262 TRANSACTIONS OF THE HORTICULTURAL 



histories. The plant mites of wliich we write are the smallest of 

 the animal pests with Avhich the horticulturist has to deal. The 

 familiar red spiders, so-called, are the largest examples of the order 

 known to injure plants. But they often appear in great numhers, 

 and this, together with their minute size, makes them difficult to 

 combat. A few notes on their characteristics as animals, and some 

 others on their injuries and the best remedies therefor, may be ap- 

 propriately presented to a body of horticulturists. 



The order constituted by the various species of mites is charac- 

 terized, not so much by the peculiarities possessed by its members, as 

 by their lack of the essential characters of their nearest relatives, 

 the spiders. Mites may, or may not, have a system of air tubes for 

 respiration. Simple eyes may be present or absent. The legs in 

 adults are as a rule eight, and in the young only six legs are present. 

 Mouth parts are present, except in some rare cases. The young are 

 either hatched from eggs, or may be born alive (in which case the 

 mites are ovoviviparoiis, not viviparous^ as stated by Claus). They 

 do not possess a heart. The abdomen is unsegmented, and the head 

 and thorax together form a cephalothorax, which is continuous with 

 the abdomen. 



Three families of the fifteen or more recognized by the author- 

 ities, live upon plants. They are: (T) The Spinning Mites, Tet- 

 mnycliidcB; (II) The Torsowem/c^rt^ a family established for recently 

 discovered forms, not yet designated by a common name, and (III) 

 The Gall Mites, Phytoptida\ The characters given below will serve 

 to distinguish members of the three different families: 



I. Spinning Mites (Tetranychid(r). Legs of six segments, feet 

 with two claws, and also supplied with long, adhesive hairs. Palpi 

 forcipate. Ocelli and tracheae present. Oviparous. Capable of 

 spinning a fine silken thread, with which they cover the leaves. 



II. Tarsonemidft'. Three front pairs of legs with five seg- 

 ments and terminating with two claws and a disc or plantula. 

 Fourth pair of legs, in the male with four, in the female with two 

 segments. Palpi simple and minute. No ocelli. Tracheae present. 

 Female with two peculiar sense-knobs, mounted on i^talks. Integu- 

 ment of the back divided into six plates, giving an appearance of a 

 segmented body. Oviparous. 



ITT. Gall Mites. ( Phytoptidce). With but two pairs of legs 

 each, with five segments and a terminal knobbed claw and spine 

 with prongs. Mouth parts fused into a sucking rostrum, which in- 

 cludes a pair of slender maxillae. No ocelli nor tracheae. Abdomen 

 long, striated transversely, and terminating in a protractile sucker. 

 Oviparous. 



INJURIES BY RED SPIDERS. 



In hot houses, and during dry seasons out of doors also, these 

 mites are often very destructive. The mites are small as compared 



