Thursday, 1 October 2015

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.


Jodi said...

Very cool! I love the spiderling ball; I've never seen one. I'll have to find out what species local to me do this, and keep an eye out. Thanks for the neat post.

RayHolden said...

Amazing how the Arachtober thingy has developed from in 2008.

conall said...

This is great teaching - so useful and engaging - the information/explanations & the pictures are superb and at just the right level for people like me that want to learn but dont quite know the basics. I will def read them all and try to commit to memory (& bookmarks because my memory is not reliable) as best as I can!

Africa Gómez said...

Thank you conall, I am glad you are finding them interesting. I am using arachtober to learn more about all the families in the UK.

Africa Gómez said...

Thank you Jody, at the right time of the year, May and June here, these spiderling balls are everywhere. It takes a bit to spot them for the first time, but once you do, they become easier. This year there was a short stretch box hedge where I could count more than 10 spiderling balls and there was one even on my car!

Africa Gómez said...

Ray, yes, arachtober is growing, which is great as hopefully spiders become better known are people start appreciating them in their own right. I am glad arachtober is now everywhere!