Sawfly Larvae

2014 July 5

Today, we have three different sawfly larvae. These look superficially like butterfly/moth caterpillars, but are actually more closely related to bees and wasps (and you can tell what they are from the fact that they have too many legs, and often have very un-caterpillar-like eyes). The first one is a light green specimen that we got off of our mulberry bush on July 12, 2013 by putting a sheet under the bush and hitting the branches with a stick.

We can tell it’s a sawfly, because it has more prolegs than a butterfly/moth caterpillar would have.

Unfortunately, since it is immature, and mulberry doesn’t appear to be a common foodplant for sawflies, I don’t know what it is. It looks like it could be one of the “common sawflies” in the genus Allantus (in particular, it looks a lot like the ones referred to as “rose sawflies”, and mulberries are somewhat distantly related to roses), but take that with as large of a helping of salt as you like.

This dark green one came off of the same bush. Unlike the previous one with its dry, powdery skin, this one looks like it might have a thin slime coating. Again, while it looks superficially like a butterfly/moth caterpillar, it has more than 5 pairs of prolegs and so has to be a sawfly. Although, it has one fewer pair of legs than the previous sawfly did. But that’s OK, different species of sawfly have significant variations in their number of legs.

Unfortunately, I’m not having much luck narrowing it down much farther than “a sawfly”. There doesn’t seem to be much information about any sawflies eating mulberry, and the lack of distinguishing markings is making this one difficult. So, we may have to give the ID a miss in this case.

This third one was a bit different: it was a powdery white color, and was found later in the season (October 10, 2013), on one of the alder bushes that grow beside the trail through our back yard.

The head (particularly the eye) doesn’t look very caterpillar-like. I’ve never seen a moth/butterfly caterpillar with such distinct eyes.

The white doesn’t appear to be its base color. It looks like wax, being exuded from glands along its body.

There are apparently many species of sawfly that exude this white wax (in fact, the first one on this page was probably going to do so when it got older), which complicates identification. Normally, to identify the larva one has to know what plant they were eating. Luckily, in this case I’m pretty sure the plant was alder, making this the Alder Sawfly, Eriocampa ovata.

Whoop. I had thought this one would be a native species, since it is a specialist feeder on a native plant, but BugGuide says they are an invasive from Europe. But, since alder is not considered an economically important plant, these sawflies aren’t raising much concern. It also says they are parthenogenic in North America – apparently the original accidental introduction from Europe was only females (maybe only one female). This is backwards from the normal sex determination in their relatives, the ants, bees, and wasps: most of their relatives have fertilized eggs hatch as females, while unfertilized eggs hatch as males. In this case, it looks like these sawflies have swapped things, so that the unfertilized eggs are the females. So they can get along quite well without males if they have to. Although this does really suppress their genetic diversity, which could be a problem in resisting disease or adapting to new predators or changing conditions.

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