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spiders

140519-0621

We have not seen much dew in the Bay Area in this year of record drought, so here’s a reminder that sometimes there is actual moisture around here! On December 24, 2012 the sun lit up this tiny spider web among irises and Santa Barbara daisies.

140519-0623The spider that spun this web was no larger than a pin head, yet it contained enough instinctive knowledge to construct this complicated, 3-dimensional structure suspended expertly from  leaves and stems.

A typical organic garden contains thousands of spiders of many kinds. Most of them remain hidden in the vegetation, actively exploring for prey. Only a few spin webs that are large enough to be easily noticed.

The presence of spiders in the garden is ecologically profound, because they eat a significant fraction of the flying and crawling insects. In webs just like this one in the same garden, I have spotted fungus gnats, parasitic wasps, fruit flies, many other small insects, and even a lady beetle.

There are more than 42,000 kinds of spiders. They have been around for 400 million years, evolving from fascinating little critters called trigonotarbids that looked a little like modern ticks and mites.

Back in those early days there were no dew-spangled spider webs because web-weaving spiders had not yet evolved. True spiders with spinnerets appeared around 300 million years ago during the Carboniferous, a time when yard-long dragonflies cruised the skies. It must have been a great time to evolve predators!

There’s more about spider evolution at Wikipedia. There’s also a neat article about trigonotarbids.

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Every day this talented spider catches a tasty collection of flying insects. The web gets rebuilt, morning after morning. What a fantastically effective way to trap flies and other nutritious prey!

This is an orb-weaver spider, probably Araneus diadematus, yet another import from Europe. It is a female – the males of orb-weavers are quite small and difficult to find.

Here’s a great photo essay on A. diadematus, from Nick’s spiders of Europe. (Not one of my blogs, he’s another Nick.)

Males of this species make much smaller webs. If they find a female, they make their web at the outside edge of hers. Like most spiders, their mating is tricky. Males risk their lives as they make forays into the female’s web, looking for some arachnid nooky.

Later this year, she will retire from active trapping. If she’s lucky enough to have mated, replete with eggs she will find a sheltered place and lay her eggs, surrounding them with a sac of silk.

The tiny spiderlings will hatch out in the spring. For a while they will cluster near their birthplace, then spread far and wide. Each one lives two years, overwintering as a young, midsize spider.

A. diadematus is also known as the cross spider. In the picture above, can you see the white cross on her back?

I could not find any male web near this one. Did she find a partner?