22 September 2012

Spiders! Orb Weavers

Now here is a spider with a greater sense of order than the previous sheet weaver.

She is a common garden spider (Araneus diadematus), recognised by the cross over her shoulders.

And here's something I didn't realise before ... orb spiders hang upside down. Nip outside and have a quick look at your spiders ... see? upside down. Wonder why.

There is a really interesting MSc thesis by Thomas Hellelberg of Aarhus university on the web [see what I've done there?] on how garden spiders build their webs. If you want to know more about it I strongly recommend you have a look.

Orb webs have distinct elements:

Which are evident in this image I've turned to black and white and inverted:

A     the hub
B     the free sector
C     the capture spiral
D     the frame
E     radii
F     spiral turns
G     mesh size
H     reverses

Scientists divide the web into 4 quadrants (I don't think the spiders do this, having not gone to school to study geometry), and it seems webs are consistently larger in the southern quarter with a more even mesh size and more radii in that zone. And this does seem to be the case in this web. 

I wonder if this is why the spiders sit facing downwards - prey is more likely to be caught in the better constructed southern area. Maybe I should ask Thomas.