I eventually
turned the rock over, and found even more of the spiders and
M. pergandei corpses. Except for the first
spider we saw, all of the ones I noticed were females. In the photo to the
far right, if you look carefully you can see at least six
Euryopis. There were eight in my field of
view at one point. The rock with all of these females on it was right next
to the entrance of theMessor pergandei nest.
The ants were not as active as the ants at other nests at the time. They
were standing in a cluster at the nest entrance.
I wonder
if one of the reasons that Messor pergandei
keeps so many nest entrances is not because the granaries are full in the
nest below, as I read someplace, but instead is an attempt to dodge spider
infestations such as this.
I was in
Palm Springs, California on a business trip, I noticed a
Euryopis male dragging a
Myrmecosystus away from her nest. The area
around the nest was decorated with dead ants hanging from the vegetation.
The other Myrmecocystus ants stayed in their
nest, peering out as the Messor pergandei
did. The spider looked very similar, if not the same, to the ones in
Arizona. Another day, back in Arizona, I was looking at some
Pogonomyrmex californicus nests and I saw the
spider at the right walk across the midden and crouch beneath a rock. I
did not see it prey upon the Pogonomyrmex.
However, its proximity to their nest and the general "Euryopis"
look, makes me suspicious that it, too, was preying on the ants. I would
think that preying upon Pogonomyrmex would
make for a short, hard life.
2002-04 Update. Euryopis of what sort or another is far more common in the spring than I realized, amongst many species of ants. So far I've found Euryopis preying upon Messor pergandei, Acromyrmex versicolor (Leafcutter ants), Solenopsis xyloni (Southern Fire ants) and Pogonomyrmex maricopa (Maricopa Harvester Ants, here). I've put some photos of Euryopis preying upon Acromyrmex versicolor here.