This picture was posted on a local farmers' Facebook forum but no one has any idea what they are. They are emerging from an old sleeper, and are roughly 5mm wide and the protruding part is about 2-3cm long. The sleeper is in Kent. We'd really like to identify them.
I have found out that the sleepers are made of oak, they were new timber when bought. I think they might have been imported from France? Quite a few lengths have fungi growing on them now. This particular sleeper is almost always in shade all year round and the wood itself is quite 'moist'. The far end of the sleeper that you cannot see has even more of these little critters coming out.
The owner of the sleeper has promised a close-up which I will post when received.
I have checked with my colleague who agrees that these are the empty pupal cases of crane-flies, he adds that he believes they are a species of Ctenophora, whose larvae develop in rotting wood. These flies are fairly common in southern England and also occur in France, but it is most likely these were bred locally in Kent, eggs being laid on the decaying wood. It is unusual to see them emerging in such numbers, looks like the railway sleepers have proved to be a superb food and habitat.