21st February 2019 – The Year of the Fly
A long time ago, when I first became interested in flies, my father, through his University contacts, got me set up with my very own colony of the fruit fly Drosophila melanogaster, that workhorse of eukaryotic genetics before DNA sequencing became trivial. I don’t think I managed to keep them going for very long, though I still have some of the glass tubes they lived in. Later, at University I learned all about the genetics of Drosophila eye colour, chromosome translocations and inversions and theories of speciation on Hawaiian islands.
Even later I started making wine from the fruits of the garden, inspired by the intense flavour and intoxicating properties of my parents-in-law’s blackcurrant wine. I tried blackcurrants and redcurrants from the garden, grapes from our greenhouse, birch sap from the woods and elder flowers from the lanes. There were occasional successes where guests didn’t choke on their first sip or leave their glass untouched, but in general the vintages were poor. Some were undrinkable, even for us, and for this the culprit was Drosophila. They could sniff out that alcohol was being brewed in the kitchen and drown themselves in the water-filled airlock. And when the airlock dried out, they were in with their bacterial-laden feet, and our wine would be turned to vinegar.
For the last few years I have been running a light trap in the garden in order to see what moths might be about. The answer was many more than I expected, more than 100 species each year, some unrecorded previously in that 10km square. Last year I experimented with attracting them using a treacle mixture smeared on trees and fenceposts, and attracted a slightly different set of moths (including the beautifully coloured and named Merveille du jour), but also slugs, wasps and flies. So why not use the same techniques for flies instead of pursuing them individually with a net – I could let the flies come to me.
Using a couple of drinks containers I constructed a primitive, but cheap, fly trap. The holes in the side of the bottom bottle let the flies in at the bait, and then those that flew upwards through the neck would become trapped in the top bottle as they wouldn’t find their way back out again.The obvious place to put the trap out was the compost heap which during the summer releases a cloud of flies whenever I peel back the carpet covering to add another bucketful of vegetable peelings, apple cores and coffee grounds. I baited the trap with slices of banana and felt very smug.
In the morning the banana was dotted with mouse droppings as I had just stuck the trap at the side of the compost heap. There were also lots of flies in the top bottle some of which I shook down into my laurel tubes. First to catch the eye were several long legged flies with spotted wings (two top left and one at the neck of the bottom bottle) which turned out to be Anispodidae (3. Anispodidae – the honey trap). Stuck between the two bottles was an unfortunate Trichoceridae (1. Trichoceridae – the ice house). And also a familiar stumpy fly, busy tracking back and forward looking for an escape – Drosophilidae. Which reminds me of the quip that although time flies like an arrow, fruit flies like a banana.