Photo by W. P. Dando, F.Z.S.] [Regent's Park.
DRAGON-FLY.
These insects are often known as "Horse-stingers," although they do not sting horses; in fact, they are perfectly harmless, except to insects smaller and weaker than themselves.
The method of swimming practised by the dragon-fly grub is also very curious. Through the centre of the body runs a longitudinal tube, terminating in a circular orifice, closed by means of five tightly fitting valves. These valves, which together form a sharp spike when closed, can be separated at will. When the insect wishes to swim, it fills the tube with water, and then squirts the contents forcibly out, the result being that it is driven swiftly forwards by the reaction.
The pupa of the dragon-fly is very much like the grub, with the exception that the rudiments of the future wings may be seen on the back.
About forty species of these insects are found in the British Islands, of which the Great Dragon-fly is a well-known example. The body is 3 inches in length, while the extended wings measure about 4 inches from tip to tip. In colour it is light rusty brown, with a few pale markings. The "Horse-stinger"—which is perfectly harmless, notwithstanding its popular title—is also common, and may be recognised at once by its flat dull yellow body, which becomes blue in the fully developed male. In the graceful and beautiful Demoiselle the male is deep blue, with black patches on the wings, while the female is entirely green.
Allied to these insects is the Common May-fly, popularly supposed to live for one day only. As a matter of fact, however, it spends a couple of years in the grub and pupa states, inhabiting burrows in the banks of ponds and streams. These burrows are curved, and have two entrances, one above the other, so that the insect can pass in and out with perfect ease.
The May-fly is also remarkable for the fact that the perfect insect changes its skin shortly after reaching maturity. Before this change takes place the female insect is the "Green Drake" of the angler; afterwards, the "Grey Drake."
