miked's picture

Water beetles diving onto car

Observed: 10th June 2009 By: miked
iSpot team
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water beetles

water beetles that dived and died by the thousand onto a blue car. seen same thing in different parts of uk by floodplain meadows, why do they do it and in such numbers (other than just thinking its a pond). adjacent red car had none on.

Species interactions

No interactions present.


Martin Harvey's picture

swarming beetles

Glad you managed to get a photo of these tiny beetles. They were swarming in the garden of my local pub last Friday evening as well, so may be able to get a full identification once I've had a chance to look at them closely (assuming that mine are the same species as yours of course).

Swarming has been reported for Helophorus brevipalpis in the UK [Benham, B.R. 1975. Swarming of Helophorus brevipalpis Bedel (Col., Hydrophilidae) in north Devon. Entomologist's Monthly Magazine, 111, 127-8] - some other species in the genus do so as well, but brevipalpis seems to be the most abundant of them.

Helophorus brevipalpis swarming is also mentioned in:
Miguélez, D., and Valladares, L.F. 2008. Seasonal dispersal of water beetles (Coleoptera) in an agricultural landscape: a study using Moericke traps in northwest Spain. Ann. soc. entomol. Fr. (n.s.), 2008, 44 (3) : 317-326.

There is a wealth of fascinating information on water beetle dispersal in the above paper, and of Helophorus brevipalpis it says "[its] great abundance in the dispersal stage is related to parthenogenetic reproduction and the rapid production of a large number of colonising females", i.e. the swarms are largely composed of females dispersing to find new water bodies, in which they can lay eggs parthogenetically (without male fertilization).

They certainly can disperse - some of them managed to colonise my pint of beer last Friday!


Entomologist and biological recorder

miked's picture

Obviously Miguélez has not

Obviously Miguélez has not come across blue cars as they are much more effective than his silly yellow traps. the blue car got covered in many hundreds of the small beetles in a short while, in contrast the control red car beside it had virtually none. a second advantage is that the beetles instantly died on contact with the hot paintwork so no need for all that nasty ethanol. A third effect was that there were two other species of beetles, a medium sized one and a large one (a bit smaller than the big ditistucs) also hurtling into the blue car although these just bounced off rather than instantly dieing.
its perhaps also interesting that my locations were near rivers not still water bodies.

i am wondering whether 2009 will be the year of outbreaks, who wants to have a go at predicting the next one?

Martin Harvey's picture


My specimens from Buckinghamshire are indeed Helophorus brevipalpis, and they look identical to your photo, although we'd need to have one of yours under a microscope to be sure that they were the same (the species in this genus are very similar).

In the excellent Water Bugs and Water Beetles of Surrey Jonty Denton says of H. brevipalpis "ubiquitous in stagnant waters, and regularly found raining down on cars and other shiny surfaces in hot weather. It occurs in the meanest waters, such as silt puddles and leaf-filled puddles, but avoids heavy shading."

Elsewhere in the book Jonty mentions that red cars seem particularly attractive to water beetles, in contrast to Mike's experience here.

Entomologist and biological recorder

miked's picture

Might be interesting to hear

Might be interesting to hear other experiences of colours attracting insects. Definitely in the two cases of beetles and the blue car it was dark metallic blue that was most attractive, red and grey cars had almost none even though they were on either side of the blue one which had many thousands.

in contrast to this pollen beetles seem to be very attracted to yellow. in a previous job i was a researcher on yellow flowered crops and could never wear a yellow t-shirt as it would get completely covered in beetles, the other researchers had the same experience with different yellow flowered crops they could never wear yellow either.

there are reports that certain butterflies are attracted to blue.

charlieb's picture

Had a few (only 5 or 6) on a

Had a few (only 5 or 6) on a red car a few weeks back - all covered in silt and mud which made ID'ing a bit of a pain...

Nature girl's picture

Insect attractors

I'm a bit late entering this discussion, but have only just seen this post! It's very interesting that the beetles do this. I had a similar experience to Mike while at the Cambridge BioBlitz - the bright yellow t-shirts they gave us volunteers meant that I was covered in pollen beetles for the whole day. Maybe they were trying to boost the number of species found by making us insect attractors!

I think I have seen this phenomenon before with water beetles, but they were attracted to my trampoline which had a blue plastic rim around the edge. We always had lots of these beetles landing on it and I didn't think anything of it until now. I didn't even think that they were water beetles, but they seem to be similar to the beetles in this post so I suspect that they might have been the same species (or similar at least). Interestingly, I also remember frequently having water boatmen landing on the trampoline as well. I guess the black, springy material in the centre must look quite similar to a pond as it was quite shiny.