Collecting beetles from flood refuse

Although summer is often seen as peak time for entomology, many groups can be collected all year round if suitable techniques are used. This is particularly the case for beetles, as many species overwinter as the adult stage. The difficulty is that they may hide themselves away so well that finding them can be a painful task! Last year I demonstrated the benefits of tussocking, in which grass tussocks were excised and the beetles hibernating within were captured. This year I wanted to try a different winter recording method, that of studying flood litter. The general idea is that beetles that get washed out and caught up in floods will accumulate in the litter and debris that the flood carries along and deposits. You do have to wait for the opportunity of getting the right flood conditions, of course.

Most winters I had seen that the Gowy Meadows nature reserve was flooded, as the expanse of water was clearly visible from the M56. In mid-January this year we had snow, followed by rain and thawing, and I had checked with Steve Holmes, who visits regularly, that it was indeed flooded, as the Gowy had overtopped it’s bank and inundated the adjacent meadow. I gave it a few days to drain slightly and visited on the 27th January, hoping I had not been too late, as beetles can redisperse very quickly after the flood drains away.

Wellies were essential as Gowy can be a muddy site for most of the winter, so after wading through a quarter of a mile of six-inch-deep mud, hoping I would find something worthwhile, I came to the central meadow which was half-flooded. The water had receded slightly towards the centre of the meadow, and an interesting-looking ring of litter, mainly Juncus stems, had been deposited along the higher ground. This presumably marked the high point of flooding.

Not wishing to carry too much gear, I had simply brought a large lidded bucket and a pooter. The bucket lid doubled as a tray. I had suspected (and was correct) that the litter would be too wet to sieve effectively in the field, so would need to take a sample home.

Figure 1. Underside of a length of timber from flood litter at Gowy Meadows

Lying among the plant stem litter was a single discarded shoe. I wondered if anything had sheltered inside it, so I shook it over my tray and about 20 beetles fell out!  These were mainly small Carabids, Agonum, Acupalpus, Bembidion, and many small Staphs. I pooted up most of them then spent the next ten minutes tearing the shoe apart, every crevice yielding more specimens. In all I must have pooted over 100 beetles from the one shoe.

A little further along was a length of timber which had originally probably been a fence post. I rolled it over and the underside was covered with beetles, probably amounting to several hundred on the whole length. This is pictured in Figure 1. Several more strips of wood yielded similar results, with beetles on the surface of the timber, and more packed into crevices in the ends of the wood.  Judicious pooting selected many specimens, but as small species can rarely be distinguished in the field, it was necessary to take a good-sized sample.

Finally, I filled the bucket with randomly selected handfuls of the Juncus litter, as well as cautiously scrambling down the riverbank to recover some material that had accumulated at the margins. This is the sort of job you do very carefully if you are working alone.

Figure 2. Extraction technique by flooding

On getting home the contents of the pooter were easily sorted by anaesthetizing lightly with ethyl acetate. The bucket of soggy litter was more difficult to deal with. I partly sieved it, and put the sievings in the extractor. This revealed another selection of species, but I was convinced that most beetles were still sticking to the wet litter, so I used the flooding technique that is sometimes used for substrates like dung and carrion. A large container is half-filled with the litter, a sieve placed on top to retain it, and weighted down with a brick. The container is then filled with water, at which point many beetles float to the surface (Figure 2). Every half-hour or so I would skim off the floating beetles, drain them on paper, then sort them in a deep Petri dish under the microscope. Each sieveful would reveal more species. Finally, I removed the brick and sieve and pulled out handfuls of litter, swirling them in the water as I did so, to wash the beetles off. When all the litter had been removed in this way, the remaining water was poured through a fine sieve and another crop of specimens was recovered.

Figure 3. Laccobius striatulus (Hydrophilidae)

In total 115 species were identified. Some of the more interesting species found were:

Anommatus duodecimstriatus (Bothrideridae) (Notable A). This tiny (1.5mm) beetle can generally be found in rotting potatoes, and we do have plenty of potatoes in Cheshire. Despite this I could only find one prior Cheshire record, in SJ57 (Hatchmere area) in 1986.

Laccobius striatulus (Hydrophilidae) (Figure 3). A relatively common water beetle, but it seems to be largely absent from Cheshire. Guest and Harmer (2019) class it as extinct in VC58. Not any more apparently.

Limnichus pygmaeus (Limnichidae) (Nationally Scarce). A tiny water beetle that has not been previously found in VC58, according to the water beetle recording scheme (Foster et al. 2020).

Full species list
Acrotrichis fascicularis
Acrotrichis henrici
Acupalpus dubius
Agonum fuliginosum
Agonum thoreyi
Agriotes obscurus
Aleochara lanuginosa
Aloconota gregaria
Amara communis
Amischa analis
Amischa decipiens
Anacaena globulus
Anacaena limbata
Anisosticta novemdecimpunctata
Anommatus duodecimstriatus
Anotylus rugosus
Anotylus tetracarinatus
Atheta graminicola
Atomaria basalis
Atomaria mesomela
Atomaria rubida
Bembidion guttula
Bembidion minimum
Calodera aethiops
Carpelimus corticinus
Carpelimus elongatulus
Cartodere bifasciata
Catops morio
Cercyon granarius
Cercyon haemorrhoidalis
Cercyon melanocephalus
Cercyon pygmaeus
Cercyon sternalis
Chaetocnema hortensis
Chaetocnema picipes
Clambus pubescens
Clivina fossor
Coccidula rufa
Corticaria impressa
Cortinicara gibbosa
Cryptopleurum minutum
Dimetrota atramentaria
Dinaraea angustula
Ephistemus globulus
Euaesthetus ruficapillus
Euophryum confine
Gabrius breviventer
Galerucella sagittariae
Geostiba circellaris
Helophorus brevipalpis
Helophorus grandis
Helophorus obscurus
Hydraena riparia
Ishnosoma splendidum
Laccobius striatulus
Lathrobium brunnipes
Lathrobium elongatum
Lathrobium fulvipenne
Lathrobium longulum
Lesteva sicula
Limnichus pygmaeus
Longitarsus melanocephalus
Megasternum concinnum
Melinopterus sphacelatus
Microscydmus minimus
Mocyta fungi
Nephus redtenbacheri
Notaris acridulus
Ochthebius bicolon
Ochthebius minimus
Ocyusa maura
Omalium oxyacanthae
Oxypoda elongatula
Pachnida nigella
Paradromius linearis
Philhygra terminalis
Phaedon armoraciae
Philonthus carbonarius
Philonthus cognatus
Philonthus fumarius
Philonthus micantoides
Philorhizus melanocephalus
Phylotreta exclamationis
Platystethus arenarius
Poecilus versicolor
Protapion fulvipes
Psammoecus bipunctatus
Psylliodes affinis
Ptenidium nitidum
Pterostichus diligens
Quedius fuliginosus
Rhyzobius chrysomeloides
Rugilus erichsonii
Rybaxis longicornis
Stenolophus mixtus
Stenus bifoveolatus
Stenus bimaculatus
Stenus brunnipes
Stenus cicindeloides
Stenus clavicornis
Stenus juno
Stenus pusillus
Stenus solutus
Subcoccinella 24-punctata
Sunius propinquus
Tachyporus atriceps
Tachyporus dispar
Tachyporus hypnorum
Tanysphyrus lemnae
Telmatophilus caricis
Thinonoma atra
Trichocellus placidus
Tychius picirostris
Tychus niger
Xantholinus longiventris


Foster G.N., Bilton D.T., Hammond M. and Nelson B.H. (2020). Atlas of Water Beetles of Britain and Ireland – smaller families of Polyphaga.  FSC Publications, Telford.

Guest J. and Harmer A. (2019). The Water Beetles of Cheshire. Eds. G. Hedges and S. Judd, Tanyptera Trust, World Museum Liverpool.