Notes from Underground-frieldobs

         Notes from
                        Underground

Obsevations on Dorymyrmex insanus in Arizona
by
Dale Ward

In early September of this year, I was walking along a dirt road that follows Gardner Canyon in Arizona’s Santa Rita Mountains. It was dusk, and I noticed some strange looking galls on the leaves of a shrub. The galls were perhaps a centimeter long or so, and came off of the ventral surface of the shrub’s leaves. They were roughly conical, with a slight curve, and each looked remarkably like a witch’s hat. Many of the leaves on this particular shrub had the galls - I would guess a quarter to one-third of them.

On the upper surface of the leaves, directly above the gall, was a woody area, and the woody area had a slit in it. All of the galls that I saw had the upper leaf surface slit.

Then I noticed that the shrub had lots of ants on it – I believe the ants were Dorymyrmex insanus. There seemed to be two or three ants associated with each gall-slit. At least one ant would enter the gall through the slit. The other ants would put their heads into the slit periodically, as though they were going to enter as well, then they would back out. If one of them did enter the slit and there was another ant inside, one of the ants would quickly leave.

Periodically, the ant that was in the gall would put its head up to the slit and the ants on the outside would antennate it. I believe that they also exchanged fluids via trophyllaxis, but it was a bit too dark to tell for sure

At least one of the leaves had been eaten away entirely, presumably by a caterpillar, and all that remained of it was the leaf vein and the gall. The gall still had an ant associated with it, though.

A couple of times I saw the ants working at the woody edge of the slits, pulling off pieces. This made the entrance to the gall larger. In this photo you can see that the ant has some of the gall’s woody particles in her mandibles, and you can also see a pile of gall dust from previous renovations.

I took off one of the leaves and split the gall longitudinally. There was a Dorymyrmex, which ran away, inside the gall. At the apex of the gall there was a round button of an insect that I believe was a coccid. The coccid was secreting a drop of liquid (at the tip of the yellow arrow in the photograph).

Within thirty or forty seconds of me placing the gall on the ground for photographs, a Dorymyrmex came over and began to feed on the droplet of honeydew. In a couple of minutes there were three or four Dorymyrmex clustered around the droplet.

Here is a photo of the gall and the coccid taken at home. Both have been in alcohol for awhile, hence their less-than-fresh appearance. On the coccid’s ventral surface, there are what appears to be legs under the skin.

I would like to have seen the galls and the ants earlier in their cycle – was the coccid completely sealed into the gall until the ants opened the slit? How did the coccid get rid of its waste if it was sealed – does it rely upon the ants? Or did the slit only close up as the coccid reached the prepupal stage? I was most impressed with how quickly the ants found the coccid in the gall that I opened – does the coccid attract the ants?