These midges, especially in spring or autumn, are often seen in immense swarms arising like smoke over swamps and producing a humming noise which can be heard for a considerable distance. At these seasons they are frequently to be found upon the windows of dwellings, where they are often mistaken for mosquitoes. The larvæ are worm-like, but vary somewhat in form in the different genera. Most of them are aquatic, but a few live in the earth, in manure, decaying wood, under bark, or in the sap of trees, especially in the sap which collects in wounds. [Illustration: 77. Culicoides guttipennis; (_a_) adult, (×15); (_b_) head of same; (_c_) larva; (_d_) head; (_e_) pupa. After Pratt.] Of the many species of CHIRONOMIDÆ, (over eight hundred known), the vast majority are inoffensive. The sub-family Ceratopogoninæ, however, forms an exception, for some of the members of this group, known as sandflies, or punkies, suck blood and are particularly troublesome in the mountains, along streams, and at the seashore. Most of these have been classed under the genus _Ceratopogon_, but the group has been broken up into a number of genera and _Ceratopogon_, in the strict sense, is not known to contain any species which sucks the blood of vertebrates. THE CERATOPOGONINÆ--The Ceratopogoninæ are among the smallest of the Diptera, many of them being hardly a millimeter long and some not even so large. They are Chironomidæ in which the thorax is not prolonged over the head. The antennæ are filiform with fourteen (rarely thirteen) segments in both sexes, those of the male being brush-like. The basal segment is enlarged, the last segment never longer than the two preceding combined, while the last five are sub-equal to, or longer than the preceding segment. The legs are relatively stouter than in the other Chironomidæ. The following three genera of this subfamily are best known as blood suckers in this country.