Among the river sallows, borne aloft
Or sinking as the light wind lives or dies.
(John Keats, To Autumn.)
The female imago hibernates. Finsch made observations and found it hibernating on the frozen Siberian tundras, beneath the moss and snow. Sterling found them in North America when the snow was melting, in great numbers, and he and his party were subsequently terribly bitten. There is no doubt that female imagines live throughout the winter, and they can be found in England, hibernating in cellars, old out-houses, chicken-houses, or disused farm buildings. These hibernating females disappear early in May, presumably having laid their eggs. Dr. Thayer of Baltimore describes these creatures, having found them on the roofs and walls of barns near New Orleans. Whether the male also hibernates is doubtful. Grassi says he never found the male of A. maculipennis in the winter, only fertilised females. But as the warm weather sets in the female generally becomes active and bites, and the native American Indians consider these elderly and famished females give more annoyance than at any other stage in the life-cycle of either sex. In the warmer climate of Southern Italy they not infrequently hibernate in grottos and caves. At times they occur in such numbers that they can be swept up. After depositing their eggs the hibernating females probably die. This usually happens in May.
In the old days we used to collect gnats, keep them in a receptacle unprovided with any food, and when, after a couple of days, they died of starvation we wrote poems or essays on the ‘Transitoriness of Life’ and the ‘Evanescence of Time.’
The thin-winged gnats their transient time employ,
Reeling through sunbeams in a dance of joy.
(Mrs. Norton.)
Nowadays, we feed them. Bananas, sweetened milk, pineapple, or almost any other vegetable juice, is their diet, and in captivity they will live for weeks. At Cambridge in 1900 (July to August), Professor Nuttall was successful in keeping females alive on a diet of bananas and water from two to eight weeks, but it was found essential to keep the atmosphere fairly moist and the food fresh. Grassi found that he could only keep Anopheles alive in his laboratory in Rome for a month.
Both Anopheles and Culex—at any rate, in captivity—lay their eggs early in the morning. Apparently the nature of the food has some effect upon their fertility, certain observers stating that when male and female are fed on vegetable food alone there is no fertilisation and no oviposition. A diet of blood evidently assists the female to lay her eggs, and perhaps to get them fertilised. One of our female Anopheles laid a batch of 146 eggs, and subsequently laid six more. But, as a rule, a fertilised female does not lay a second batch unless she receives a second meal of blood. The eggs are laid two or three days after the meal. There is also some evidence that a meal of blood is necessary if fertilisation is to be effected. As Austen says in The Report of the Sierra Leone Expedition of the Liverpool School of Tropical Medicine:—