Crane fly season

Crane fly
A crane fly on my window last week

It's crane fly season here in West Yorkshire. Last week, we were suddenly inundated with them. One week there wasn't any sign of them, the next they were all over the place—particularly in the evenings.

I didn't know, until I looked it up, that crane flies spend most of their lives underground in their larval forms, which are known a leatherjackets. I knew that leatherjackets were very common round here, and are a favourite food of the local crows (particularly the rooks), but I did not know that leatherjackets transform into crane flies. You learn something every day.

I naturally supposed that crane flies emerge en masse to increase their chances of encountering a mate—which I still guess is right. But then I had another thought: emerging en masse will also give the individual crane flies a better chance of avoiding being eaten by predators: plenty more fish in the sea, so to speak. And then it occurred to me that they emerge in early September, which is about the time that swallows traditionally start heading south for the winter. Could the timing of the crane flies' emergence in September be an adaptation to avoid being eaten by swallows?

If so, it isn't a 100% reliable strategy. One evening last week, a family of swallows spent a good half-hour hunting around the west-facing eaves of my house. I initially mistook them for local bats—I had not seen swallows that close to the house before. I wonder if they were hunting crane flies, which appear to be attracted to the residual warmth of the building after sunset.

Writer and photographer Richard Carter, FCD is the founder of the Friends of Charles Darwin. He lives in Hebden Bridge, West Yorkshire.WebsiteFacebookTwitterNewsletterBooks
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3 thoughts on “Crane fly season

  1. Yes that is true. I can recall going on holiday to Scarborough many times and the start of Start of September there would a great hatch of Craneflies there known I understand as Jimmy Spinners or Tommy Spinners in parts of Yorkshire. These were the larger species such as Tipula.maxima rather the the Smaller T.juncia and T.palundsa normally hatching in Spring. Another interesting factor I have found is that further north one is the sooner these large Cranefiles emerge, so in Scotland late July to early August, in Yorkshire as you say September, in the South of England where I used to live October and here in Southern France where I now live as late as November.

  2. The one shown in your picture appears to be a female as it has a thicker abdomen with a point, not a sting as some people think, but its ovipositor.

    Generally the male is smaller and more fragile than the female and is a weaker flier. The male abdomen is thinner and has a blunt end. I also understand that once fertilised the females abdomen swells with its eggs. So if you see a large Cranefly with a fat belly it's Mummy-Long-Legs. It has to be said that although harmless as they neither bite nor sting the larvae Leatherjackets are an agricultural/horticultural pest as they eat the roots of grass, grain plants etc and cause bald spots on the laws of Cricket Pitches, Bowling Greens, the Greens of Golf Clubs, Gardens too.

  3. oh and i have just bought the Kindle version of your book and look forward to reading it.

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