BULLETIN 39, UNITED STATES NATIONAL MUSEUM. [128] 



figure, Notlirus ovivorus lias been observed by Dr. Packard to eat the 

 €ggs of the Canker Worm. 



The members of the family Gamasidie are parasitic upon animals, 

 but chiefly upon insects. The Hydrachnidse are parasitic also upon the 

 aquatic insects, and also affect fish or mussels or 

 occur on fresh-water j^lants. 



One of the most imjDortant families of mites is 

 the Trombidiidise which includes a large number 

 of species, some of which occur in immense num- 

 bers. Most of them are vegetable feeders, but 

 some species feed on the eggs of insects. 



The genus Trombidium includes a number of 

 the Eed Mites which feed on insects in all their 

 stages. The Locust Mite, Trombidium locustarum 

 Eiley, is one of the most interesting as well as one 

 of the most important of our locust enemies, and will serve to illustrate 

 the habits of the group. It differs so much in infancy and maturity that 

 it has been referred to different genera and is known under different 

 names. The mature form lives on the ground and feeds on all sorts of 

 animal or decomposing vegetable matter, and wherever the gTound is 

 filled with locust eggs these afford an abundance of food and the mites 

 flourish and multiply rapidly. In the spring the female lays 300 or 400 



Fig. Ii5. —Nothrus ovivorus 

 Packard. 



Fig. \ZQ.—Iromhidium locustarum: a, female with her batch of eggs; 6, newly hatched larvar— 

 natural size indicated by the dot within the circle; c, egg; d e, vacated egg-shells. 



minute spherical orange-red eggs in the ground (Fig. 136«). From 

 these eggs, as shown enlarged at c, d, and e (the two latter being the 

 vacated egg shells) emerge the six-legged larva shown at h. These are 

 mere specks and crawl actively about, fastening themselves to the 

 locusts mostly at the base of the wings or along the upper veins. 

 They subsist on the juices of their host. They firmly attach themselves 

 by the mouth and increase rapidly in size, the legs not growing and 

 becoming mere rudiments. In this form they are shown at Fig. 137a. 

 When fully developed they let go their hold, drop to the ground, and 



