International Rock-flipping Day

As mentioned in this morning’s post, today was International Rock-Flipping Day. This year’s event was being coordinated by Susannah over at Wanderin’ Weeta. I participated last year, as well, at our lake house. I think I always go in with high expectations of what I might find. I actually got a couple of interesting beetles last year. I was hopeful for something similarly interesting this year.

I started out by picking my location. There’s a small stand of trees, not quite large enough to be called a woodlot, but larger than just a group of trees, that has either grown up around the pile of rocks that was built when the fields were first cleared of rocks, or where the rocks were dumped. Either way, it’s a rocky patch of trees, while the surrounding fields are largely devoid of rocks. So this was the spot I targeted. Raven came with me to help me look. She did lots of sniffing, but not a lot of rock-flipping, however.

The very first rock I flipped had nothing under it. In fact, more than half the rocks I flipped had nothing under them. But the second rock I looked under had these three critters: a centipede, a millipede, and a sowbug. I’m completely re-writing this paragraph after realizing that the upper-right bug is actually a millipede and not a centipede as originally thought. How can you tell? The number of legs per segment: centipedes just have one, while millipedes have two (you can see these paired legs toward the lower portion of the critter). I had been thrown off by the fact that the millipede was flattened – ordinarily they’re cylindrical. It probably belongs to the order Polydesmida, which are all mostly flattened, possibly family Polydesmidae. I might even be so bold as to identify it to genus Pseudopolydesmus, which is the native genus of flattened millipedes (there are also two introduced flattened millipede genera).

The centipede is probably a stone centipede of the order Lithobiomorpha (as Hugh of Rock Paper Lizard translates for us, LithoBioMorpha = StoneLifeForm). The sowbug can be told from the closely-related pillbugs because it can’t roll up into a ball the way pillbugs can, and it has two “tails” on its rear end.

Other than those first three, and an earthworm that sucked itself back into its burrow at the sight of daylight, all of the rest of my living creatures were ants. First, there were these citronella ants. I wrote about citronella ants last year when I discovered a number of colonies “releasing their queens”. These ones scurried back into darkness quickly, and left no detectable scent.

This colony looked like it was maybe either just getting ready for, or just finishing, a reproductive flight. When I flipped over the rock a whole bunch of ants went scurrying, including half a dozen winged individuals, something I think you only see in ant colonies when they’re sending out flights. The ant two ants left from the winged one is carrying an egg. This is a more common sight when you disturb a colony. I tend to think of colonial insects as having their eggs all collected in special chambers, but these ants seem to be more casual about their location. You can see a few more eggs just inside the hole on the left.

This colony wasn’t doing anything interesting, but there sure were a lot of them. I don’t know what species any of these ants are. Species identification with ants is tricky and best left to the experts – I say this about a lot of insect groups. With ants, I can usually identify them to colour groups: yellow, red, black, red-and-black, and maybe, if I look closely, black-with-black-stripes. Size and ferocity of their bite is also sometimes helpful. Big black ant, little yellow ant, painful red ant.

Finally, I discovered this under a stone that was partially propped up on another rock. It’s not alive, but once was, probably last year. It’s half of the empty pupa of a Gypsy Moth. It’s identifiable as belonging to this species by its dark chestnut colour with golden-brown rings and golden tufts of hair. Just below it (which didn’t come through in the photo well) is the shed skin of the last instar of the caterpillar (I assume). Although Gypsy Moths can occasionally reach outbreak levels and become serious defoliators, I’ve never seen such destruction by the species here. I’m always delighted to find old cocoons, partially because I think the adults are neat to look at with interesting life-histories, but mostly because it’s fun to find evidence of something, know what it is, and know what had once been there.

Visit the official IRFD page at Wanderin’ Weeta for other rock-flippers and their discoveries.