The Dark Fly
The dark fly, Anopheles caligatus, does not get its name from its color, which is, in fact, a light grey. Rather, it is due to its preferred habitat. Just as the dark fly is not a fly, but a mosquito.
The dark fly lives mainly in the caves of Southern Europe, although some colonies have been found as far north as Bergen, in Norway, and others as far south as the Atlas mountains in Morocco. Although many mosquito species fly in swarms during the mating season to improve chances of reproduction and as a defense mechanism against predators, the behavior is more pronounced in dark flies, and for good (evolutionary) reasons.
Living in caves, they often share their habitat with bats. Dark flies emit a strong odour that repels the nightly mammals, but only if they can gather in big enough swarms for the smell to reach a certain threshold. Otherwise, the bats will trade off the slight dipleasure for a juicy meal. However, it has been observed on mutlitple occasions that, whenever a swarm of dark flies manages to settle in a cave, it will soon drive out the bats. Indeed, Dr. Hugo Forsher, from the German Institute of Reverse Displacement (DIVV, Deutsches Institut der Verkehrten Verscheuchung), believes that dark flies are one of the main causes for dwindling bat populations in Europe today.
The fact that dark flies ar drawn to darkness, and not light, is an as-of-yet unexplained curiosity. This behavior has driven the mosquitoes into caves, where the low visibility and intense echoes make communications through sound and sight impractical. Because of this, dark flies have a very pronounced olfactive sense. It is believed that there is not a place in Europe from where a dark fly would not be able to find the nearest colony of its fellows.
Although they rarely come into contact with humans due to their living preferences, a few cases have been reported where people venturing into caves inhabited by dark flies have had so much of their blood sucked that their lives where in jeopardy. What the mosquitoes eat when no humans are present is not yet know, altough scientists believe their diet must consist mainly of small mammals that wander into their territory. None of them went to check, though.