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.
[Illustration: 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.