(Sorry for the ‘break in service’ – personal issues).
If swifts, swallows and martins rely on winged insects, or more correctly insects on the wing, then this seems to be a niche food source and thus more susceptable to changing environmental conditions. On the short theme of flies I can remember as a child having sticky lengths of ‘fly-paper’ hanging from the glass lamp-shade this covered with the dead and dying and still there would be dozens of flies buzzing around the room (part of the explanation given was the number of piggeries in the parish). Little wonder that swallows were abundant (I don’t remember seeing swifts until I moved to an urban environment). I don’t remember being then aware that when flies land on human’s food they vomit thereon although if that is Nature’s way so be it – this seems to have become a human paranoia, how much bulk can there be in a fly’s vomit and have we become so flimsy as to have no capability to cope with unfortunate inputs.
In terms of the food chain I think most fly varieties are omnivorous scavengers, but if they did feed on tiny creatures on the wing then what do those tiny creatures feed on, etc.
The Reverend Gilbert White (1720-1793) had comparatively little to say about insects compared with his wealth of observations and detailed correspondence related to birds, this mostly undertaken in his parish of Selborne, Hampshire where he was born, where he grew-up and where he served as curate. Selborne, now on the edge of the South Downs National Park, is/was about 20 miles from Southampton and the coast of the English Channel, an area he sometimes visited beyond his home parish.
The illustration above is of a ‘harvest-bug’ which White wrote about in March 1771.
(to be continued).