AQUATIC INSECTS 917 



KEY TO THE ORDERS OF AQUATIC INSECT LARVAE 



1 (8) Larvae with wings developing externally (called nymphs in this chapter) 



and no quiescent pupal stage 2 



2 (7) With biting mouth parts 3 



3 (6) With long, filamentous caudal setae; labium not longer than the head, 



and not folded on itself like a hinge 4 



4 (s) Gills mainly under the thorax; tarsal claws two; caudal setae two 



(Stoneflies; see page 883) . . Plecoptera 



5 (4) Gills mainly on the sides of the abdomen; tarsal claws single; caudal 



setae generally three. (Mayflies ; see page 921).. Ephemerida. 



6 (3) Caudal setae represented by three broad, leaf-hke 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 fore legs. 

 (Dragonflies and damselflies; see page 923) . . Odonata. 



7 (2 Mouth parts combined into a jointed beak, which is directed beneath 



the head backward between the fore legs. 



(Bugs; see page 933) . . . Hemiptera. 



8 (i) Larvae proper, with wings developing internally, and invisible till the 



assumption of a quiescent pupal stage 9 



9 (18) With jointed thoracic legs 10 



10 (11) With slender, decurved, piercing mouth parts, half as long as the 



body; small larvae, living on fresh-water sponges. 

 Family Hemerobiidae (see page 934) of . . Neuroptera. 



11 10) With biting mouth parts 12 



12 (15) With a pair of prolegs on the last segment only (except in SiaUs, 



Fig. 1367, 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. . . 13 



13 (14) Abdominal segments each with a pair of long, lateral filaments. 



Family Sialidtoae (see page 935) of . . Neuroptera. 



14 (13) Abdominal segments without long, muscular, lateral filaments, often 



with minute giU filaments cyhndric larvae, generally living 

 in portable cases. (Caddisflies; seepage 936). . Trichoptera 



15 (12) 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 want- 

 ing 16 



16 (17) With five pairs of prolegs, and with no spiracles at the apex of the 



abdomen. . . (Moths; see page 903) . . Lepidopteia. 



17 (16) Generally without prolegs; never with five pairs of them; usually 



with terminal spiracles; long, lateral filaments often present 



on the abdominal segments. 



(Beetles, adults; seep. 937; larvae; seep. 943) . Coleoptera 



18 (9) Without jointed thoracic legs; with abdominal prolegs, or entirely 



legless (FHes, etc.; see page 943) . . Diptera, 



