I would guess that most people in the southern half of France have seen and jumped away from this great green eyed fly. It seems to be that known as Philipomyia graeca. The scrap of doubt is there because there are many species of horse flies (French - taon). All have evil reputations. A bite can produce in man swellings the size of an apple. Most have favourite species of mammal on which to take their meals, but humans are too often a nice diversion. It is only the the females which bite, which they do after mating. The blood meal seems to be necessary for producing the eggs. During June I must have captured about thirty on the inside of the house windows. All of them were females and only one appeared to show any interest in biting me. I have yet to capture a male. The specimen illustrated is therefore a female. How do I know? Observe the eyes. They do not quite touch each other. There is a gap. If it were a male the two eyes would touch. In front of and slightly below the eyes are the two short antennae. The proboscis is between these. Its structure is partly obscured by two cream coloured palps lying close together. In the males these palps are short. Where then are the males? Possibly they are out in the woods or fields circling about under overhanging branches waiting for a female to arrive. They possibly get some nutriment from the nectar of broad flat flowers like the hogweeds. All these comments are guesswork. One supposes that the behaviour of the sexes are different. The females seek some dark place (the blackness of an open door) and then - it seems stupidly - seek the light again. If the males stay in the open, then how does this help them find a mate?
My authoritative reference book on the Horse Flies of Europe says that nothing whatsoever is known of the life cycle of Philipomyia; where it lays its eggs, where the maggots live, where they mate, what is the favoured prey. The blood prey is likely to be sheep, or wild deer, our most common large mammals. The maggots probably live in damp leaf litter, eating other small larvae.
Many horse flies have eyes with astonishing colours. Sometimes they are barred in red and green. These colours completely fade away in death, leaving a dull brown. One assumes that the colours are a consequence of the refraction of light on the eye and are not due to any chemical constituents. Again, one can conjecture what advantage is it to have these colours? I doubt if it is to scare the human victims.
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