Charlotte cocooning

European Garden Spiders, Araneus diadematus, have what is called a holarctic distribution, throughout Northern Eurasia and North America. They are quite large, with females measuring up to 20mm (If you are a regular reader you have seen them weaving their webs in my posts).

During most of the summer their bodies are huge and swollen, like this:

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But at the end of the summer it all changes. This new svelte female has laid her eggs in this orange cocoon, then woven a mesh over the top, and now guards them.

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Here you can see the orange egg sac more distinctly, and the surrounding white net:

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It is getting cold, and both these mothers will soon die, but the eggs (up to 800 of them each) survive all winter and hatch in the spring; I took this picture last May.

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Here is a close-up of the spiderlings:

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I think these common spiders must have been E.B. White’s inspiration for Charlotte.

The nerds among you might enjoy reading this detailed description of how she creates the egg sac and cocoon:

Before the female starts making her egg sac, she withdraws for several days. She then spins a thin layer of single, tightly-woven silk threads. The first layer is molded by her abdominal movements into a disk, known as a basal plate. Then she crawls underneath the basal plate and continuously turns around in circles spinning the cylindrical wall. The palps are held in contact with one side of this wall while spinnerets are placed on the opposite wall. After about two hours, the cylindrical wall grows to 5 mm in height. Cocoon size is directly related to the size of the spider, but not necessarily to the number of eggs it will hold. Females wait for a few minutes and begins to lay eggs and cover them in a tight pack of silk threads. This becomes the cover plate and the spider continues to add layers of thread to it. The loop mesh ultimately wraps around the entire surface of the egg sac. Females remain close to the cocoon for the next few days in case the threads need repairing. Females die a few days after the egg sac is built. The cocoon will appear unchanged externally while the spiderlings develop for a few months. The offspring emerge in spring and release fine threads of silk from their spinnerets to be carried off by the wind to new locations. Their journey through the air is called ballooning. Wherever each spider drops from the sky will be where its new life begins. (Dewey, 1993; Foelix, 1982; Preston-Mafham and Preston-Mafham, 1996)” from http://animaldiversity.org/accounts/Araneus_diadematus/ 

 

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