HOW TO KNOW THE IMMATURE INSECTS 



NAIADS 



In mythology, a naiad was one of the nymphs believed to live in, 



and give life and perpetuation to lakes, rivers, springs and fountains. 



In entomology, the term naiad is applied to the nymph with aquatic 



habits. There are al- 

 together only three or- 

 ders of insects which 

 possess immature 

 stages that are termed 

 naiads. These are the 

 Plecoptera, Ephemerop- 

 tera and Odonata. The 

 naiads have some char- 

 acters in common. All 

 naiads are aquatic (ex- 

 cept a few exotic spe- 

 cies); they have closed 

 spiracles, breathe by 

 means of gills, and 

 have mouth parts of 

 the chewing type. Most 



of them are predacious, but the naiads of Ephemeroptera are believed 



to be herbaceous. 



Naiads are generally quite uniform in appearance. The legs are 

 long, the body is flattened and campodeiform and they are very ac- 

 tive in water. The naiads of Plecoptera and the Ephemeroptera have 

 conspicuous caudal filaments, varying from two to three 

 in number. In the damselflies (Zygoptera), the caudal 

 appendages are modified into leaf-like form and known 

 as tracheal gills. Tracheal gills are located on various 

 parts of the body. In Plecoptera, they are usually lo- 

 cated on the underside of the thorax, although some 

 species have gills on the head or on the abdomen. In 

 Ephemeroptera, the gills are located on the abdomen. 

 In the dragonflies, the rectum is modified to form a tra- 

 cheal gill chamber. In the damselflies, there are three 

 plate-like gills at the posterior end di the abdomen. 



Fig. 21. Rectal 



tracheae of 



dragonfly. 



Fig. 20. Naiads: damsel fly (Odonata); b, stonefly 

 (Plecoptera); c, Mayfly (Ephemeroptera). 



LARVAE 



The term larva is derived from the Latin word for mask, having 

 reference to the ancient belief that the adult form was masked or ob- 

 scured in the larva. In entomology, the larva applies to the immature 

 stage between the egg and the pupal stages of the insects with com- 

 plete metamorphosis. There are several characters in common. A lar- 

 va has no trace of wings and compound eyes are never present. The 



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