36 



Until within the year 1900 the common red spicier most of ten occur- 

 ring in greenhouses was technicall}^ designated as Tett'anychus telarlus 

 Linn., a name wliich has been rather indiscriminately applied to all 

 species of red spiders, both in America and abroad. 



Red spiders are not true insects, in fact not even spiders, but are, 

 more properly speaking, spinning mites. Since, however, thej'' are 

 almost universally known as red spiders, this term is retained for 

 present purposes. 



As the word ""mite'' indicates, these insects are extremely minute, 

 and when they occur in ordinary numbers are not apt to be noticed 

 unless leaves are carefully scrutinized. Attention, however, is certain 

 to be drawn to them when they become excessively numerous, as fre- 

 quently happens in neglected greenhouses 

 or out of doors during droughts in sum- 

 mer. 



Red spiders spin threads, but do not, 

 like true spiders, utilize them for climb- 

 ing or descending from a height. The 

 threads spun are extremely fine and 

 scarcely perceptible to the unaided eye, 

 but a web of threads is frequently so dense 

 as to form a tissue plainly visible at a little 

 distance. Webs are usually constructed 



Fig. y. — Tctranychas bimaculatus: 

 adult— enlarged (from Banks). 



Fig. 10. — Tetraiiy- 

 ckus bimaculatu.t: 

 palpus — enlarged 

 (from Banks). 



¥ iG. II. —Tetrany- 

 chus bimacula- 

 tus: claw.s — en- 

 larged (from 



Banks). 



upon the lower sides of leaves, and attached here and there to project- 

 ing hairs, veins, or the edges of the leaves. Within the weljs thus 

 formed the mites feed in their different stages, and the eggs are laid 

 from which the young develop. 



The general appearance of the red spider under consideration, which 

 is now known as Tefmni/chns hiuiaculatus Ilarv. as it looked under a 

 microscope, is well shown in iigure 9. At liguro 10 a greatly enlarged 

 palpus of the same species is illustrated, and figure 11 shows the claws 

 similarly enlarged. 



The length of full-grown individuals, including the palpus, is from 

 0.4 to 0.6 """ and the width 0.25 to 0.80 '"'", the thickness being 0.17 



