Friday, May 8, 2015

Anelosimus studiosus

Last summer I noticed a messy scraggly spider web in some holly bushes down at the end of our driveway. It was three-dimensional, like a sock that had been pulled over the end of the branch, with a hollow space inside where the owner of the web could live.

I peered through the webwork to see if there was anything living inside. Finally I spotted a tiny spider (ca 3 mm.) and took a picture of it. With the picture downloaded I saw what I would not have seen with my bare eyes. The tiny spider was accompanied by a baby spider.

The tiny spider looked so much like a spider common in the garden (though not in such a big complicated nest) that I didn't pay much more attention to it. But in the middle of winter when things were quiet I was looking through pictures I had taken during the summer and studied this one more carefully and realized it was something new for the yard. According to my books, it was Anelosimus studiosus. So I changed the name on the caption, and was pleased to have a new species.

More time went by, then as I was reading a new book a friend had recommended to me, Biology of Spiders by Rainer F. Foelix (which says something about the kind of friends I have), I learned something amazing about this species. Now, as everyone knows, spiders are solitaries. They live separate from each other, and if they meet they fight to the death. Even during the times they have to come together for mating, the (usually smaller) males come with fear and trembling, and run for it afterwards as soon as they can. Well, it turns out that, of 40,000 named species of spiders in the world, only 31 species are considered to be "social," which is scarcely even enough to prove the rule. Anelosimus is one of them.

To call an insect or spider social in the technical sense, it's not enough that they live together without killing each other. For example, a number of kinds of spiders do live together, even sharing webs, peacefully, in sort of what might be called colonies, but that is not enough. You need to cooperate in keeping up the web, in helping the others kill food which is larger than any one of you could catch alone, you need to help with feeding the young, and you must be ready to give your life defending the nest.

All species of ants and termites are social in this strict sense. A handful of species of wasps and bees are social in the strict sense (thousands of species of bees and wasps are solitary). We are familiar with these social insects, but just the idea of social spiders seems amazing. We know something about bee and wasp hives and termite mounds, but how do spider societies operate?

I feel like I missed an opportunity to study these spiders last summer, because I did not realize they were something special. This summer I am going to make an effort to learn something about them.

I started this spring by searching our yard, and finding half a dozen nests. All the ones that were there last summer are still there, and are still being kept up. But I have found a particularly large nest in the backyard, and I am going to try to keep it under close observation. It won't be easy. The spiders are so tiny it is hard just to see them, let alone make sense of their behavior. The inside of their sock-like web is so full of sticks, dried flower stalks, dead insects, and other debris they can easily conceal themselves in it. Any photography I do is through the web, which obscures things. Also to photograph such tiny things I can get very little depth-of-field, so, when there are several spiders together its hard to get more than one or two in focus at a time, making the rest ghost-like out-of-focus apparitions. But I will try my best, and report my findings here.

Here are a few early attempts at photography (I hope I will improve).

This larger nest has at least six spiders living in it (I have seen that many at one time). All of them seem about half grown. I will be interested in seeing them work together to attack large prey that gets tangled in their communal web, and especially interested in seeing them feed their young. This varies among different species, from catching prey and letting the babies come together to feed on it, to regurgitating food into the babies' mouths, to, in the most extreme case, the mother slowly digesting her inner parts and offering them to the babies until nothing is left of her.

Their patterns are different enough from each other that I might be able to make a chart of how many different individuals there are in the nest by comparing the photographs, and then perhaps I can know which ones I am  looking at so that I can see if they differ in behavior. Termites and ants have carried sociality up a notch by evolving a caste system. There are huge muscular soldiers, medium sized workers, smaller minims to feed and raise the children. With the spiders in this group (there are other species of Anelosimus plus some near relations) individual spiders tend to be bold, and others timid. You don't see any difference in appearance, but the bolder ones (which biologists are now calling "warriors") are first to to come forward to capture prey, or try to drive off predators or parasites, and the more timid (called "nannies"), tend to stay behind and care for the young. I think it would be fascinating to actually observe that.

I already feel like George Schaller studying his lions or gorillas.

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