Culicoides are small, midget-like nematocera flies (about 1-3 mm) with an elongated body. They are most active at sunset, especially between 7 p.m. and 10 p.m., but some species are also known to bite during the morning, while others seem to be nocturnal. The duration of these insects’ biological cycle sensibly varies from one species to the other according to region, climate and season.
In Italy, they can be seen from March to the end of September but they are particularly numerous during spring and early summer. Larvae preferably develop in mud or highly damp places, such as rivers, small stretches of stagnant or low-flowing water, brackish environments and dunghills, when the external temperature is above 10°.
The damage caused to the horse’s skin by these insects’ bites is quite severe. Indeed, Culicoides’ big proboscises prevent them from directly reaching capillaries, as mosquitos do. Therefore, these insects cause a small haemorrhage of blood from which they feed (telmophagy).
Not only Culicoides’ bites are annoying and make horses spontaneously look for cover, but they also cause wounds that often lead to bacterial and viral infections: indeed, lab analyses show that over 50 different viruses are transmitted by Culicoides.
During the summer, horses affected by sweet itch are more nervous, anxious and often refuse to be ridden. Moreover, they are so distressed by the itch that they eat less and, therefore, may loose from 10 to 15% of their bodyweight.