ROSS: HOW TO COLLECT AND PRESERVE INSECTS 



51 



feed on the blood of birds and other animals, have sucking mouth- 

 parts. They are powerful jumpers. The young stages are slender, 

 white worms, which live in the nests of various animals; these 

 larvae are seldom collected. The fleas are found on the animals 

 themselves or around their nests. Several species of fleas, includ- 

 ing the cat and dog flea, the human flea, and the rat fleas, attack 

 man. One of the rat fleas, Xenopsylla cheopis (Rothschild), is 

 of especial importance because it is the common transmitter of 

 bubonic plague. 



RELATIVES OF INSECTS 



There are many small animals that belong to the same 

 general group as insects and that are frequently collected with 

 them. Spiders, centipedes, and amphipods are a few of many 

 examples of such animals. Together with insects they form the 

 animal phylum called Arthropoda, characterized by having seg- 

 mented bodies and jointed legs. A brief description is included 

 here of the commoner groups of these insect relatives found in 

 Illinois. 



Isopoda These animals are convex, many legged, and 



Sow Bugs, have conspicuous antennae ; several of the 



Pill Bugs posterior segments are short and joined 



rather closely to form an abdomen. Of the 

 Illinois forms, about one-half are aquatic, living in streams and 

 ponds. The others live in terrestrial situa- 

 tions that are humid and dark. They are 

 frequently found under boards and in soil 

 in greenhouses. One species of this group 

 is Porcellionides pruinosus (Brandt), fig. 

 56. Many of the terrestrial forms possess 

 the ability to curl up in a hard shell-like 

 ball when disturbed. These animals, rela- 

 tives of crabs, shrimps and crayfish, belong 

 to the general group known as crustaceans. 

 The crustacean groups are abundant in the 

 ocean. In past geologic ages, the early 

 ancestors of such predominantly terres- 

 trial groups as insects and spiders re- 

 sembled ancestors of the present crusta- 

 cean marine forms. 



Fig. 56. — Isopoda. 

 Porcellionides pruino- 

 sus, a common green- 

 house sow bug. Actual 

 length 0.3 inch. 



