When _Psithyrus_ is present in a nest of _Bombus_ it apparently affects the inhabitants only by diminishing their stores of food to so great an extent that the colony remains small instead of largely increasing in numbers. Although _Bombus variabilis_, when left to itself, increases the number of individuals in a colony to 200 or more, Hoffer found in a nest in which _Psithyrus_ was present, that on the 1st of September the assemblage consisted only of a queen _Bombus_ and fifteen workers, together with eighteen specimens of the _Psithyrus_, eight of these being females. The nests of _Bombus_ are destroyed by several animals, probably for the sake of the honey contained in the pots; various kinds of small mammals, such as mice, the weasel, and even the fox, are known to destroy them; and quite a fauna of Insects may be found in them; the relations of these to their hosts are very little known, but some undoubtedly destroy the bees' larvae, as in the case of _Meloe_, _Mutilla_ and _Conops_. Birds do not as a rule attack these bees, though the bee-eater, _Merops apiaster_, has been known to feed on them very heavily. The genera of social bees known as _Melipona_, _Trigona_ or _Tetragona_, may, according to recent authorities, be all included in one genus, _Melipona_. Some of these Insects are amongst the smallest of bees, so that one, or more, species go by the name of "Mosquito-bees." The species appear to be numerous, and occur in most of the tropical parts of the continents of the world, but unfortunately very little is known as to their life-histories or economics; they are said to form communities consisting at times of a countless number of individuals; but it has not been thoroughly ascertained whether these are the produce of a single queen, as in the case of the hive-bee, or whether there may be more than one egg-producer in each community. The late F. Smith thought the former of these alternatives would prove to be correct. These mosquito-bees are frequently spoken of as stingless bees, but this is not quite correct, for although they do not sting, {62}von Ihering[34] says that all the essential elements of the sting are present, the pointed or penetrating part of the apparatus being stunted. It would serve no useful purpose to attempt to construct the social history of these stingless bees from the numerous brief scattered accounts in entomological literature, for they refer to different species; it is, however, positively stated by Smith on the authority of Peckolt[35] that _Trigona mosquito_ sends off swarms after the manner of the hive-bee in this country, and that after searching six hives only one royal female could be found in each. [Illustration: Fig. 24.—_Melipona_ sp. ♀. Amazons.]