Article IV. — The Zygoptcra, or Damsel-flies, of Illinois* By 

 Philip Garman, Ph.D. 



Introduction 



The order Odonata includes all insects known as dragon-flies in 

 the broad sense of the term. The adults are characterized by the 

 possession of fotir membranous, net-veined wings which are of nearly 

 equal size. The mouth-parts are fitted for biting and the metamor- 

 phosis is incomplete. The males are distinguished by accessory gen- 

 italia on the second and third abdominal sterna. The nymphs are 

 aquatic, and are recognizable and separable from other aquatic forms 

 by the large hinge-like labium which folds beneath the head. The 

 order is subdivided into two suborders, the Anisoptera and the 

 Zygoptera. The adults of the Anisoptera have large, broad wings, 

 but little contracted at the base and with numerous cross-veins. The 

 wings of the Zygoptera are usually narrowed at the base and possess 

 fewer cross-veins. The Anisoptera usually rest with wings spread 

 horizontally ; the Zygoptera usually with wings held vertically. The 

 nymphs of the suborders are easily separated by means of the respira- 

 tory apparatus, the Zygoptera having three tracheal gills at the caudal 

 end of the abdomen,, and the Anisoptera having no caudal tracheal 

 gills, being provided with rectal gills instead. 



The Odonata form one of the strangest orders of insects with which 

 an entomologist has to deal. Their bizarre form, striking colors, and 

 peculiar habits make them an object of much curiosity on tlie part of 

 the layman as well as the object of many studies on the part of the 

 scientist. The prevalence of the popular terms, snake-feeders, snake- 

 doctors, and similar names, shows that there are many superstitions 

 concerning the group. 



As is well known, the Odonata are predaceoiis, in all stages, upon 

 other insects, particularly upon those insects annoying to man, the 

 flies and mosquitoes, and in this role thev must be classed as beneficial. 

 Their harmful activities are few, but they sometimes destroy young 

 fish, they occasionally injure plants by the insertion of eggs, and, 



•Contributions from the Entomological Laboratories of the University of Illinois 

 No. 53. 



