The square-spot deerfly (Chrysops viduatus) is a horsefly. That might seem like a contradiction of terms but let me explain. The familiar name of horsefly is given to the insect family with the scientific name of tabanidae and, in general, the female of this family of flies depend on acquiring blood from mammals to enable her eggs to develop. They mainly attack horses for this blood supply but Chrysops viduatus is an exception and attacks deer. So, this horsefly is a deerfly.
Horseflies are not usually known for their good looks but I think this particulat species, albeit a deerfly, is quite an attractive insect with striking colours and lovely blue eyes! Before you think I am nuts remember that beauty is in the eye of the beholder and I happen to think there is beauty in many species that other people do not.
This species is widespread in south eastern England and can be found in meadows and woodlands where there are deer present. They are not common but can be frequent where a deer population exists. I believe any species of deer will do but I suspect roe deer are its main source of blood.Chrysops viduatus: the square-spot deerfly