A bit of a mystery, this...
A few evenings ago, I was watering my 15-year old grapefruit, grown
from pip, which lives in a pot sheltered up against the L-shaped front
wall of my house. Having soaked the pot, I sprinkled the foliage, only
to raise a swarm of black flies (as in house flies, but slightly
bigger, just under bluebottle size, and a blacker shade of black).
Why oh why would black flies shelter in my grapefruit foliage? I'd
never had this experience in the previous 15 years!

Cat(h)