PARASITISM 317 



its eggs in the tomato worm and other Sphin- 

 gidae; the little cocoons which the caterpillar 

 carries fastened to its back giving its body 

 the appearance of being covered with rice 

 grains. 



Many species are provided with remarkably long 

 ovipositors with which to reach the larvae, 

 which may lie hidden away under bark, in bur- 

 rows in wood, in tunnels in the earth, or with 

 which they bore through cocoons to reach the 

 insect hosts at the beginning of the stage of 

 pupation. 



Some of these insects (Thallissa lunator and 

 Pimpla) are large and robust, measuring 

 8 to 10 cm., and provided with ovipositors, 

 20 cm. or more in length; others, the Procto- 

 trypidaB, are so tiny as to be enumerated among 

 the smallest known insects. Such minute 

 insects oviposit in the eggs of other insects and 

 of spiders. 



The hymenopterous parasites are of immense 

 benefit to man by holding in check his chief 

 insect enemies, especially coleopterous and 

 lepidopterous insects. For the destruction 

 of the cotton worm and the Hessian fly, we 

 are entirely under obligations to them. 

 It is interesting to observe in conclusion that 

 the parasitic habit is so largely developed among 

 the hymenoptera that super-parasites i.e., 

 parasites of parasites may reach even the 

 third and fourth degree. 



Class Arachnida. Of this class which in- 

 cludes the ticks and mites, the scorpions and 

 spiders, we find practically all of the ticks and 

 one-half of the mites to be parasitic, either 

 upon animals or upon plants. 

 The ticks comprise two families, the Argasidae 

 and the Ixodidse which form the superfamily 



