PART I 



AIDS TO RECOGNITION OF FRESH-WATER 



ORGANISMS 



KEY TO THE ORDERS OF AQUATIC INSECT LARVAE 



1 — Larvffi with wings developing externally (called nymphs in this book) and no quiescent 



pupal stage 2 



LarvcB proper, with wings developing internally, and invisible till the assumption of a 

 quiescent pupal stage : form more worm like 5 



2 — With biting mouth parts 3 



— Mouth parts combined into a jointed sucking beak, which is directed beneath the head 

 backward between the forelegs. (Bugs; see page 20) Hemiptera 



3 — With long, slender tails; labium not longer than the head, and not folded on itself like 



a hinge 4 



— Tails represented by three broad, leaf-like respiratory plates traversed by tracheae, 

 or by small spinous appendages; labium when extended much longer than the head; 

 at rest, folded like a hinge, extending between the bases of the forelegs. (Dragonflies 

 and damselflies; see page 14) Odonata 



4 — Gills mainly under the thorax; tarsal claws two; tails two. (Stone flies; see page 7) 



Plecoptera 



— Gills mainly on the sides of the abdomen; tarsal claws single; tails generally three. 

 (Mayflies; see page 8) Ephemerlda 



5 — With jointed thoracic legs 6 



— Without jointed thoracic legs; with abdominal prolegs, or entirely legless. (Flies^ etc.; 

 see page 28) Diptera 



6 — With slender, decurved, piercing mouth parts, half as long as the body; small larvas, 



living on fresh- water sponges. Family Hemerobiidae (see page 30) of. .Neuroptera 



— With biting mouth parts 7 



7 — ^With a pair of prolegs on the last segment only (except in Sialis, plate 13, which has 

 a single long median tail-like process at the end of the abdomen) these directed 



backward, and armed each with one or two strong hooks or claws 8 



— Prolegs, when present, on more than one abdominal segment; if present on the last 

 segment, then not armed with single or double claws (except in gyrinid beetle 

 larvae, which have paired lateral abdominal filaments), often entirely wanting. .9 



8 — Abdominal segments each with a pair of long, lateral filaments. Family Sialididae 



(see page 30) of Neuroptera 



— Abdominal segments without long, muscular, lateral filaments, often with minute gill 

 filaments; cylindric larvae, generally living in portable cases. (Caddisflies; see 

 page 24) Trichoptera 



9 — With five pairs of prolegs, and with no spiracles at the apex of the abdomen. (Moths; 



see plate 13) Lepldoptera 



— Generally without prolegs; never with five pairs of them; usually with terminal spir- 

 acles; long, lateral filaments sometimes present on the abdominal segments. (Bee- 

 tles; see page 26) Coleoptera 



5 



