Araneidae: typical orb weavers

It's #arachtober, a whole month dedicated to the celebration of spider awesomeness and diversity! For this reason, I will be writing a daily post on the natural history of a British spider family.

For the first post, I have chosen Araneidae, the typical orb weavers. This is one of the largest spider families and include many familiar species, such as the garden spider (Araneus diadematus), the window frame spider, Zygiella X-notata, the wasp spider Argiope bruennichi, and the small cucumber spider Araniella sp. There are 33 species in the UK.  The drawing on the left shows the eye arrangement in the family (based on a photograph by Kiron Basu)

In foggy weather, orb webs become very visible, heavy with dew. The spider is sitting in the central hub.

A. diadematus spinning its web.

The spider's web
The most characteristic feature of araneids is that they spin flat, rounded webs with radial threads connected by a spiral net-like pattern of threads, which they attach to vegetation or other structures  The threads are sticky, and able to trap flying insects. The spider either sits in the middle of the web (often at night) or hides in a retreat on a corner of the web, with one of their legs touching a signal thread connected to the hub of the web, which allows them to detect the vibrations produced by any struggling insects. Orb spiders often eat their web at the end of the day, and build a new one in the morning. As they adopt a sit and wait strategy to catch prey it is easy to find particular individuals in the same spot every day.

Dangerously close. The male (on the left) was dispatched before he had the chance to mate, after a lengthy and careful approach.

Mating and cannibalism
Adult females are readily distinguished by their larger size and swollen abdomen. Females often cannibalise males (often right during mating), and males might die after mating a couple of times so at the end of the season, only mature females might remain.

Female Araneus diadematus with its fresh egg sac.  Once their egg sac is finished, the female sits on it and will die in a few days.

Egg sacs and spiderlings
Females lay their eggs, often over a thousand of them, and spin an egg sac around them. Females might die shortly after egg laying. The spiderlings hatch, moult inside the egg sac and then they emerge. In some species, like the garden spider, they spin a communal web and cluster together in it until they are ready to disperse.

A spiderling ball, newly born A. diadematus

At the end of the summer, full size Araneus diadematus can subdue quite large insects such as droneflies, butterflies and wasps.

A. diadematus are very variable in background colour with a range from sandy to chocolate brown, although the white markings on the abdomen tend to be more uniform.

A garden stretch spider!

It has been so pleasant today, warm and still, with high clouds. I had planned to do a little evening gardening and I was about to start trimming the olive tree when I noticed a busy spider web spinning. Wait, a stretch spider, Tetragnatha, a new spider for the garden! I rushed back home to fetch the camera and took some photos. I think it is a female, possibly adult. Her yellow abdominal stripe glowing with the flash. I couldn't bring myself to capture it for ID as I would have surely destroyed her web and spoiled her night hunt, so I might do tomorrow. I will update the post if I find out what species she is.

Christmas spider

A large volume of search keywords hitting BugBlog are about spiders. "Scary spider" in particular features high on the search keyword ranking. I hope the blog helps dispel the myth of spiders as scary bugs. I thought fitting to finish 2011 with a not very scary spider, one that most of the time is hiding outside on the corner of windows, doors and railings in a little silky retreat, and that weaves a fresh web every morning all through the winter. Zygiella x-notata, the Missing sector spider, or window-frame spider, makes characteristic webs with a missing section, though which its signal threat runs (top left hand corner). This one's web glistened on the sun today, with the backdrop of cotoneaster berries that the blackbirds haven't quite finished yet.

Window frame spider

Zygiella spinning its web on a garden railing

Suddenly, most of the summer bugs seem to have disappeared to leave your usual autumn suspects: wasps, a few Bombus pascuorum, garden spiders and plenty of flies. There is a common bug, though, that hangs on year round. It is the window frame spider, Zygiella x-notata. This species is an orb spider (related to the Garden Spider, Araneus diadematus) which spins its webs on gates, window frames, wheelie bins and other flat surfaces associated to human constructions. The web is quite recognisable, as it has a sector with no connecting threads in it, it is thought to be adapted to be built in such flat dimensions by keeping the signal thread free from getting tangled in the sticky connecting threads. The signal thread runs in the middle of this sector and allows the spider to detect any vibrations due to insects trapped in it. During the day, the spider hides in a silky tube on a corner, with the first pair of legs touching the signal thread that leads to its web. At night she is often seen either just outside the retreat or on the web, in a more similar way to garden spiders.

A Zygiella x-notata web on a garden gate. The spider's retreat is on the top right-hand corner. Note the signal thread and the 'empty' segment on the orb

This one used to live inside the kitchen window.

Eventually, she laid her eggs and spun a cocoon for them. She sat on the cocoon until she died.