When you say "blood", do you mean a red substance? I'm asking because insects don't have blood- they have haemolymph which doesn't contain hemoglobin and is not coloured red (it's actually bluish). If the colour of the substance on your car was red, it was probably human blood from mosquitoes.

Those little flying bastards are plentiful in southern Europe and they can get real fat on human blood and make a surprisingly bloody mess when splatted. They would definitely leave a mark on a white car if it hit them.