Ilybius fuliginosus

Ilybius fuliginosus

Most of these were identified using Mike Hackston's keys but some of the recent ones were done using Duff. This appears to be one of the commonest diving beetles here.

Ilybius fuliginosus, Bintree Wood (Norfolk, UK), 13th June 2020

Ilybius fuliginosus, Wendling Beck Environment Project (Norfolk, UK), 20th August 2021

Ilybius fuliginosus, Wendling Beck Environment Project (Norfolk, UK), 21st June 2024

Ilybius fuliginosus, North Elmham Cathedral Meadows (Norfolk, UK), 18th July 2020

Ilybius fuliginosus, North Elmham Cathedral Meadows (Norfolk, UK), 30th March 2021

Ilybius fuliginosus, North Elmham (Norfolk, UK), 29th August 2018

Ilybius fuliginosus, North Elmham (Norfolk, UK), 30th August 2022

Typically I collect insects alive, pot them up and by the time I come to examine them they've already expired so there's no need to kill them. Usually this works fine, but occasionally they get covered in furry mould which can cause problems. On a few occasions they succomb to a different type of wet mould which causes significant darkening (and makes them smell awful and often fall apart). There wasn't much sign of that having occurred when I examined this one, but the beetle had nevertheless darkened such that I could no longer see any hint of the pale margins to the elytra (or the pale elytral epipleura). I knew from my live photo that it had had them, and so was confident that it was fuliginosus, but it prompted me to wonder whether if I was to examined another individual like this I could end up with the incorrect ID. So I used Duff to key this one and it would have led to Ilybius aenescens/guttifer, with the rounded tip to the median lobe ruling out guttifer. In fact, on removing the abdomen for dissection, the true identify would hopefully have become clear anyway, as in this case moving the elytra away from the abdomen so you could see light through them revealed the pale margins that had not been visible when closed against the abdomen.

male Ilybius fuliginosus showing side of elytron as it appeared when examined, same elytron backlit, metasternum, apical sternite, elytral sculpture and median lobe, North Elmham (Norfolk, UK), 28th July 2025