Flies are also useful in keeping down the multitudes of destructive insects. Numbers of caterpillars fall victims to the bristly flies alluded to on the last page; and the Bee-flies, which form a family placed next to the Gad-flies, render far greater service in destroying locusts. They much resemble small bumble-bees, being very much the same shape, and they are clothed with yellow down in the British species, and the transparent wings are conspicuously marked with black bands (as in the photograph above), or with brown shading and spots. The insects have a very rapid flight, and use their long proboscis to suck the honey of flowers; but their grubs are parasitic—at least in some instances—on wild bees; and it is probable that their resemblance to bees has some reference to this mode of life. But in Cyprus, Algeria, North America, etc., the larvæ of allied species feed inside the egg-cases of locusts, sometimes destroying as large a proportion as four-fifths of the whole brood. Locusts have many enemies, but it will easily be seen that the attacks of foes like these must reduce their numbers considerably, notwithstanding the swarms which frequently survive, and which are liable to the attacks of other enemies, such as robber-flies, locust-birds, etc., after they have actually arrived at maturity.
Nor must we omit to notice the use of flies as articles of food for man or useful animals. Many persons are very fond of cheese-hoppers, which are really the maggots of a small fly; and we read in Kirby's "Textbook of Entomology," page 92: "The Rev. A. E. Eaton informs me that he believes that two species of Ephemeridæ (May-flies) form a portion of the so-called 'Kungu Cake,' manufactured by the natives of South Africa of gnats, and probably any other insects which can be obtained in sufficient abundance." "Gentles," which are the maggots of flies, are used by anglers for ground-bait.
Photo by W. Saville Kent, F.Z.S. Milford-on-Sea.
PORTION OF INSHORE CORAL REEF AT THURSDAY ISLAND, TORRES STRAITS.
In the foreground are hemispherical masses of the so-called Brain-Stone and Star-Corals. In the background the rocks are encrusted with various species of soft-fleshed corals allied to the similar "Dead Men's Fingers" of the British Seas.
BOOK VI. SHELL-FISH, LAMP-SHELLS, SEA-URCHINS, STAR-FISHES, MOSS-ANIMALS, WORMS, CORALS, JELLY-FISHES, AND SPONGES.
BY W. SAVILLE-KENT, F.L.S., F.Z.S.