This is the time of year when lots of entomologists are staying indoors and turning their attention to specimens sampled earlier in the season. Fair enough because there is always lots of work to do and this can often be exciting because following on the heels of the AES exhibition there will be lots of new boxes and cabinets that need labelling and filling. To those new or relatively new to entomology this is a very rewarding way to carry on. Some might even consider the season over, or that with the temperature dropping and everything becoming damp and soft under foot and with the foliage impossible to sweep when it gets wet, it’s not worth the hassle. The option of staying indoors in the warm and identifying and carding specimens and printing labels and filling boxes or drawers with engineering precision is a tempting one. And at this time of year, especially for the novice, one bad outing can very effectively finish the season. Fair enough if you do not know better. The thought of venturing out at night is probably even more daunting because this is when it gets cold and dew settles on everything and so, unless a really good night can be had, the idea is usually quickly forgotten. Stamina also comes into play because it can be really enjoyable getting out on a warm spring or summer evening and staying out into the early hours, especially if, like us, it involves a trip to the local chip-shop and a bottle of decent chilli sauce is packed just for the occasion. No such treats during autumn or winter collecting though, which makes the stamina and determination to get out all the more elusive. Beyond this many people are simply not interested and so often you are on your own. Which can be miserable, especially if the trip is not very productive, and we have all had plenty of these, right? Even with the right company things can go wrong; on a few occasions I have enthusiastically tempted people out into the field at night only to find nothing worth the bother and to end up cold and fed up. So why bother with nocturnal collecting at this time of year? But we are made of sterner stuff and nocturnal collecting is a pleasure for us whatever the results and whatever the conditions.
The evening of 18/10/2014 taught us a very valuable lesson about nocturnal collecting i.e. just get out and do it and do not be put off by the occasional and inevitable bad experience. On that dark and delightful evening we decided to go to Croxley Moor, which is a few acres of local scrubland on which cattle are grazed during the summer and which has a really interesting mix of flora, to try to find Chrysolina marginata. This is a very local species which is usually considered to be rare and possibly in decline. The reason for this outing is that we had found a single specimen at this site a few years previous, at night when it was sitting on a dung pat, but we had not seen it since. Both adults and larvae are nocturnal and tend to stay close to the ground near to Yarrow, which is the host plant and which is abundant across the moor. This turned into an extraordinary night. Another valuable lesson learned that night was how advantageous it is to take a younger person with you, in this case it was my son Conall who was about twenty at the time and already an experienced and knowledgeable coleopterist, more importantly he has eyes like a hawk and can identify most common stuff at a glance. We began at about eight in the evening, both on hands and knees searching the rabbit-grazed turf by torchlight, and after trying a few likely-looking areas Conall found several specimens lodged tightly into the grass. During the next twenty minutes or so we (mostly Conall) found lots of the beetles, I mean lots and lots all within a few meters of turf. We soon gave up because we knew we did not have much time and we wanted to try some more areas for other species. To be honest we could have remained into the early hours but Croxley Moor does not allow that.
Croxley Moor is on a gentle slope which rises thirty metres or so from a chalk stream at the bottom to an area of turf and gorse and broom at the top, it is an SSSI and hosts a very diverse range of plants and insects including a micro moth that we discovered was only known from one other UK site (duly published), and the whole site is easily large and varied enough to provide a whole day of interesting beetling. But autumn nights pose a problem. At some time after dark a mist comes off the river, gets ever denser and then fills up the valley so that, from the top of the moor, you can see over the course of about two hours as it works its way up the hillside. As the mist rises the vegetation soon becomes wet and is useless for sweeping or beating and so the work needs done selectively and quickly. One interesting and rather disturbing aspect of this site, and always commented on by visitors, is that at some point as the mist is rising the cattle begin to wander and all that is visible is pairs of horns roaming about on a sea of fog! Anyway, we really wanted to search for a particular tortoise beetle and so we started sweeping Yarrow, and unavoidably also lots of Ragwort and long grass. It was immediately obvious we were onto something special. The most astounding thing was the huge number of flea beetles present, and among these many species of Longitarsus, Chaetocnema, Psylloides, Phyllotreta and Aphthona. And by large numbers I mean thousands of them, and the beauty of night sampling is that they do not jump, even under strong torchlight, they just sit there in the net and so the more interesting ones can be tubed. Also lots and lots of brentids and phalacrids, low numbers but lots of species of ladybirds including Hippodamia, lots of weevils; probably mostly common stuff but we found Graptus (a first for this site, at least for us) and Brachypera zoilus to be very common, along with Cryptocephalus fulvus, by sweeping low vegetation. Sweeping also produced plenty of rove beetles and ground beetles and, before the air temperature dropped as the mist ascended, a fair few dung beetles and plenty of Cercyon etc in flight. Further trips would no doubt have produced much more but we were not able to return for two weeks, at which time things had quietened down a little but there were still plenty of beetles to be had. The results from that evening surprised me so much that I rather excitedly emailed our Herts recorder (the late Trevor James) the following day only to be told that he had had a few similar evenings at other sites over the years during October. In my email to Trevor I likened the evening to one in spring or early summer, both in terms of specimens and diversity, and he agreed that the right night in autumn can be as good as any night in spring. For somebody new to beetles that evening would have provided enough specimens to become very familiar with a good portion of our fauna and also the enthusiasm to get out and do it again. At the time we were no strangers to crepuscular and nocturnal sampling and we had visited lots of sites to do so, probably as a result of lugging a moth trap and generator around looking for moths before we decided that beetles were more interesting, but that night on the moor was a real eye-opener for us and we can only wish similar magical experiences to other coleopterists who can muster the enthusiasm to get and learn more about their local sites. Chrysolina marginata is abundant on the moor but it is difficult to find, even when you know where to look, and it is crepuscular and nocturnal, and over the several years we visited the moor to both sample and to take samples for extraction etc, we only ever found it once before that night. It reminded us of a previous visit to the moor (early June) when we ran several moth traps, the old kind with 125W MV bulbs, and found Drinker Moths to be very abundant; they were everywhere, along with Elephant Hawks and all the rest of it, in fact we were often walking around with them in our hair and on our clothing, but when we returned early the following day there was no sign of them anywhere. Which goes to show that what you find during the day may well represent only a small part of the biodiversity of a site.