Читать книгу Extreme Insects - Richard Jones - Страница 30

NAME	big-headed flies in the family Pipunculidae
LOCATION	worldwide
ATTRIBUTE	superb stock-still hovering

When, on 29 September 1907, the French aviation pioneer Louis Charles Breguet lifted off the ground in an erratic prototype helicopter, Gyroplane 1, he was trying to emulate a flight technique long mastered by insects – hovering. The ability to hang in mid-air, even for just a moment, is of paramount importance if an insect wants to land on a leaf or a flower, as there are no runways for a glide-down descent.

Because insects can flex (twist) their wings, thrust and lift can be generated by both backwards and forwards strokes. In the fastest insects, the power stroke (pushing backwards) and the recovery stroke (pulling the wings forwards again) generate nearly all thrust, with just enough lift to keep level flight. In hoverers, thrust and lift are directed straight down, with just enough power to support an insect stationary.

Among the best-known hovering insects are the hawkmoths and bee-flies, which hover apparently motionless while drinking nectar from a flower. Others include the hoverflies, named for their habit of hovering in a shaft of light, over a flower, or in a woodland clearing. That hovering is important to these large and brightly coloured insects is demonstrated by the fact that they have huge eyes; in the males there is very little else on the head except the eyes. The large eyes give all-round vision to monitor the air-space in every direction and to maintain a fixed hovering point in the air. The males have larger eyes as it is they that do most of the hovering, guarding a three-dimensional territory, seeing off other males and enticing females.

But even hoverflies are out-hovered by one other group of insects, which are rather small and drab. The obviously named big-headed flies have big heads and, again, the males are all eyes. Their vast eyes give the same clue to all-round vision and territoriality. But instead of hovering brazenly in the large air-space under the spreading bough of a tree, they choose a discrete bush or a small space within the herbage. To the entomologist they demonstrate their flying skills by hovering in the folds of the insect net or inside the small glass tube as they are examined under a hand lens.