Photo by W. P. Dando, F.Z.S., Regent's Park.
SCALE-INSECT.
The females die, covering their eggs with their own bodies.
Photo by W. P. Dando, F.Z.S., Regent's Park.
SCALE-INSECTS.
Showing their appearance when crowded together on a branch.
Many of the Aphides exhibit the curious phenomenon known as "alternation of generations." The first brood consists of winged males and females; but the eggs which the latter lay produce exclusively wingless females, or rather sexless creatures capable of laying eggs, and these multiply indefinitely for a time, till perfect males and females are again reproduced. In some cases the winged forms live on the leaves of trees, and the wingless forms at the roots of grass, etc. One of the most destructive of all these insects is the Vine-aphis, which was probably introduced into Europe from America, and which threatened at one time almost to destroy the vine industry in France. Wingless sexless forms live and multiply at the roots of vines; and in summer winged males and females are produced, which fly up, and lay eggs on the leaves; while some of the wingless insects also quit the ground, and form small galls on the vine-leaves. Although very abundant in America, the insect is not nearly so destructive to the plants which it attacks as in Europe.
Some species of Scale-insects are almost equally destructive, especially to greenhouse plants. The male is slender and two-winged, but the female is wingless and often legless, and after depositing her eggs usually dies above them, thus forming a covering to protect them from injury. Cochineal consists of the bodies of a species of scale-insect which infests the leaves of a cactus in Mexico.
The True Lice are found on various species of mammals, and imbibe their food through a proboscis. The Bird-lice, or Biting-lice, form a well-defined group by themselves. They are sometimes regarded as forming distinct orders of insects; but some authors treat the first group as a degraded family of insects allied to the Frog-hoppers, and the second group as an equally degraded and aberrant family allied to the Lace-winged Insects.