Ectopsocus petersi

If not our commonest barkfly then at least the one I encounter most often, both coming to light and found during the day.

The dark spots on the forewing vary in their strength and extent, and separation from Ectopsocus briggsi on sight is usually difficult, if not impossible. I recommend examination of the abdomens in order to reach a confident identification and find this very much easier if they are well cleared in 10% potassium hydroxide (or similar) first. A high-powered microscope may be necessary, espcially for females.

At the tip of the underside of males of both species there are several patches of dark tubercles, one close to the apex and, slightly basal to this, three in a row. You need to examine the middle one of these three (make sure you're looking at the right patch - I suspect that one or two of my earlier attempts at identifying these were confused due to looking at the patch nearer the apex instead). On briggsi this patch is narrow and, looking from the side, vertical-sided whereas on petersi it is broader and more rounded. There is some variation though, and on at least one occasion I have needed to revise my initial identification formed when using the dissecting microscope when I examined it under the compound microscope. Usually it is quite straighforward though...

This individual was pretty clear-cut - the patch of tubercles is top centre in the second photo and top right on the third photo.

male Ectopsocus petersi showing patch of tubercles from below and side, North Elmham (Norfolk, UK), 3rd September 2021

It can be useful to examine the internal genital structure too, especially on those individuals that are not so clear-cut. These can be difficult to isolate and clean without pulling the various elements apart, although so long as the elements aren't damaged that shouldn't matter. The differences between the two species' genitalia aren't covered at the excellent Barkfly Recording Scheme website, but they are covered by the RES Handbook by T R New (2nd ed 2005). However, there appears to be a mistake with the labelling here, as on page 98 figures 202 and 205 are referred to in the keys for petersi and briggsi respectively wherease the same diagrams (enlarged) appear on page 100 figures 214h and 214g where they are labelled as briggsi and richardsi respectively. I believe the text on page 98 is correct and the caption for figure 214 on page 100 is incorrect.

male Ectopsocus petersi showing patch of tubercles from below and two views of the genitalia, North Elmham (Norfolk, UK), 19th September 2021

On my first view the tubercle patch seemed to consist of a single narrow row of long tubercles with barely any 'patch', leading me to suspect it was briggsi, however on closer inspection there was a wider field of tiny tubercles than had first seemed to be the case; for the avoidance of doubt the genitalia clinched the ID as petersi.

male Ectopsocus petersi showing three views of the patch of tubercles and one of the genitalia, North Elmham (Norfolk, UK), 7th October 2021

male Ectopsocus petersi showing the patch of tubercles and the genitalia, North Elmham (Norfolk, UK), 24th September 2021

male Ectopsocus petersi showing the patch of tubercles (flat and from the side) and the genitalia, North Elmham (Norfolk, UK), 19th February 2022

male Ectopsocus petersi showing the patch of tubercles, North Elmham (Norfolk, UK), 30th December 2021

male Ectopsocus petersi showing the patch of tubercles, North Elmham (Norfolk, UK), 24th July 2021

It can be difficult to view either the tubercular patch or the genitalia while the genitalia remain inside the abdomen as even on a cleared specimen they can obscure one another when viewed through a bottom-lit microscope. But when well-enough cleared it may be possible, and has the benefit that you don't end up accidentally destroying the genitalia in the process of removing it (which is all too easy to do).

male Ectopsocus petersi showing three views of the patch of tubercles and one of the genitalia, North Elmham (Norfolk, UK), 24th June 2020

Even when only partially cleared you may be able to see enough to clinch the ID without removing the genitalia.

male Ectopsocus petersi showing the patch of tubercles and the tip of the genitalia, North Elmham (Norfolk, UK), 27th June 2020

Females can be tricky - the inner edges of the apical lobes of the subgenital plate are supposed to be parallel in petersi and converging in briggsi, however in my experience they are rarely exactly parallel on petersi and usually converge towards the apexes to a lesser or greater extent. Additionally the tips of these lobes have longer hairs on petersi than on briggsi, but this is not always easy to judge and is also subject to some variation (for example one individual I caught had long hairs on one lobe and short hairs on the other - apparently undamaged).

female Ectopsocus petersi showing apical lobes of the subgenital plate, Dillington Carr (Norfolk, UK), 15th November 2021

female Ectopsocus petersi showing apical lobes of the subgenital plate, North Elmham (Norfolk, UK), 25th August 2019

female Ectopsocus petersi showing apical lobes of the subgenital plate, North Elmham (Norfolk, UK), 26th October 2021

This female was short-winged (and tiny). The species is supposed to have a brachypterous form but this is the only one I've seen so it is presumably relatively unusual (although in view of their size they will be more easily overlooked, and in view of their short wings, presumably less likely to turn up in a moth trap). This individual showed more clearly parallel-sided lobes than usual, but the hairs on the tip of one of the lobes were shorter than usual, closer to briggsi.

brachypterous female Ectopsocus petersi showing apical lobes of the subgenital plate and together with a normal macropterous female Ectopsocus petersi (to its left - note that this picture was taken after death and the bodies are dried and shrivelled), North Elmham (Norfolk, UK), 8th December 2021

This was another tiny short-winged female. With the individual above I had assumed that the apparent difference in wing length between the photo taken when it was alive and the photo taken long after death was simply due to the body shrivelling up on drying out. But this next one seemed to grow longer wings while it remained alive so maybe that had happened with the previous one too? But the first photo was taken several hours after capture so you would think the short wings wouldn't be due to it having only just emerged. In any case, even when the last photos were taken the whole insect seemed smaller than is usual for this species.

brachypterous (?) female Ectopsocus petersi showing apical lobes of the subgenital plate, Gressenhall (Norfolk, UK), 28th March 2022 - the first photo taken on the day of capture and the others taken 5 days later

This female has a relatively clear central projection on the edge of the subgenital plate between the bases of the apical lobes - this is a character that seems to be more commonly found on briggsi where it can be very prominent. Notice also how the apical lobes are very short (the hairs at their tips are longer than the lobes themselves) - on briggsi the lobes are usually much longer (with hairs much shorter than their length). As with most characters, there is a degree of variation and overlap and identification is always best based on a suite of features.

female Ectopsocus petersi showing apical lobes of the subgenital plate, North Elmham (Norfolk, UK), 12th December 2021

There apppears to be a second pair of lobes which can be visible behind the first pair. So far as I understand it you only need to view the pair that is most easily visible.

female Ectopsocus petersi showing apical lobes of the subgenital plate, North Elmham (Norfolk, UK), 29th December 2021

The second pair of lobes was very clear on this one - sometimes, presumably dependent on the way the insect is angled, it could be possible to focus on the wrong lobes. The lobes behind appear to have longer finer hairs.

female Ectopsocus petersi showing apical lobes of the subgenital plate, North Elmham (Norfolk, UK), 29th November 2020

male Ectopsocus petersi, North Elmham Cathedral Meadows (Norfolk, UK), 6th March 2020