Bugs, Cicadas, Aphids, and Scale-insects 
221 
to be expanded by becoming suddenly filled with blood, and contracted 
by a receding of the blood. 
The eggs are laid either under bark or on the surface of leaves or, in 
the case of certain species which have a sharp little ovipositor, underneath 
the leaf-epidermis. They hatch in from three to fifteen days, varying with the 
different species observed, and the young grow and feed for from five to 
forty days. Then follows the brief, quiet, non-feeding stage, and the insect 
becomes mature. Probably several generations appear in a year. The 
winter is passed in either larval, pupal, or adult stage, under bark, in dry, 
hollow plant-stems, in lichens or moss, or on the ground under fallen leaves. 
A curious variation in the adults of many species has been noted in reference 
to the wings; adult individuals of a single species may have either fully 
developed wings, very short functionless wings, or even none at all; both 
sexes may be winged, or one winged and the other not; one or both sexes 
may be short-winged or both be wingless. There seems to exist a condi¬ 
tion somewhat like that in the plant-lice (Aphididae), wings being developed 
in accordance with special needs or influences, as scarcity of food, time of 
the year, etc. 
Another peculiarity of the adults is the rarity, and even, apparently, 
the total lack of males in some species. Parthenogenetic development (the 
production of young from unfertilized eggs) is very common throughout 
the order. 
While the food of those thrips most easily found by the beginning student 
is the sap taken from flower parts, most of the sap-drinking species get their 
supply from the leaves of various plants, and when these plants happen to 
be cultivated ones of field or garden, and the thrips are abundant, these 
tiny insects get the ugly name of “pests.” Three species in particular are 
recognized by economic entomologists as pests, viz., the onion-thrips 
(Thrips tabaci ), the wheat-thrips (Euthrips tritici), and the grass-thrips 
(Anaphothrips striatus). The first of these is about "2T inch long, about 
one-fourth as wide as long, and of a uniformly light-yellowish to brownish- 
yellow color. It feeds on many different cultivated plants, as apple, aster, 
blue grass, melons, clover, tobacco, tomato, cauliflower, etc., etc., but its 
chief injuries seem to be to onions and cabbages. It occurs all over Europe, 
England, and the United States, and is probably the most injurious species 
in the order. The wheat-thrips, also but -fa inch long, brownish yellow 
with orange-tinged thorax, attacks many plants besides wheat, and is very 
fond of puncturing the pistils and stamens of strawberry-flowers, thus often 
preventing fertilization and consequent development of fruit. The life- 
cycle of this species is very short, requiring only twelve days. Eggs depos¬ 
ited in the tissues of infested plants hatch in three days, the larvae are full- 
