THE HARVEST MITES. 181 



attack; whilst others do not disdain dead, and even dried animal and vegetable materials, and thus 

 act the beneficial part of scavengers. In a fossil state Acariiia are known only as inclusions in 

 amber. 



The Acarina may be divided into seven great families, some of which, however, include a 

 considerable variety of forms. The following tabular arrangement will serve as a guide to their 

 general characters : 



I. Fore part of head prolonged into a distinct beak, and separated by a constriction from the 



rest of the body .......,, 1. BDELLIDJE. 



II. Fore part of head not prolonged into a distinct beak. 



A. Skin firm. 



1 . Skin scarcely extensible ; palpi not seated on a common chin-piece. 



a. Chelioerse claw or needle-like. 



* Palpi terminated by a pair of nippers . 2. TROMBIDIIDJE. 

 f Palpi with bristles or a hook at the extremity . . , 3. HYDKACHNIDJE. 



b. Chelicerse with nippers. 



* First joint of palpi very large ..... 4. ORIBATIDJE. 

 t Joints of palpi nearly equal ..... 5. GAMASID^E. 



2. Skin leathery, very extensible ; palpi attached to a chin-plate . . 6. IXODIDJE. 



B. Skin soft, with a few chitinous bands ..... 7. ACARID.E. 



FAMILY I. BDELLIDJE, OR BEAKED MITES. 



In these there appears to be a distinct head, separated by a constriction usually resembling a 

 short neck from the rest of the body, but this projecting beak apparently consists only of the mouth, 

 and the eyes, when present, are situated behind the constriction. The latter organs vary in number 

 from two to six. The chelicerse terminate in nippers ; and the first pair of palpi are long and slender, 

 composed of five joints, and generally more or less elbowed at the end of the second joint. These are 

 small Mites, usually of a bright colour, slow in motion, and living in damp ground. The young 

 resemble their parents. The best-known species is JBdella longicornis, which is about one twenty-fourth 

 of an inch long, scarlet, with four eyes. These Mites appear to be predaceous in their habits. 



FAMILY II. TROMBIDinXE, OR HARVEST MITES. 



This is a much more extensive family than the last, with which, however, it has much in 

 common. Its members never display the separate head-like part characteristic of the Bdellidae, and 

 the first palpi are short and stout, but their termination shows two opposite pieces, one of which is a 

 claw. The chelicerse do not end in nippers ; and the legs consist of six or seven joints, and are 

 terminated by a pair of claws. These Mites are generally of some shade of red, often of the brightest 

 vermilion, but sometimes more or less spotted with brown or black. They live upon the ground, and 

 among plants, and many of them run very fast. The young are six-legged, but otherwise like their 

 parents. Many of them pass through a parasitic stage. 



A considerable number of these Mites are vegetable feeders, and some of them occasionally do 

 a good deal of mischief to various plants and trees, of which they frequent the under sides of the 

 leaves, pricking the tissues with their sharp chelicerse, and sucking out the fluids. One of the 

 commonest species is well known as the Red Spider (Tetranychus telarius), although it varies a good 

 tleal in colour, apparently with age ; but the majority of the specimens are of a brick-red. It is 

 found upon a great variety of plants and trees in our gardens, spinning an exceedingly delicate web, 

 under which a whole colony of all ages lives in security. Other species of the genus Tetranychus 

 and its allies also abound upon many cultivated and wild plants. The young form of one species, 

 which appears to be a Tetranychus, is the well-known " Harvest Bug," which torments tender-skinned 

 people so seriously if they wander in country places in the autumn. The Mite that penetrates the 

 skin is the six-legged form, and has been described under the name of Leptus autumnalis. It attacks 

 not only human beings, but dogs, cats, and many other animals. The best remedy for the itching it 

 produces is to nib the part affected with some essential oil. 



The Scarlet Mite (Trombidium holosericeum) may serve as the type of a large group of Mites 

 belonging to this family, but of carnivorous habits. It is about a twelfth of an inch long, with 



