This Thanksgiving weekend Dan and I returned to the Toronto area for dinner with his family. The weather was gorgeous, and while there we took the dogs for a walk to a bit of natural habitat just down the road. The house is in a suburban area but backs onto a nice patch of woodland habitat, one of the largest such patches in the immediate vicinity, so there’s often some interesting goings-on there. I heard Carolina Wrens, which don’t really occur out here (they’re rare and very local), and Red-bellied Woodpecker which is also rare this far east but relatively common there. We have Northern Cardinals here but they’re sparse and in low numbers; down there, you hear them nearly every time you step out.
Despite that, there wasn’t a lot of time for naturalizing, but I did pause to ponder this tree when I came across it in a small meadow. It wasn’t the tree that caught my interest so much as what was going on with it: it was crawling with wasps. (The tree itself is a Scotch Pine, a non-native species that’s often planted in plantations or urban areas because it’s hardy and fast-growing. This one seems to have planted itself naturally.)
It’s a shame my camera doesn’t do video, because only video could have captured the numbers of wasps really well: the branches were alive with them, crawling between the needles and flying from one spot to another. There are seven wasps in this photo alone – multiply that by so many branches. I presumed that they were all converging on this tree because it was exuding sap for some reason, perhaps the way new buds are sticky to the touch. I wasn’t keen to stick my hand into the branches to find out if the twigs were sticky, however, so I just took a number of photos and then hurried to catch up with Dan, who by that time had made it halfway across the meadow.
But when I got home and started looking more closely at the photos, I noticed small brown bumps on the twigs. On some of the twigs, but not all of them. And the twigs with the most wasps seemed also to have the most bumps. Coincidence?
Some poking about Google and a quick reference of my Tracks and Sign of Insects, and I think I have an answer. I suspect these bumps to actually be scale insects, which are usually small, featureless domes scattered along twigs. They could be Pine Tortoise Scale, Toumeyella parvicornis, which is small and reddish and includes Scotch Pine among its targets. Like aphids, as they feed scale insects will produce honeydew, a sweet secretion resulting from their diet of sap. This honeydew, in turn, is very attractive to nectar-feeding insects such as bees and wasps.
The most common species of wasp on the tree was Eastern Yellowjacket, but I noticed at least one other yellow-and-black species, one mostly black species with a single yellow band, possibly two species of metallic green sweat bee, and the above, which I think is a species of spider wasp (family Pompilidae), though none of the ones shown in my Kaufman Guide to Insects or in the group’s photos on BugGuide seem to match. The Kaufman Guide does note about the family, though, that “Many visit aphid colonies for honeydew secreted by those insects.” Also present on the tree were quite a number of ladybugs. Ladybugs may be interested in the honeydew, but are probably there to feed on the scale insects themselves.