Sunday, May 31, 2015

Sawfly Refuge

While spending a pleasant afternoon in the backyard garden, the kids and I discovered a few of these "caterpillars" on a chrysanthemum plant. They are not caterpillars, but sawfly larva. The most obvious visual difference between caterpillars (which remember are butterfly and moth larva) and sawfly larva are the number of prolegs. Caterpillars have five or fewer, sawflies have six or more.
Sawflies are in the Hymenoptera, the bees, wasps, and ants. The adults most resemble wasps. Not all the larva resemble caterpillars, some species have larva with a definite grub-like look.
Since we found these initially on a chrysanthemum, I thought that must be what they were feeding on. But there was no evidence, no larva bite marks. Then I thought maybe they were eating plum tree leaves, and onto the mums from overhanging branches. But again no evidence of feeding, and no larva on the tree. The next day I did a bit of research, and found out that we had found European Pine Sawfly larva, Neodiprion sertifer While reading that they feed on the older needles of a variety of pines a light bulb went off in my head; a small Mugo Pine shrub in our yard had an distinctive pattern of defoliation; all the lower needles were missing. They had eaten the needles except the new growth, found at top. I had attributed this to rabbits feeding over the winter, though they had never touched it before - and I hadn't noticed any missing needles all winter. After a quick look over the Mugo Pine, I found another larva, some likely molts, and a lot of frass on the ground.
I think we found them away from the Mugo Pine because they had eaten all the old needles and needed to find a new pine to feed on. My kids took quite an interest in them. After trying to design a sawfly larva carnival(?), they placed any that they found under the swing set slide where we leave patch of grass unmowed as a bug refuge.
May 2, 2017 update I didn't notice any last spring, but they are back in full force this year.  I have to admit I've taken steps to remove them this time, but not before a got a decent photograph of an earlier instar