On a spruce log

As I mentioned in the previous post, we left a stump standing when removing spruce trees after one fell in our backyard about five years ago. The stump has since become a very active place, with lots of bees, wasps, ants, beetles, and other insects making their homes there. At that time, being a bit lazy, I also left some spruce trunks and branches in a brush pile, rather than disposing of all of the debris. And that brush pile has since also become a great place for watching and photographing insects.

I first noticed small wasps (10 -12 mm) flitting about on the larger branches of the brush pile a couple of summers ago. They seemed to be nesting in the log, since I noticed some holes with what appeared to be sawdust piled beneath them. I managed to get a couple poor photos that I posted on iNat, which were subsequently identified by John Ascher as aphid wasps in the genus Pemphredon.

Well, they are back again this year. And I now that I know what they are, I'm able to spend some time observing them -- rather than just trying to get a picture to identify them. Previously when I saw them they were hard to observe or photograph, since they were constantly flying around and never seemed to sit still for more than a second or two. But yesterday they were much more cooperative.

There was one in particular that stood next to a hole in the log. It stood there nearly motionless for several hours -- at least it was there every time I came out to check on it. A couple times when I was watching, another Pemphredon would poke its head out of the hole, at which time the guy (I'm thinking it's a male) appeared to get all excited, tapping his antennae and moving about near the hole. The other wasp would generally go back into the tunnel and then completely emerge a few minutes later. As soon as the wasp left the hole, the waiting wasp would pounce on it for a split second, before the other wasp flew away. I don't think any mating occurred the two times that I observed this behavior. Perhaps the other wasps were males, rather than a female that waiting wasp was waiting for. I never saw a mating event, but I'll keep checking and maybe I (and the waiting male) will get lucky on another day. (It was rainy today so there was no activity.)

While watching the aphid wasps, I noticed some other small ichneumonid wasps (~ 13 mm) flying around the the spruce log. I managed to get a few pictures of them, which I posted to iNat. BugGuide identified them as Perithous scurra subspecies neomexicanus, saying, "The host is an aphid wasp in the genus Pemphredon.

So these little ichneumons are hanging out around the spruce log trying to parasitize the aphids wasp nests! Tomorrow I'll be hanging out there as well, if the weather improves a bit.

Posted on June 19, 2018 04:44 AM by swells