Where do flies go in winter?

It was over to insect expert Eleanor Drinkwater from the University of York to answer this question from Chris on The Naked Scientists Forum.

Eleanor - Well so this is a really good question. You know there are around 7000 fly species in the UK and unfortunately most the airtime goes to, pardon the pun, go to houseflies or blue bottles you know the kind of big ones that we see buzzing around the place. So for a lot of the species that are much smaller and you don't necessarily notice, they’ll be active all year round but for the big fellas that you might notice, aren’t around this time of year they actually hibernate over winter. Say taking the housefly for example it'll have different generations will be living in breeding over summer, and then towards the winter those that get born just as it's getting cold, will then build up fat reserves and then will go find themselves somewhere cosy so it could be somewhere like, behind a picture in your house or in a nice corner and then they hibernate throughout the winter and then emerge when it gets warmer and then lay their eggs which is why occasionally in the winter you might find the odd fly like flying around your house you’re like “where did this come from?” And it's because maybe you've turned up the heating a little bit and it's suddenly woken up and it thinks it's springtime.

Chris - Usually in my case it's a mouse corpse in the loft.

Eleanor - Oh dear.

Chris - So the bottom line is then these things are there all year round some of them hang out by hibernating, by having laid down body fat, my mind is racing with the idea of an obese housefly. So they store up fat reserves for the winter and then they're ready to go when the spring comes the weather warms up.

Eleanor - If you look at a fly, which you might not have done but, you know, if you like bugs you might. In your spare time, if you look at the fly right at the end of its hibernation you know it might seem a lot more skinny then but then they quickly build up their fat reserves again after winter.

Chris - It's good to hear. Eleanor thanks.