdomen making an just audible stridulation which is used during courtship. In his field guide to the Spiders of Britain and Norther Europe, Michael Roberts writes:

I first heard this in use as a medical student. Quietly studying the anatomy of the brachial plexus, I became aware of a quiet sound from a guitar standing in the corner. My initial thought was that one of the well worn strings was very slightly creaking as if about to snap and I  clearly remember tensing myself for this not uncommon event. It turned out to be a pair of Steatoda bipunctata mating inside!

This is the male of Steatoda bipunctata. It waves it's large palps as it runs on the ground looking very ant-like. The female (top shot) has a look reminiscent of a fat tick, its cephalothorax almost hidden by her large, shiny abdomen.

Maternal care
Theridids make egg sacs that are attached to their web, or under a curled leaf retreat, and are often guarded by the females. Some species even carry the egg sacs attached to the spinners. The presence of females protects the eggs from predation, for example from ants. The mother will react to the presence of ants by relocating the egg sac more centrally on the web. Enopognatha guards her egg sac under a curled leaf and stays with the spiderlings until her death.
The small Theridion sisymphium female produces a bluish egg sac, which she guards. When the spiderlings emerge she will feed them  mouth to mouth with regurgitated food. Later, she will share prey with them until they are ready to disperse.

The wonderfully weird egg sac of Theridion pallens

The blue egg sac of Enoplognata sp.

The tiny Theridium pictum with her egg sac (note the screw head for scale). This species lives near other spiders webs and steals food from them. 

Enoplognatha with her brood inside a curled leaf.

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.

Summery wildlife garden

A walk around the lush meadows of the wildlife garden yielded a number of invertebrate sightings. The day flying Six Spot Burnet moths, with their bright red-pink and dark metallic wings feasted on the knapweed (above).

A Meadow Brown feeds on the abundant oregano.

I caught a Small Skipper and a Six spot burnet on knapweed.

These are two shots of Small Skippers, one of my favourite butterflies. The way they carry their wings, held at different angles, instead of pressed together like other butterflies, is quite characteristic.

On the grass, there were many nursery webs of the nursery web spider Pisaura mirabilis. With a bit of patience, the guarding females could be spotted on or under the tents. She guards the eggs, and then the spiderlings which hatch inside the nursery web and remain in it for a few days.

A female Pisaura mirabilis.

My first summer generation Comma Butterfly.

And the first Gatekeepers. These two weren't wasting any time and were mating

Male Gatekeeper.

A Ringlet sat atop a ragwort inflorescence. Once I got closer, I realised the butterfly was dead, prey for a spider that often builds its web under flowers, Enophlognatha ovata.

This large hoverfly is one of my favourites, Chrysotoxum festivum. I often see a male hovering over the pond in the wildlife garden.

I took this shot on the 9th of July this year of the hovering male.

And in the oregano, a cuckoo bumblebee, Bombus ruderarius rupestris which parasitizes the similar looking Bombus lapidarius.

Candy-stripe spider

 I found four Candy-stripe spider, Enoplognatha ovata, females guarding their lovely blue egg sacs under the lid of my garden waste bin. The spiders have probably been transferred to the bin with branches cut from some bushes, and had moved with their egg sacs to the drier lid. This one floated down from a thread of silk, and I brought it home to take her portrait on the white bowl. Another thread of silk attached the female to its egg sac, as can be seen on the following side shot:

Although these are small spiders, about half a cm long excluding the legs, they are powerful hunters, and they are able to subdue wasps, honeybees and even the aggressive Wool Carder bees, which they capture on their loose, disorganised web under flowers or leaves, where the females guard their egg sac:

Enoplognatha with its male Wool Carder Bee prey

this one with wasp

with Episyrphus balteatus hoverfly

This one hiding underneath a Feverfew flower got a honeybee

This spider shows a striking color polymorphism, which is genetically determined in a complex way. I have found the three colour forms in my garden. The abdomen can be plain pale yellow (variety lineata, top shot), yellow with two dorsolateral pink stripes (var. redimita):

or yellow with the dorsal surface of the abdomen entirely pink (var. ovata), the rarest in my garden:

In addition to the colour polymorphism the presence and number of black spots is also variable, as it can bee seen in the above photos. This species also occur on both coasts of the USA, presumably introduced from Europe. In the UK, there is a very similar species, also colour polymorphic, E. latimana, which has been recorded mostly in the south of England and it appears to be less common than E. ovata.