Tiny Sawfly with Forked Antennae

2022 August 14

This very tiny insect was crawling on our kitchen counter on August 13, 2022. It was in the “gnat” size range (maybe 4-5 millimeters long, about the size of a fruit fly), and was too small to easily see details with the naked eye. I could just barely make out that there was something weird with the antennae, but once I got the pictures with the macro lens it was pretty clear that the weirdness was that it appeared to have four antennae instead of just two.

Looking a bit closer, we can see that there are just two antenna bases, but they fork almost immediately. This is pretty unusual, I’ve never seen antennae like this before, and it is clearly a key ID feature.

I thought it was a fly (in the order Diptera) at first, but Diptera only have two wings, and this one looked like it probably had four. I wanted to get a picture of the face, but it had the really annoying habit of turning away from my camera every time I repositioned it, or I moved myself. At one point, I had it perched on a Ziploc plastic bag, and I kept spinning the bag to get it to face me and it would spin back the opposite way as fast as I could turn the bag. But anyway, what I could see of the face looks more along the line of a wasp than a fly, so I figured it was quite likely something in the order Hymenoptera.

And, after rummaging around for “hymenoptera forked antennae”, I tracked it as far as the sawflies in the subfamily Sterictiphorinae. It turns out that the males of some of the species in this subfamily have forked antennae just like that, and they tend to be on the smaller end of the size range.

It’s not a positive ID, but this one does look a great deal like a male Purslane Sawfly, Shizocerella pilicornis. The size and shape are about right, and the coloration is close at least. And the food plant is purslane, a low-growing plant with fleshy leaves that grows in some quantity around here. The larvae live in mines inside the purslane leaves.

3 Responses
  1. August 17, 2022

    Great stuff as always.

    I wonder what it was optimizing as it turned away from the camera.

  2. August 17, 2022

    I think it was either reflexively turning to face open air (maybe so that it could take off in an emergency without hitting anything?) or it basically has a little “gyroscope” in its brain that makes it want to hold position when the object it is sitting on moves.

  3. October 16, 2022

    I would bet it was the open air sensor. The gyroscope idea is pretty cool, but that would make it constantly shuffle around if it was resting on a leaf in a mild breeze.

Comments are closed.