The following law is likely to hold good for the Culicidae which feed on man—at least for the common species; although these gnats can live indefinitely on fruit, the female requires a meal of blood both for fertilisation and for the development of the ova. In other words, the insects need blood for the propagation of their species.
Undoubtedly, if mosquitos ever talk, they would talk like Mr. Waterbrook, Mrs. Henry Spiker—Hamlet’s aunt—and the ‘simpering fellow with weak legs’ talked when David Copperfield dined with the first-named at Ely Place, Holborn. The burden of their song was: ‘Give us blood.’
But a word of caution must be given here. Most of these deductions are based upon mosquitos in captivity; whether the same be true of them in natural conditions is not quite certain. If it be so it is difficult to see how these countless millions of gnats and mosquitos which dwell in the barren regions around the polar circle ever keep going.
It very frequently happens in the Animal Kingdom that females are much more numerous, as well as much larger, than the males.[5] As Kipling tells us: ‘The female of the species is more deadly than the male,’ but Professor Nuttall and I did not notice that this was the case with Anopheles.
There is some evidence that the male hatches out earlier than the female, and that in Southern Europe there may be three or four generations in the course of the season: the first beginning in April and the fourth taking place between the middle of September and the middle of October. After that date no larvae were found. About four generations also occurred in the neighbourhood of Cambridge, according to observations of Professor Nuttall.
Kerschbaumer has calculated that if the average number of eggs laid by a female be 150, the number of the descendants by the fourth generation would amount to 31 millions. This readily accounts for the fact that in certain parts of the world they occur in perfectly enormous numbers, and if it be true that blood is essential for fertilisation and oviposition, very few of these potential mothers can breed. In nature they will feed on a great number of vegetable juices—melons, wild cherry-blossom, bananas, oranges, overripe mangoes; they suck the ‘juices’ of allied species of insects just when the imago is issuing from the pupa-case and before their integument is hardened, or they pierce the soft skin of the cicada, and occasionally attack the chrysalids of a butterfly. One of the most curious sources of food are very young trout. The adult insect attacks these petits poissons filiformes, ‘literally sucking out their unsuspective little brains before they could escape.’ Grassi is doubtful whether the adult males feed at all. He states that he never found any food in their stomach, nor has he ever seen a male feed. But Professor Nuttall’s experiments in Cambridge prove that males were seen repeatedly to feed, and to feed hungrily, on cherries, dried fruits, dates, and bananas.[6]
Fig. 16.—View of my arm being sucked by Anopheles maculipennis (female). (From Nuttall and Shipley.)
As mentioned before, the proboscis of the male is too weak to pierce the human integument, but Howard notes that it will suck up water, molasses, and beer; and Gray, at Santa Lucia, mentions that in that island Culex had developed a marked fondness for port wine. One particularly favourite food is rose-buds covered with aphides—probably due to the sweetened secretion which these insects exude. The feeding is sometimes very ravenous, so that the insects become distended, the bright colour of blood, or coloured sap, readily shining through the joints of their chitinous armour.
The reaction to heat and cold is that common to many insects. During the winter the imagines become torpid, quiescent, and cease to worry one. With returning warmth they become lively again, and generally wake from their winter sleep in a state of considerable hunger. They are insects which prefer darkness to light, and during the day-time congregate in caverns and grottos, under the shade of trees and bushes, beneath bridges, in barns, and so on. As the sun sinks they emerge from their hiding-places and fly during the night.