Friday, May 30, 2014

Geolycosa and Geometer

Back in 2011 we were on the prairie portion of the Jonesboro Nature Center when Cheryl discovered a Geolycosa missouriensis, and took this very nice photo of it:

Here it looks more like a gopher or some other small burrowing animal. In fact it is a handsome and very interesting spider. Geolycosa, 'earth wolf,' is the genus name for the Burrowing Wolf Spiders. We were especially delighted with it because Peggy Dorris in the 60's and 70's published, in several papers, her wide-ranging survey of the spiders of Arkansas, and she had not found this species, nor any other burrowing wolf spiders, among the 435 she recorded. So, in addition to being handsome, it was rather uncommon, not very well known, and quite interesting in its behavior. But we were concentrating on grasshoppers that year, and didn't follow up on it.

This year, the beginning of our second year on spiders, we went back, and checked out the prairie with burrowing wolf spiders in mind. Here is what we discovered. We had often in the past noted, when we were in this sort of terrain (namely a rather flat area with sandy soil and lots of bare ground), that there were round holes in the ground often with bright orange fresh sand from recent digging scattered around them. There were also lots of solitary hunting wasps around, and we assumed these were wasp holes, dug to deposit an egg in along with a paralyzed caterpillar or whatever host animal they specialized in. This year we examined these holes more critically. If you look carefully at the picture above you will see that the sand right around the mouth of the spider burrow has been tied together with spider silk. Well, we noticed that was true of most of these holes we were examining, holes that in size went from a diameter too small to stick a pencil in, to one that would require a quarter to cover it. Some even had dried plant material sewn into the sand, to make a little turret around the entrance.

When we saw these holes in the past, they were always empty, and so were they this day. But I decided to sit down and wait quietly by one, and see what happened. I'm not a particularly patient person, but I thought I would give it a full minute, counting out sixty seconds, one one-thousand, two one-thousand....

And as you can see in the picture above, before I reached sixty, legs began appearing down inside the tube and slowly rising to the surface. I very quietly raised my camera and aimed it at the top of the hole.

I made the tiniest movement, and it disappeared in a flash.

You see the pattern of this spider: a black body with gray hairs over the top, two-tone black and orange legs, and the chelicerae, the sort of mustache in front of the face, covered with yellow hairs.

I've described the habitat. Sandy soil, because sand is easy to dig in. The land mainly flat, but with some areas raised a few feet in elevation from the rest, or places with gradual hillsides, and those were the places where we found all the holes (often half a dozen in view at a time). Obviously a design to avoid flooding in heavy rains. The holes always appeared empty to us because the spiders are so sensitive to the least vibration in the ground, and have such sharp eyesight, that before we got close enough to see into the hole, they had already dived to the bottom. The one-minute rule, however, appeared to be standard for all of them.

To the north of Jonesboro in Greene County is Scatter Creek WMA. There is an area there of abandoned quarries which had all the proper ingredients, and when we checked it, it was similarly full of holes in appropriate locations. Here are pictures of one spider I waited by, keeping very still so that I didn't disturb it before it was fully out.

After the sixty-second count it was up just below the top. There was a cautious wait there, and then it moved up so it could see over the top. Another wait. When it felt completely secure, it moved its second pair of legs straight out in front, and that was its final comfortable position for surveying the landscape in front of it for prey. I didn't catch it in the act myself, but Cheryl was watching another spider on the side of a hill when she saw a small beetle trundling down the slope towards it. When it was four or five inches away the spider noticeably tensed, the beetle suddenly froze, then the spider rushed out and grabbed it and carried it back down into the burrow.

If you are a follower of this blog you might remember that I showed some pictures of another large wolf spider, Hogna carolinensis, which had a burrow with a similar turret, but otherwise their behavior is different. Many of the Hognas make burrows that they conceal themselves in during the day, then at night they come out and wander around looking for prey. Geolycosa comes out by day, sitting at the top of its burrow waiting for prey. I don't know this for sure, but I suspect they go back down into their burrows to rest during the night. There are other parts of their behavior I will try to learn more about this summer while I have these two big populations to monitor. My understanding is that at this time of year both males and females live in their burrows, but in late summer and fall, the fully grown males leave their burrows and go looking for females.

Now, on a different subject, look at this picture and tell me what you see.

Geometers make up a large family of moths. Geo, 'earth,' meter, 'measurer.' Its the family whose caterpillars are the familiar "inchworms," or "measuring worms," that progress by arching up their long bodies and sending the front of their body as far forward as it will go, then arching up their body again to pull the back half up to catch up with the front. But some of the caterpillars in the geometer group have a much more remarkable ability. They can hold their long bodies absolutely straight, and keep them stiff and rigid for hours at a time. To go along with this ability, often their markings precisely mimic the wood and bark and complicated joints of twigs. Birds feeding on caterpillars use the shape of a caterpillar as a search image, and caterpillars go to extraordinary lengths to break up that pattern and look instead like something inedible.

Last week we found (droppings underneath it provided a clue) what must be the world champion in this type is dissimulation. The caterpillar (that's what you were looking at) is on the trunk of a small bald cypress in our front yard. Several new cypress shoots are growing on the trunk at just that angle, in just that color and texture. Since we discovered it, we have been keeping an eye on it, and it holds that position all day long. It's been doing it for at least the week we have been watching it (a bird with a good memory might note that it is in a slightly different place each day.) Last night we finally remembered to go out and check on it at night.

Sure enough, that was when the caterpillar (we still are unsure of its identity) climbed up into the cypress tree foliage to feed.


  1. I've never even been that interested in insects or spiders, but your blog posts always fascinate me.

  2. I've been fascinated all my life, and that's just what I want to share.