Wednesday, July 24, 2013

Behavior watching

You get your digital camera and your macro lens and you quickly find out what wonderful subjects arthropods make for photography. Then you realize what a learning tool you have, and you blow up the picture you have taken on your computer screen and hold it side by side with the illustration in your field guide, and you match the details, and then you learn the name of your subject, and you read up on it a bit, and then you go back into the field and watch your creature with new, informed eyes. It's a funny thing, but most of us don't really see something until we put a name on it. But once we do, then we are set up for the next stage, which is to begin observing it, really seeing it for the first time. That's when you can start behavior watching, and the very most fun of all, trying to record that behavior on your camera. Maybe in the end I will get a video camera (Cheryl is taking more and more movies on her camera, and perhaps I will try to put them on this blog if I can work out how to do it), but for now I am very pleased if I can catch a glimpse of some interesting behavior just with a series of still photos.

Insects and other arthropods have been fine-tuning their behavior for millions of years, and they are sometimes bizarre beyond belief. Here are a couple I have seen in the last few days.

We have a black walnut tree and a pecan tree in the yard. We don't get nuts from them. Our chief source of pleasure from them is that from time to time they have an outbreak of Walnut Caterpillars. These are wonderful large shaggy black caterpillars, and during an outbreak the tree can look like it has giant tent caterpillars without tents. (They don't by the way do any permanent damage to the tree at all.) Here is the caterpillar.

Here, multiplied by a hundred times, is what they look like during an outbreak.

Now some caterpillars with long hairs have stinging spines and it can be quite painful to touch them, but these do not. These are merely long hairs. They are, however, a first line of defense. It's very hard for birds, for instance, to swallow many of these ready-made hairballs without quickly clogging up their throats and stomachs. For the most part, it is only cuckoos who have the specialized techniques for eating them. And the long hairs also cause some problems for parasitic flesh flies and tachinid flies and the ichneumon and braconid wasps who try to lay eggs or larvae on the skin of caterpillars so they can bore their way inside and devour them from within. It's hard to get through the hair and down to the skin. But the caterpillars have a further line of defense which is quite amazing and amusing to see.

If an ichneumon wasp or a hungry bird turns up in among the caterpillars they all begin sharply jerking their heads and tails perhaps once a second. The wonderful thing is, the hundred or so caterpillars somehow synchronize the jerking, so that they make all their jerks at exactly the same moment. The effect is not of several small caterpillars jerking, but of one very large and perhaps formidable creature doing it. No one quite knows how these insects, with their poor eyesight, manage this precise synchronization with one another.

But that's only the beginning of their talents. Now, as they bolt down leaves and grow fast, from time to time they must pause to shed their skins. While they are shedding, and hardening up after their molt, they are soft, inactive, and very vulnerable to predation. They don't use protective colors to hide themselves, so a large aggregation of them can be seen from a distance. I described them earlier as looking something like tent caterpillars without a tent. Well, tent caterpillars have their tent to take shelter in when they are molting. What do the walnut caterpillars do?

I learned what they do when I came out the other morning and looked at our walnut tree and saw a big ball of some living thing down near the base of the trunk. Here's what it looked like:

And here is what had happened: Every caterpillar on the tree (if you look carefully you can see at least three different age classes) left the leaves at the top of the tree and climbed down to the bottom of the bare trunk and gathered in this ball. Again with magical synchronization, they had all come down to shed their skins at the same moment. As a friend suggested to me, instead of a single vulnerable caterpillar lying exposed, this resembled a big hairy animal.

I kept checking on this ball throughout the day, and as caterpillars hardened up and were ready, one by one at intervals five or so feet apart they marched back up to the top of the tree.

The next morning nothing was left but a bag of head capsules and empty skins.

A couple of days later we put on our headlamps and did a night op looking for spiders. I have reported before in this blog that on an earlier operation I found a small colony of Scytodes spitting spiders living in the siding of one corner of our house, and coming out at night to hunt. This is a frail, slow-moving, and, I imagine, rather timid spider that has perfected a hands-off method of hunting. They walk up close (but not too close) to a suitable small insect, point their fangs forward and they spit a mixture of glue and venom at it. They shiver their fangs, making a criss-crossing stream that envelopes their prey. By the time the prey begins to think it is in danger, it is already pinned to the ground with the venom sinking in.

Well, this night I caught one in the act. Mosquitoes around the house roost in large numbers on flat sheetwebs of spiders. They must land so softly and keep so still the spiders don't notice them. And being on the web must give them protection from most non-spider predators. But not this lone mosquito, which made the mistake of roosting on a scrap of Scytodes web.

In this first picture the spider is walking slowly towards the mosquito, spitting as it goes. It looks like a wing and a leg are beginning to get matted up.

In the second picture, slightly more from the side, you can see the chelicerae on the side towards us held out towards the mosquito, with the fang swiveled out (from this angle we can't see the fang on the far side). One wing and one leg are definitely tied up.

In the third picture the legs are completely tied up, the fangs still spitting. You can't actually see the stream of spit. For one thing, this is taken at night with a flash. But many years ago we watched in broad daylight as a spitting spider caught a fly, but we still couldn't see the stream, only little dots appearing where it struck the ground in a ring around the fly.

Let's look at the last two pictures from closer up to see more detail.

We didn't actually see the shivering of the fangs. We only read about that afterward. But the next chance we get, we will watch for that carefully. The more you observe, the more you learn. The more you learn, the more you actually see. For instance, the day after we saw the ball of walnut caterpillars here, we were out at Big Lake, and spotted a ball of walnut caterpillars at the base of a pecan tree there. Without our new knowledge, we would never have noticed it.

Wednesday, July 3, 2013

What's going on around the house lately.

In a blog devoted to invertebrates it might seem inappropriate to mention things with backbones, but our yard is completely overrun with tiny Fowler's Toads. They have only newly emerged from tadpoles and are about half an inch long, and they are in such numbers that as we walk through the yard they withdraw from us like a wave from an outgoing tide.

They're very cute, like characters in Winnie the Pooh. If you notice, the black spots on the the back each have half a dozen red warts in them, which is the sign that they are Fowler's, and not some other species of toad. I can't help wondering what effect they are going to have on the small wolf spiders in the yard, each of which would make a nice mouthful for them. [Update: I went out on a night op last night, making a round of the garden, and I only saw about a dozen pairs of eyes looking back at me. It was as if the yard  had been vacuumed. Maybe I need to devise a toad vacuum!]

Also in the yard right now are a number of Five-lined Skinks. Here is a male with his reddish jaws. The jaws are not as massive and muscular as those on the larger Broadhead Skink. But perhaps to compensate, these retain their blue tails into adulthood. Both Five-lined and Broadhead hatch from the egg with brilliant blue tails, which they flirt around, drawing the attention of predators, so that the losable and regrowable tail is seized while the front end runs away. When the Broadhead Skink matures, it loses it's blue tail. It is so burly and has such a powerful bite it probably doesn't need to rely on deception.

Not in the yard but not far away in the Joneboro Nature Center we saw this more colorful Prairie Racerunner. Like us these days he is covered with tiny orange chiggers. And a little bit farther away, on Hatchie Coon Island we saw this also colorful reptile, a slow-moving Mud Snake.

But now let's get back to small things, which should be our proper subject. In fact as compensation I'll bring up the smallest things we have seen. Here for instance at 1-2 mm long is a False Scorpion, false I presume because he has no venomous tail. They crawl around in the leaf litter and seize springtails with their claws, but from time to time they also climb to the top of flowers and when bees or butterflies land near them they hop on for a free ride to the next flower.

We had seen False Scorpions here before (not recently), so we weren't surprised. But we also found a brand new tiny thing that we had no idea lived here. I have mentioned before that my study is almost filled with Longbodied Cellar Spiders, sort of a daddylonglegs that will gradually fill all the space in a room with cobweb if you don't keep them trimmed back. I had read that there are other species of cellar spider, but most seemed to be found in the desert southwest. It took Cheryl's sharp eyes to realize there was indeed another species of cellar spider around, and in fact there was a population of them living right in the garage that my study is located in. There is a reason I hadn't noticed them: They are only about 2 mm long, which is to say, virtually invisible. They are called Shortbodied Cellar Spiders. They have the disproportionately long legs of the common Longbodied Cellar Spider that I live with daily, but they are still very close to being invisible. They are so tiny they are difficult to photograph. But the moment we got a good look at them we knew they were cellar spiders. You see, when the female cellar spider lays eggs, she puts them into a silk purse that she carries everywhere with her. She carries them in her jaws, and what is so distinctive about them is, she weaves her purse out of so few strands you can barely see the the purse, so the eggs are in plain sight. Here is a picture of our familiar Longbodied Cellar Spider carrying her eggs, and here is a picture (hugely enlarged) of our new Shortbodied Cellar Spider, also carrying her eggs in that purely cellar spider way.

Our usual cellar spider has the normal spider complement of eight eyes, but the tiny cellar spider only has six eyes. Unlike the Brown Recluse and the Spitting Spider which have six eyes (I have showed you pictures of them in this blog: They have three double eyes arranged in a triangle), the Shortbodied Cellar Spider has two triple eyes, the eyes appearing on each side of the head like "normal" eyes. You can see it in these pictures.

What else is new around here? Well, we always have good numbers of fireflies in our yard (all you have to do is have grass in your yard that you don't mow very much and of course never spray), and we know that the flashing of lights is mainly to attract males and females of the right species to each other, and when they meet they mate. But we had never thought much about the next step. But what seems to be common in our yard this year, and I don't know why we have never seen it before, is that we have female fireflies walking around on the ground, and they are walking because their abdomens are so bloated and distended with eggs that they can't get off the ground. Here's an example of one with its abdomen almost double its normal length (usually the abdomen does not extend beyond the ends of the elytra).

There's a smallish spider common in woodlands here called a Filmy Dome Spider. The web is characteristic: It has a tangle of supporting lines, and in the middle is a rising dome like an inverted bowl. I had tried in the past photographing it against a dark background, hoping that would  bring out the shape, but webs (unless they are covered with dew) don't show up very well in photographs) and I only got pictures with the vague suggestion of a dome in the midst of all the other lines. But the other day I was up at dawn and in the backyard there was a dome web between me and the rising sun, and the sun lit up every strand, and I finally got a fairly satisfactory picture.

Now we come to the spider of the month: the Asterisk Spider, so named because it makes a web of single strands sent out in all directions around it, so that it looks somewhat like an asterisk. I have never found the web, though I continue to look hard for it. The spider itself is impossible to find out in the woods (you will see why shortly), but I found this one hiding inside my empty garbage can. After I had photographed him, I placed him on a bush in our yard hoping he would be induced to make his web, and he immediately did his disappearing trick right before our eyes, resembling so closely a bump on a twig that if we had not seen him do it, we wouldn't have believed it. Unfortunately instead of making a web overnight, he simply left. But we got some wonderful bump-on-a-twig pictures.