Sunday, May 31, 2015

What's happening right this minute.

The eastern United States is the only place you can see periodic cicadas. They are one of the world's marvels, but the catch is you can only see them every few years, and then for only a few weeks. There are three species of seventeen-year cicadas, and four species of thirteen-year cicadas. As I'm sure you all know the name stands for the number of years they spend underground as nymphs sucking the juice out of tree roots. There must be so many millions of them it is another marvel that the trees survive. They don't all emerge together on the thirteenth or seventeenth year. All those in a certain population do, but the generations are staggered. They are so well studied that all the differing populations have been named and numbered, so that biologists can say almost to the day when population XI or whatever will come out of the ground, change into adults (leaving their thousands of exuviae hanging to trees and bushes) and the males start singing to attract mates. That's still another marvel, their loud voices constantly in hearing over sometimes a square mile.

We learned early this year that thirteen-year cicadas would be emerging this summer in parts of Arkansas. So I wasn't surprised when, a few days ago, I arrived in Craighead Forest Park in Jonesboro, turned off my engine and opened the door to hear that sound. It was the first time in years.

They were some distance away, and I was in a hurry that day, so I didn't pursue them. But the next day Cheryl and I went to another area where we had seen them in the past, Lake Hogue in Bayou de View WMA in Poinsett Co. Sure enough they were singing at full volume when we arrived. There seemed to be at least two songs going, a high pitched melodic one which appeared to be constant on the same tone, and then a raspier one that surged up and down in volume. We walked a dirt road and saw them flying out from the tops of the trees like swarming bees. Their life as mating adults is so short we were already finding dead and dying on the road and picked up a dozen or so to take home and study. They were different sizes and slightly different colors. We knew there could be up to four species but we had no idea what to look for to try to separate them.

We had looked them up before and only found charts with roman numerals to designate the different populations and cohorts and emergence dates and it was so confusing that it made our (or anyway my) head swim, which is why we had never got anywhere trying to sort them out. But this time Cheryl made us stick to it and try to get some bearings, and we made a second trip and took photographs more intelligently and collected specimens with a better idea of what we were looking for, and we believe we found all four species. (However this was our first attempt at identifying the species, the color differences are subtle, the dead specimens perhaps changing color rapidly.)

Here's what we found, and here is our rationale, but keep in mind that our voice is very tentative.

If you have ever seen them, you will remember their dramatic appearance: big shiny black insects with bright red eyes and yellow veins on their large wings (they should only emerge during Halloween). Look at this first one.

Here the critical thing to look for is the orange spot directly behind the eye. Next let's look at it from another angle.

The underside of the abdomen is pale orange or yellowish. If we are correct, this is Magicicada tredecim, which is a more scientific way of saying "thirteen-year cicada."
Now look at this mating pair.

One is dangling unceremoniously off the branch, but after waiting thirteen years for this moment nothing is going to make them let go.  On the sitting one you see a brown spot behind the eye; on the dangling one a highly contrasting banded underbelly.

Here they have regained their position and a little dignity. You can see on both of them the brown spot behind the eye, which I think is quite different from the orange spot behind the eye of the previous example. Again if we are correct, this is Magicicada neotredecim.

Those are large cicadas. The next two I'm going to show you are noticeably smaller. First, here is an all black one. (In the hand the eyes on this one were still reddish, though the camera has not picked that up.)

No colored spot behind the eye, no yellow bands on the abdomen. This, we believe, is Magicicada tredecassini. And finally, this slightly different species, all black, but with narrow orange banding on the abdomen.

We believe this is Magicicada tredecula.

These are active in Arkansas right this minute. If you are driving through dense deciduous woods, stop from time to time to listen. If you hear them (you can't miss the sound) get out and observe them. It will be a long wait before you see them again. Only thirteen-year cicadas are out in Arkansas this year. In some other states (Kansas, for instance), I believe there are some seventeen-year cicadas around. I think our corner of northeast Arkansas might be especially good for finding all four thirteen-year species together. I don't actually know if we get any seventeen-year cicadas.

There are three species of seventeen-year cicadas, each one a sister species (some would say the same species) to one of the thirteen-year cicadas, and it is almost impossible tell between the sister species except by timing and location.

If we get them, I can't wait for a seventeen-year cicada emergence.

Monday, May 18, 2015

In, on, and around the house

In the corner of my study a big very handsome Cellar Spider has been living for the past two or three years. She seems to feed quite well on spiders that wander into the house. She can catch spiders much bigger than she is by wrapping them up carefully at arm's length, which in her case is a good safe distance away.

 Lately she had been growing quite fat, which indicated she was filling up with eggs.

The local males had noticed this as well. Last week when I looked into her web, at least four hopeful males were hanging around in it. They were nervous around this spider hunter, and probably with good reason. You will understand why, when I explain some of the intricacies of spider mating. First note the male's heavy equipment on the palps on either side of his face. These carry intricate vessels that the male fills with semen when he is approaching a female.

Now here is the female from underneath.

The dark slit near the base of her abdomen has in its center the epigynum, into which the male (the female's deadly fangs hanging over his head) must pump the semen he holds in his palps. This risky maneuver is preceded by a great deal of stroking from the tip ends of his own very long legs, while he unfurls his apparatus and tries to judge her mood.

 Suddenly he dives in, does his job in less than a second, and dives away as fast as he can.

He was successful. In about a week she was cradling her new eggs.

About the same time the eggs appeared, Cheryl and I were outside and noticed what at first looked like a small ant walking along on the lid of our garbage can. But when we looked more closely, we saw it was a kind of jumping spider (Synemosyna formica) which mimics ants (no one knows exactly why, but perhaps it's because ants are known to be full of formic acid and therefore not very tasty to predators). This one walked along on six legs with an ant-like gait, and since, being a spider, it had eight legs, and no antennae, to complete its mask it carried its second pair of legs in the air and waved them like antennae.

On top of the lid near it was an ant just the size and color of the spider and so similar in appearance we decided this was the model the spider was imitating.

(This ant apparently led a warrior life; note the decapitated head of another ant which still has its jaws locked on this ant's antennae.)

From there we walked around the corner of the house not twenty feet and saw a completely unrelated spider (Two-banded Antmimic, Castianeira cingulata) which appeared to be imitating the same ant (only this time waving its first pair of legs like antennae).

And a few minutes later we had another nice observation. I went to check a chrysalis that was hanging on the back wall of my study, and a Question Mark butterfly had eclosed. It was so fresh it still had a number of delicate tints on its wings that would soon wear off.

Not a bad day, and we had scarcely stepped outside the house.

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.