Another group of mites of importance to the horticulturist is that of the blister mites; they are so minute--measuring about a hundred-and-fiftieth of an inch long--as to be invisible to the unaided eye. Though so minute, however, their damage to foliage is characteristic and conspicuous, so that their presence is easily detected. The most important blister mite in New Zealand is the pear-leaf blister mite (_Eriophyes pyri_); it differs from the other mites described above in having a long and cylindrical body, with only two pairs of legs crowded at the head end, the elongate abdomen having the appearance of being composed of innumerable segments (Fig. 13, 11). This mite lives in colonies in blisters formed on the leaf, and sometimes on the leaf petioles. In the spring the yellowish-green blisters will give the upper surface of an infested leaf a spotted appearance, and as the season advances these blisters become reddish and finally brown; in the case of severe infestation, the blisters become so crowded as to merge into masses. During the winter the mites lie in the shelter of the bud scales; as soon as the foliage begins to develop in the spring the over-wintering mites attack the leaves, each mite forming a blister, in which it produces a colony of young. The offspring then migrate from the parent blister and form blisters for themselves, and this goes on until autumn, when the last generation of mites migrates for the winter to the shelter of the bud scales. Owing to the mites being protected within the leaf blisters, summer sprays are not effective as a means of control, which can be effected, however, by spraying with lime-sulphur in the autumn, when the mites are taking up their winter quarters, and again at bud movement in the spring. Woodlice. Woodlice are so well known, that but little description is necessary here. However, the following features are of interest. They belong to the group of animals known as the _Crustacea_, which also includes the crabs; these animals breathe by means of gills, and are usually aquatic, but some forms, such as the woodlice, have become adapted to a life on land. In outline (Fig. 13, 12) the woodlice are more or less oval, with the upper surfaces somewhat arched, and the lower flat; the body is divided into several segments, which may enable the animals to curl up in the form of a pill. There is a distinct head, bearing a pair of antennæ and the mouth-parts, followed by seven large thoracic segments, to each of which a pair of legs is attached; finally, the remaining six segments are more or less crowded together, and constitute the abdomen. Since woodlice are terrestrial gill-breathing animals, moisture is essential for them, and it is in moist places that they abound. They depend upon a mixed diet, being carnivorous, as well as herbivorous; though normally scavengers, their attacks upon seedlings and tender parts of plants bring them into the ranks of important garden pests.