This is what we found in our wheelhouse when we arrived just after dark today.
There were also quite a lot in the cabin but these were mostly dead and so easy to vaccum up.
Fortunately we came prepared. Flypapers, electric swatter, and vacuum cleaner. So we have cleared away nearly all of them (I think I can see only about 3 or 4 flying around the cabin at the moment).
We assume they are hatching in the wheelhouse support tubes, ideal breeding grounds?. It does tend to move updating the wheelhouse up our priority list, although really we want to wait for nice Spring weather for a job like that. Maybe we can just put some sealant in the ends to see if that reduces the problem?