The Flea that’s a Fly

What a way to start the year and my new life in the Cairngorms. I’ve got Red Squirrels regularly visiting the garden, Crested Tit and Crossbill just a five-minute walk away, Pine Marten have been seen in my street and I’ve even had a Golden Eagle fly over the garden. Things are pretty exciting to say the least.

The Cromdale’s are a smooth humped spine of hills that I can see from my house and on this day at the weekend they were heaped with snow. So against better judgement and without skis, I went for a walk up  ‘em. The snow was thigh-deep in places where it had drifted and progress through the virgin snow was picturesque but a struggle. I’ve never been a skier, but that is going to change because these conditions are exactly the reasons why skis were invented! As we crumped up the slope at a tedious pace (I would say glacial but that would imply we were going downslope) a couple of Mountain Hares were flushed, and a few Red Grouse were telling me to ‘go back’. The azure arch of the skies was tempting me to look up for Eagles but the going was so hard underfoot that looking up was for the foolish. Fortunately, there was a bit of a silver lining to this trip out and it came in the minuscule form of an insect.
A snow flea (Boreus hyemalis) to be precise and it isn’t a flea. It’s a Scorpionfly, which if you’re going to be totally taxonomically precise isn’t a fly either! But most of them, and we have 3 other species in the UK do at least have wings.

The Snow Flea doesn’t have any. It does have many of the other characteristics the most notable being a curved abdomen and a strange elongated head and mouthparts. But looking at these came later. It was just fortunate that I’m tuned into such subtle creatures. This tiny 3mm long speck in the snow could have been easily missed, but serendipitously it twitched at just the time my eyes were looking where to put my next foot. I immediately recognised it.
What ensued was a bit of overly childish jumping up and down. For this insect says winter mountains to me as much as any white hare or Ptarmigan and sadly most folks including those that spend lots of time in the hills don’t even know they exist let alone have seen one. Annoyingly for me – I didn’t have my macro lens with me and so I was only able to document this moment with my iPhone.

The other ‘regular’ Scorpion flies; the ones with wings are beasts of warm sunny hedgerows. They all look quite similar to each other, bedecked with picture frame wings. The males also possess a curious swollen genital capsule which is held at the tip of a slim abdomen and is curled back over its back giving it a threatening almost dangerous look reminiscent of a Scorpion. It is this that gives them their common name. Although quite frightening in appearance they are completely harmless.
The snow flea however doesn’t have the pretty wings or indeed the outwardly distinctive genitals. But look at its head and it has the other diagnostic feature of this family of insects – a long ‘face’. The elongated rostrum with mouthparts at the tip gives them all a recognisable profile.

A fly that can’t does sound like a bit of an oxymoron. However apterous it might be, it certainly doesn’t stop the Snow flea getting about which it does by a combination of walking and a surprising ability to jump – my little girl managed several jumps that must have got her clear of the snow’s crust by a good 5cm in a single bound.
Despite not having any obvious external adaptations for the saltatorial task of leaping, they have long legs and the use of an elastic protein called resilin which acts as an internal catapult. It is the same stuff that gives actual fleas their bounce too so this and the combination of their small size; around 5mm long explains at least part of their common name.

The other element of their name probably refers to the context in which they are most often noticed, as I did, against the contrasting bare backdrop of snow. Here they live for the most part in their mossy subnivean habitats (below the snow) occasionally gathering on the surface when the conditions suit them. While they don’t need the snow they do best in regions that experience a harsh winter.
Being insects they are ectothermic (cold-blooded) and cannot generate their own body heat. Rather than be at the mercy of the cold and its cell rupturing ice crystals – they have developed
the ability to supercool – a process by which they lower the freezing point of the fluids in the cells by the presence of special proteins and polyhydric alcohols, so that ice crystals don’t form and they cant freeze. Being able to be active with temperatures down to around -5 means they can move about, meet and mate all with minimum risk of being found and eaten by other predatory insects.

This female was lovelier than I imagined and after having initially caught my attention by simply being the only insect I’d seen active in the frozen icy landscape, I then took the opportunity to lie down on the snow to study her in detail.
The first notable thing that happened was my breath triggered her to fold up her legs and feign death. I didn’t know they did this. While she was in this state of thanatosis. The bright, low winter sun played off her body, reflecting a deep metallic green lustre.

I looked around for others like her but there was nothing to see just a vast expanse of frozen white. Where she had come from and where she was going I can only guess. I made a note of her position with the GPS n my phone and vowed to come back to look for others. A male would be nice as unlike her they do have wings – not any use for flying mind. Instead, the strange reduced appendages are almost spike-like. He apparently uses them to pin down the female, clamping around her head while in the throes of mating. Now that I’ve got to see. Who knows maybe I’ll find others in the future and next time get some proper photos?

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