I live on the sea front in Essex. We have a sycamore tree and an alder tree in front of us. For the last three nights at dusk there has been insect activity in and around them which has caused the seagulls to ' go wild' This continues for about an hour. The Insects, which look the size of large bumble bees, fly in and out of the trees but because of the light and height of the trees we cannot identify them ....... any idea please?
"The beetles are most active on warm, clear nights when the temperature is above 19C (66F). They emerge at about 8:30 pm, mate through the night, and return to the soil by daybreak. Beetles may return to the trees to re-mate several times over the mating period. Late in the period, the adult carcasses may litter the ground beneath trees used for swarming."
I'm not saying yours is that species; I'm just giving you a description of the evening swarming behaviour, which I know is not confined to that species. Chafers are part of the Scarabidae (scarabs in general). Your particular species might be a scarab that is not, sensu stricto, a chafer; just closely related. (I hope that's not muddied the waters!)
If I had to guess, I'd go for summer chafer, Amphimallon solstitialis