Chaoborus flavicans

I'm currently attempting to identify all of the craneflies I get to light at the Wendling Beck Environment Project and I collected this thinking it was - or at least might be - one of the smaller craneflies. In some (but not all) ways, to my relatively inexperienced eyes I thought it looked rather like a Molophilus, for example. Keying it as a cranefly quickly led to a dead end because the wings only had one anal vein (unlike Molophilus and most other craneflies that have two). ObsIdentify had also thought the insect might be a Chironomid but turning to the key to Chrironomidae this didn't make sense. In the end I dug out the fly family key and that's where I got it to Chaobidae.

Once identified to family I used Mike Hackston's key to that family to identify it to species. At first I wasn't sure if it might be Chaoborus crystallinus as I couldn't make out any bands on the abdomen when looking at it under the microscope (unfortunately in my only photo of the live insect the wings cover the abdomen). But the abdomen wasn't dark and I couldn't make out the dark area at the rear of the pronotum supposedly shown by that species. If I took the abdomen to be banded it keyed to flavicans but if there were bands they were really indistinct. I wasn't sure and thought I would have to leave it unidentified, until I noticed a thumbnail of my photo of the abdomen - at this small scale the bands were really clear! Sometimes it helps to take a step back and look at something without the aid of high magnification! The wing was 3.6mm long.

Chaoborus flavicans showing wing, tarsus, antennae, side of thorax (wings removed) and last few segments of the abdomen from above, Wendling Beck Environment Project (Norfolk, UK), 27th June 2024

These three came to light and, like the last one, I retained them thinking they might be craneflies. It was a busy timed session so it was eaiser to pot them and check later than make sure during the survey. Fortunately these aren't usually too time-consuming to identify so no bad thing to have some extra by-catch.

Chaoborus flavicans showing side of thorax and abdomen from above, Wendling Beck Environment Project (Norfolk, UK), 25th June 2025

second Chaoborus flavicans showing side of thorax and abdomen, Wendling Beck Environment Project (Norfolk, UK), 25th June 2025

The third was slightly larger than the other two and had more distinct stripes on the scutum but less distinct white sides to the thorax, prompting me to suspect it might be a different species. Checking I'd got it to family correctly I mistakenly thought I could see vein M-Cu (I was looking at the wrong vein!) and although I was pretty sure the palp features weren't right, checked it against the Culicidae key just in case. That led to genus Alopheles but the coxites weren't right, so I returned to Chaeboridae and once I was sure I was in the right family the only option that fitted seems to be flavicans again.

third male Chaoborus flavicans showing wing, scutellum, top of thorax and coxites, Wendling Beck Environment Project (Norfolk, UK), 25th June 2025