Between 1982 and 1992 I worked as a research and advisory entomologist for the UK Forestry Commission based at their Northern Research Station just outside Edinburgh. For the first five years of my time there I worked almost exclusively on the pine beauty moth, Panolis flammea. The pine beauty moth is
a native insect that became a pest of a non-native tree, Pinus contorta, then a tree that was widely planted over northern Britain. The majority of planting in Scotland was in the north and this meant that my study sites were in Sutherland and Caithness and Aberdeenshire. My main experimental forest was west of Aberdeen in the Spey valley (very handy for the whisky trail) in the Elchies block of Criagellalchie Forest.
My experimental forest with nearby distillery marked 😉
In Mid-January 1984, I headed north to do some maintenance on my head capsule collecting funnel traps.
In those days, snow was a perennial hazard, even in the south of Scotland and as I progressed northwards the drifts at the side of the road became increasingly higher. When I reached the forest gates, it was obvious that I was not going to be able to drive to my site. The sun was shining, the sky was blue and the snow glistened. A perfect day for a walk, albeit one of 10 km. Luckily, the weather had been sunny for the last couple of days so the snow was mostly hard enough to walk on. Only in a few places did I break the surface and find that I was standing on about a metre depth of snow. Two hours later as I was approaching my field site, squinting against the sun bouncing off the white untouched snow, I saw black spots moving on the surface. My immediate thought was that I was suffering the first stages of snow-blindness, but as I got nearer I saw that the black dots were actually insects. At first sight I thought I was hallucinating, was this some strange bizarre form of life perhaps an aphid-fly hybridization experiment gone wrong? On closer examination I realised that I was looking at wingless Mecopterans.
Male snow flea, Boreus hyemalis http://mecoptera.free.fr/Boreus-hyemalis.html
Female Boreus hyemalis, note the sting-like ovipositor. http://www.wbrc.org.uk/WORCRECD/32/Bingham–John–Snow_Flea_Boreus_hyemalis.html
Although I was familiar with Scorpion-flies, I had never seen these critters before.
The aptly named Scorpion fly Panorpa communis : https://commons.wikimedia.org/wiki/File:Scorpion_Fly._Panorpa_communis._Mecoptera_(7837166610).jpg
I collected a few to send off for identification and confirmation and carried on into the depths of the forest to check on my funnels. On returning to civilization a day or so later I sent my specimens off to the Natural History Museum and shortly after was informed that I had they were the snow flea, Boreus hyemalis and that I had extended the recorded range of this particular species, albeit only by a few miles.
My record – it lasted 10 years as the furthest north before M.S.C. Elliott recorded it in February 1994 in Easter Fearn in the north-west Highlands.
Distribution of Boreus hyemalis in 1994; my record, then the furthest North.
Current recorded distribution of Boreus hyemalis – obviously widespread – just lacking people willing to go and look for it in the winter 🙂
So what is a snow flea. It is of course, not a flea, being a Mecopteran or Scorpion fly, albeit non-winged. In Britain there are three species with wings (in the genus Panorpa), the larvae and adults both being predatory on other insects. The adult snow flea is about 5mm long, and lives among moss on which it feeds as both a larva and adult (Withycombe, 1922, 1926). Interestingly, the BugLife site states that they are predatory in both the larval and adult stage. I am not sure where they got this information as they do not cite a reference and all the published literature I have seen indicates that they are moss feeders (Withycombe, 1922, 1926; Fraser, 1943; Hågvar, 2010). Indeed, Wthycombe (1922) conducted a series of experiments on the larvae and conclusively demonstrated that they were unable to complete their development unless fed on moss, although the adults will apparently also feed on dead insects.
These are true winter-active insects, adults emerging in October and November when they mate and lay their eggs the eggs at the base of moss plants), Polytrichium commune being the preferred host (Fraser, 1943). The eggs start to hatch in November and the larvae forage within the moss clumps, pupating towards the end of the summer, emerging as adults after 6-8 weeks. The adults, which are wingless, thus come out in the coldest months of the year, usually between October and April. They are most easily seen when walking or jumping on the snow surface. Considering that the adults are winter-active they have a surprisingly high super-cooling point (-6.5oC) (Sömme & Östbye, 1969), especially when compared with the cereal aphid, Sitobion avenae, which has a super-cooling point of -24oC but rarely survives English winters (Knight & Bale, 1986). The BugLife site wonders “how they (snow fleas) manage to jump up to 5 cm without muscular hind legs” but Burrows (2011) found that their jumping prowess is by virtue of large depressor muscles within the thorax which enables them to jump distances of up to 10 cm with a take-off velocity of 1 m s-1, indicating a force of about 16 times their body weight. So aptly named in this respect too.
The Snow flea is not found (or at least has not been recorded) in the mild south-west of Britain, seeming to prefer areas with a harsher winter. Climate warming may thus pose a threat for this intriguing and little studied insect. Perhaps it is time for us all to venture out in mid-winter and start scanning the surface of snow drifts in heathland areas for these elusive creatures before it is too late.
Fraser, F.C. (1943) Ecological and biological notes on Boreus hyemalis (L.) (Mecopt., Boreidae). Journal of the Society for British Entomology, 2, 125-129
Sömme, L. & Östbye, O. (1969) Cold-hardiness in some winter active isnects. Norsk Entomologisk Tidsskrift, 16, 45-48
Withycombe, C. L. (1922). On the life history of Boreus hyemalis L. Transactions of the Entomological Society of London, 1921, 312-318.
Withycombe, C. L. (1926). Additional remarks upon Boreus hyemalis L. Entomologist’s Monthly Magazine, 62, 81-83.
For more images and observations see http://www.wbrc.org.uk/WORCRECD/32/Bingham–John–Snow_Flea_Boreus_hyemalis.html