Many people will be familiar with the large, biting flies called Horse or March Flies. They are in a family called the Tabanidae and, rather like mosquitoes, most of the females require a blood meal
before they can successfully reproduce.
I recently pulled one out of the pool (see image) and was able to identify it as Scaptia auriflua. Unlike most in the family, this species does not feed on blood, but rather on the nectar from flowers. A good tabanid fly!