Birdbath Beetle (Helophorus brevipalpis)
For one afternoon my favourite animal was a Grooved Water Scavenger Beetle.
I mean, beetles are already a relatively niche interest (here in the UK at least), but a ‘grooved water scavenger’ one… what does that even mean?
Last winter, my dad and I decided to take on a more ‘rewilding-focused’ approach to managing the garden, and by the summer the garden was a jungle of unexpected species. The approach had certainly worked well for some areas, but the birdbath was in a sorry state: on the surface was a dusting of organic debris; at the bottom, a thick film of rust. I was about to fish some fallen flowerheads out, when I noticed a golden gleam moving beneath the muck.
A tiny, copper speck was shuffling about in the rust. Now that I had my eye in, I realised these little beasts were everywhere – swimming around, covered in muck, making the most of whatever nutrition they could find at the bottom of the birdbath. None of them seemed like they were in any hurry, and whenever they came up to breathe, they would get glued to the surface of the water by surface tension – if I hadn’t seen them diving already, I probably would have rescued a handful of the struggling individuals and felt really good about myself after! (It turns out that many Helophorus species are unable to dive from the water surface, and instead have to clamber down emergent vegetation)
My new friends turned out to be Grooved Water Scavenger Beetles (my best guess would be Helophorus brevipalpis) – a relatively common family of beetles with grooves down their elytra, which will happily colonise an ephemeral (temporary) pool. For those who can find ephemeral pools, such bodies of water provide abundant nutrients and warmth, without the hassle of predatory species. In fact, I didn’t see any other species in the birdbath (not including the countless microscopic individuals undoubtedly helping the beetles in breaking down the detritus). In case I hadn’t made it clear enough, these beetles are real opportunists – they’ll happily occupy any stagnant puddle, or rockpool, anything they can get their tarsi on!
Helophorus eggs are laid in the ground, in a silk-spun satchel with a spindly ‘mast’. The threads in the mast trap air, so that in the event of flooding the mast rises up out of the sediment, providing the eggs with oxygen. The larvae emerge and gorge themselves on invertebrates even smaller than they are, and after a couple weeks they dig a hole and pupate. Some beetles will then dig their way out of this hole, but my (frankly, rather lazy) beetles will wait for a downpour to break the earth open for them.
I think it was the unexpectedness of the discovery, the improbability that anything would have so successfully taken advantage of such an unlikely habitat, that really caught my attention.
So, yeah, for one afternoon, my favourite animal was a Grooved Water Scavenger Beetle – beat that!
Please note that not all British Helophoridae share the same life histories, and for the purposes of this post I have guessed that my beetles were Helophorus brevipalpis.
Many apologies to Grooved Water Scavenger Beetles for the assertion that they are lazy.
References and wider reading:
- https://www.ukbeetles.co.uk/ is an incredible resource for (you guessed it) UK beetles
- Angus, R.B. (1973) The habitats, life histories and immature stages of Helophorus F. (Coleoptera: Hydrophilidae). Trans. R. Ent. Soc. Lond. 125(1), 1-26