#58 Water Scavenger Beetle by Jim Horsfall
Meet Jim Horsfall, Reserves Team Leader at Yorkshire Wildlife Trust!
Jim works on nature reserves in South Yorkshire, but grew up in the North near Skipton. He currently manages a wide range of sites, mostly in the lowlands, with a mix of grassland, heath, wetland, and woodland. His interests stem from an interest in fungi, but soon grew to include botany, moth trapping and looking for water beetles amongst other things. He is a member of Yorkshire Naturalist Union, Sorby Natural History Society, BSBI, British Mycological Society and others.
You can contact Jim at: Jim.horsfall@ywt.org.uk
Water beetles are not a natural group of insects (like ladybirds or butterflies), but instead are a group of disparate beetles that share a habitat. When dipping a pond net into a ditch, pond or puddle you could find any genus or species – one of the draws of this interesting group!
(c) Jim Horsfall
Jim’s chosen species is Berosus signaticollis, a species of the lowlands, often in ditches and pools in the Humberhead Levels. The Humberhead Levels the flat low-lying area that was Lake Humber as the ice melted at the end of the last ice age, and stretches from Doncaster to near York, and flows out of Yorkshire into the Humber estuary. Nationally this species mostly occurred south of a line from the Humber to Severn, but has started to stray over into the Vale of York and West Yorkshire, and has been moving north so is likely to be more commonly found further north.
Jim mostly looks for water beetles on his lunch breaks on the nature reserves he manage, and find this species relatively often, although it is scarce on a Yorkshire level. He has recently found the very similar Berosus luridus (only the second record for this species in Yorkshire since 2000), so by comparison this species is common. The species is usually found in shallow ditches and small ponds, in the marginal vegetation (amongst grasses and rushes).
The species is a Hydrophilid beetle, or Water Scavenger Beetle, of which there are many species in the UK. Like Berosus signaticollis, water scavenger beetles are mostly fairly streamlined in their outline to aid swimming through the water. The larvae are aquatic and can spend long periods underwater - Berosus species have gills as larvae. They then pupate and emerge as adult beetles with wings. At this stage Berosus signaticollis can move from the waterbody the egg was laid into, and so can disperse to find new habitat or stay put. The larvae are predators of smaller invertebrates, but as adults they are more of a scavenger, living off plant matter, detritus and probably a few invertebrates too. As an adult the beetles breathe air (they don’t have lungs but absorb oxygen through tubes in their body case), and so to stay under water they must take a bubble of air with them. The bubble sits under the hard wing cases on its back, which it comes to the surface to replenish the air every now and then.
The adults of this species can be found all year round and live for more than a year in many cases. This is a handy trait for anyone who spends much of the spring and summer looking for plants, and the autumn looking for mushrooms! Although there are fewer beetles in winter you can still successfully look for them at any time.
Identifying beetles like Berosus signaticollis is tricky. The largest diving beetles can usually be identified from a photo (take photos of top and bottom sides, as the underside has important features in many species), but at around 5mm long this species needs to be looked at under a low-powered microscope. The two black tic-tac shaped marks on the pronotum (the section between the head and wing cases) is distinctive, and you shouldn’t mistake this species for anything else (although sometimes the black marks are hard to see and lighting the beetle from different angles can help).
‘Having access to lots of suitable habitat on the nature reserves I work on and having opportunities to spend 10 minutes dipping a net means I have collected many records in the last few years since starting to record water beetles. They are a good group of species to tell you about habitat condition (there are some species that only like unpolluted water, others that tolerate some pollution). But checking livestock every now and then, and spending time dipping a net at the same time comes with its own challenges…our livestock are pretty inquisitive and want to know what is in the tray!’
Although there are species of water beetle that can persist in low water quality, the ubiquity of flea and tick treatments on dogs and livestock mean that many ponds are quite sterile. The insecticides used can persist on animals for weeks and wash off when they go charging into a pond killing many species within the water body. Turbid water (muddy from animals running through, again mostly dogs and where too many livestock have access to ponds) is also not good for water beetles. As a result, you are mostly likely to find good numbers of water beetles in clean water, unpolluted by sewage or agricultural run-off, and where dogs are excluded and where cattle are at low density or again fenced off from ponds. Yorkshire Wildlife Trust avoids using insecticides on livestock where possible and uses the least damaging ones when it must, so places their nature reserves are often pretty good. Fencing off a pond can be good, but a bit of disturbance is also beneficial, otherwise ponds can be choked by Reedmace or willows in no time at all – it is a fine balance.
To get started on looking for water beetles there are a few bits of kit you need. A pond net and a tray to empty sweepings into, some pots to put findings in, a stereo microscope and a couple of books (there are two Royal Entomological Society books that cover most species and are all you need). By spending a bit of time looking at what water beetles are where, it can lead to a much greater understanding of the little things (and to question the need to fence off every pond!) and to appreciate that although a field may look boring if looking for plants or other obvious species, it doesn’t mean there is no diversity there. There could indeed be something of great interest lurking under the water of a pond.
Recording and monitoring
If you do survey for and record water beetles, records can be entered via iRecord. These are actively verified by experts. Include a photo if you can and details of the size and distinguishing features.
Some atlases of the distribution of water beetles were produced recently, and drew on a wide range of records collected by volunteers, so when these are updated in future, your records will help to improve our knowledge of the distribution. As water beetles are much less popular to record than birds or plants, there is still an element of records and distributions are skewed by where recorders live and actively search for water beetles.
Further information and acknowledgements
NEYEDC would like to thank Jim for his time and expertise in helping to create this blog.