36 



ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 39 



usually two pairs of wings, and two or three long tails. When 

 the insect is at rest, the wings are held together above the body. 

 Hexagenia limbata (Guerin), figs. 27 and 28, is one of our very 

 common mayflies and is an important factor in the food economy 

 of many Illinois fish. 



Mayflies, formerly called Plectoptera, together with stoneflies, 

 caddisflies, and midges, constitute a very abundant portion of the 

 life of our lakes and streams, and they are important as fish food. 



Odonata In this order, also, the nymphs develop in 



Dragonflies, streams, lakes, or ponds ; the adults are aerial. 



Damselflies The nymphs have short antennae, long legs, 



and either a stout body with no tail (dragon- 

 fly nymphs) or a slender body with three leaf like gills projecting 

 from the end of the body (damselfly nymphs) . Most distinctive 

 for this order is an extensile "mask," which fits over the face of 

 the nymph and which is hinged to extend forward and seize the 

 small animals upon which the nymph lives. The adults are large, 

 often beautifully colored, as the Libellula luctuosa Burmeister, 

 fig. 29. They have chewing mouthparts and two pairs of large 



Fig. 29. — Odonata. Libellula luctuosa; the adult form of this dragonfly 

 pursuing a fly. Under the water are shown two typical dragonfly nymphs, 

 the lower one with the "mask" outstretched. Actual length of adult about 

 1.5 inches, wingspread about 3.0 inches. 



