Identification, Images, & Information
For Insects, Spiders & Their Kin
For the United States & Canada

Unidentified sawfly larvae on grass

At the suggestion of Beatriz Moisset, I started going through the Unidentified Sawfly Larvae gallery looking for host plants that I (as a botanist) might recognize. I did spot several plants that I could identify, including dogwood, raspberry, dandelion, aster, and grasses. Of special note was the following series of images occurring on grass:

(Actually the last one on the right is dandelion, but it often occurs in lawns and fields with grass where the larva may have climbed up the "wrong" plant. My reason for including it comes next.)

The images come from Washington, Oregon, Michigan, Pennsylvania, West Virginia, and Maryland and each one features a different species of grass, but when I compiled them together, the larvae appeared to strongly resemble each other. Are they possibly all the same widespread species?

In wheatfield in Saskatchewan

duplicate comment





New Hampshire

they look alike but, pictures
they look alike, but pictures can't always be accurate

Addition from Ohio

Another from Ohio

Addition from NJ

I was guessing mine Dolerus.

Dave identified most of these as genus Dolerus,
but as yet they haven't been moved. We don't know if we are waiting for something more, or if no one has simply gotten around to it yet.

grass-feeding sawflies
Most all grass-feeding sawflies are in two genera of Tenthredinidae, Dolerus (Dolerinae) and Pachynematus (Nematinae). A few others, e.g., Eutomostethus and Paracharactus, are questionably recorded from grasses, or grasses and sedges, but not many. In North America, there could be 35-40 species of Dolerus and 30 or more species of Pachynematus associated with grass. Out of these, larvae have been described for perhaps 6 or 7 species – several of which are of minor importance in wheat or grain crops. With so many “unknowns” it is impossible to identify any of these grass feeders.
Since most are in two genera, a generic assignment can be tentatively made. Dolerus larvae have an asymmetrical labrum and prolegs on abdominal segments 2-8 and 10. Pachynematus larvae have a symmetrical labrum and have prolegs on abdominal segments 2-7 and 10. These are the main characters. For species, not much can be done at present. Most of those in the pictures appear to be species of Dolerus.
So far as I know, all grass-feeding sawflies have one generation a year. Larval development may take around 3 weeks. They are very difficult to rear and not of much economic importance, which is why they have not been studied.

How long
would it take for one to molt to the next instar or pupate? In the spring I found a lot of them sweeping the grass/clover to feed my spiders. I only kept one (they are a lot of food compared to aphids or springtails). It converted grass-to-frass for a long time, then it stopped. I keep taking out the old grass and adding new. Misting once in a while, but all it has done for a long time is lay there. If it is nudged it wiggles a bit and then stops.

I think that it depends on species
Some have only one generation a year and you have to provide the right conditions and wait until the next spring. That is what I am doing with this larva. I am pretty sure that there isn't a chance with only one specimen; it would have been nice to keep a good number of them but they all died.

I'm not sure if I'm that patient or if I could maintain the proper conditions for that long. With it in its "sleepy" state releasing outside probably wouldn't work. So it seems my choices may be back to spider food or maybe a month in the fridge and then back out to see what happens.

hey those look like mine
i recently posted some sawfly larvae that look like that and were found on grass too.

mine is from new hampshire.

I know picture-matching is not a strong identification technique, especially when a genus (or higher grouping) consists of many similar-appearing species, but I stumbled across this photo of a larva identified as Dolerus nitens on a European website named "The Ecology of Commanster" (a village in Belgium) and it reminded me of the ones that I compiled in the above collection. The caption there identifies grass as the larval food plant. Not jumping to conclusions, but maybe there is some relationship?

Some bad IDs
I have seen a few misidentifications on that site. The adult is plausibly a Dolerus ("looks like" one but I don't know sawflies). The association between adult and larva is not explained.

I found two more images in the "unidentified" gallery with grass reported as the apparent host plant:

Or maybe they're multiple related species with similar appearance and hostplant preferences. It will take an expert to sort it out.