Hemipterous insects are divided into two groups. True bugs, called _Hemiptera heteroptera_, having the wing-covers opaque at the base, and laid horizontally, and crossing each other obliquely at the end, overlapping; and the Harvest-flies, such as Plant-lice and Bark-lice. These, the _Hemiptera homoptera_, have the wing-covers of one texture throughout, not horizontal, but more or less sloping, and not crossing one another behind. Among these, which all feed upon plants, some very troublesome pests will here be noticed. =COCCIDIANS.=--BARK-LICE. =Aspidiotus conchiformis=, or the Apple Bark-louse, is very numerous in many parts of our country, particularly north of latitude 40 degrees. It commits sad devastations in some sections. Individually, it is but a little scale; but these animals are wonderfully prolific and soon cover every twig of the tree, obstructing its transpirations, and abstracting its vital juices; the leaves, and even the fruit are overrun with these miserable scales, but the twigs are their favorite resort. These scales are oblong, shaped like an oyster shell; flat and brown, often crowding upon one another. In the winter and spring, they contain or cover a number of small, round, white eggs, which hatch out in the spring, in May, attach themselves to the bark, and absorb the juices: various remedies have been suggested, and more or less thoroughly tested. The restoration of the thrifty growth of the tree is considered essential to success; and without this, all remedies are looked upon as unavailing. Some orchardists think that thorough drainage and cultivation of the land would alone banish the lice, but this can hardly be hoped. Strong lye, or solutions of potash, or soda, white-wash, and sulphur, have been used, and tobacco boiled in lye, soft-soap and tar mixed with linseed oil, which makes a kind of varnish. Mr. Walsh tells us that applications, to destroy this insect, are better made in May or June, as the eggs are protected by the scale in winter, and it is impermeable to watery solutions. This pest has been imported from Europe. Walsh recommends the use of Lady-birds to check the Bark-lice.[25] =Lecanium pyri=, (_Fitch_), or the Pear Bark-louse, is a hemispherical brown scale, as large as a split pea. They may be found in summer on the under side of the limbs, and are the remains of dead females, which cover the eggs and young brood. This insect would be very injurious, were it to increase in numbers considerably. Let young trees be examined in June, when the scales may easily be found, removed, and destroyed. =Lecanium persici=, or the Peach Bark-louse, is described, by Fitch, as similar in size to the above, found on smooth bark near a bud; it is blackish, uneven, shining, with a pale margin.