THYSANOPTERA.
The very small black flies which are such a source of annoyance to travellers in the summer-time, and which fly into our eyes and crawl over our faces during the prevalence of warm windy weather, principally belong to a kind of insect which is characterised by having very remarkable wings when in the adult condition. These insects exist by myriads, and there are several species of them; and they are all exceedingly destructive to flowers, and especially to the bloom of cereal plants. The little black insects are to be seen on almost every flower, and they devour the delicate cellular tissues of the petals. Thrips cerealium is very destructive when it occurs in multitudes upon the wheat, barley, and oats, for it interferes with the proper nutrition of the grain, by nibbling the protecting envelopes and the tissue which connects it to the stalk.
Figs. 381, 382.—The Adult Insect and Larva of Thrips cerealium (magnified).
All the members of the genus Thrips—and they alone constitute the order now under consideration—possess four very narrow membranous wings, without any folds or network upon them, but furnished and decorated with beautiful fringes upon the edges. These fringes characterise the Order, which in other respects is closely allied to the Orthoptera, and they give the name to it. The Thysanoptera ([Greek: thysanoi], fringes; [Greek: pteron], a wing) have filiform antennæ and very large eyes, and the different species of the genus Thrips have a great diversity of wing fringing. The structure of the wings is somewhat analogous to that observed in the Lepidoptera, in the Pterophorina and the Alucitina.
The metamorphoses of the Thysanoptera have not received much attention, but they are known to be of the incomplete kind. The quiet chrysalis condition is not observed, and the larvæ are born from the egg greatly resembling the adults. The absence of wings is the great distinction between the larval and the imago state, as it is in the closely-allied order of the Orthoptera. The larva moults several times, and the wings are gradually added, the colour of the insect altering also.