In the perfect state, as well as in that of the larva and the pupa, the _Libellulæ_ are carnivorous. Their rapid flight makes them expert hunters, and their enormous eyes embrace the whole horizon. They seize, while on the wing, flies and butterflies, and tear them to pieces immediately with their strong mandibles. Sometimes, the ardour of the chase leading them on far from the streams, they are met with in the fields. The female lays her eggs in the water, from which emerge larvæ which remind one somewhat of the form of the insect, only their body is more compact and their head flattened. The larvæ and pupæ inhabit the bottom of ponds and streams, where, keeping out of sight in the mud, they seek for insects, molluscs, small fish, &c. If any prey passes within their reach, they dart forward, like a spring, a very singular arm, which represents the under lip. It is a sort of animated mask, armed with strong jagged pincers and supported by strong joints, the which, taken together, is equal to the length of the body itself. This mask acts at the same time as a lip and an arm; it seizes the prey on its passage, and conveys it to the mouth. "When any aquatic insect approaches them at a time when they are in a humour for eating," says Charles de Geer, "they shoot the mask forward very suddenly and like a flash of lightning, and seize the insect between their two pincers; then, drawing back the mask, they bring the prey up to their mandibles, and begin to eat it. I have remarked that they do not spare those of their own kind, but that they eat each other up when they can, and I have also seen them devouring very small fish which I put by them. It is very difficult for other insects to avoid their blows, because, walking along generally in the water very gently, and, as it were, with measured steps--almost in the same way a cat does on the look-out for birds--they suddenly dart forward their mask and seize their prey instantaneously."[118] Fig. 394 represents, to the left, the larva of the dragon-fly, with the instrument of attack which we have called a "mask," and which it is making use of for seizing a small insect; on the right, the adult dragon-fly coming out of the nymph. [118] Charles de Geer, "Mémoires pour servir à l'Histoire des Insectes," tome ii., 2e partie, p. 674. [Illustration: Fig. 394.--Larva of the _Libellula_, and the perfect insect emerging.] [Illustration: Fig. 395.--Libellula depressa, the Common Dragon-Fly.]