148 POND COMMUNITIES 



caddis-worms (Phryganeidae: Neuronia) (Fig. 99), which are also abun- 

 dant in the later stages of dense vegetation. This worm's case is some- 

 what similar in form to that of Leptoceridae, being a circular tube, but it 

 is made of pieces of grass blades or other pieces of plant fragments instead 

 of sand grains. The pieces are fastened together with silk. The worm is 

 found creeping among the vegetation, drawing its case after it. Amnicola 

 (Fig. 100), the river-dwelling snail, is common, especially on twigs and 

 logs. In the mature stage represented by Pond 14 (Fig. 10 1) the com- 

 mon newt (Fig. 102) probably reaches its maximum abundance. The 

 snails which are at best advantage in these ponds are the lung breathers. 

 They can here come to the surface for air, and food is abundant, as the 

 surfaces of the plants are covered with algae and these form the food of 

 the snails. Those snails which come to the surface for air are common. 

 Planorbis campanulatus (Fig. 103) is characteristic of the mature stage 

 and Lymnaea refiexa (Fig. 104) in the older stages. The individuals in 

 this case are larger than those of the temporary marshes (cf. Figs. 104 

 and 125, pp. 149, 175). Planorbis parvus (Fig. 105) is commonest in the 

 earliest phases and Planorbis hirsutus (Fig. 106) in the later. Diving 

 beetles (Fig. 107), which are common throughout, are most numerous 

 in the denser vegetation. The soldier-fly larvae (Fig. 108) are often 

 common in the dense filamentous algae of the mature phases of the asso- 

 ciation; here the number of all dipterous larvae is greater than at any 

 other point. Midge larvae occur in great numbers, having their cases 

 among the algae. Horseflies (Fig. 92), also T any pus, Ceratopogon, and 

 some mosquitoes are present. Specific identification, however, is not 

 possible, and whether or not the species differ in modes of life or reactions 

 from those inhabiting the earlier stages in the pond series has not been 

 determined. 



Adult aquatic insects have increased with the increase in vegetation, 

 in a remarkable fashion. The prominent forms are the larger bugs, such 

 as the electric-light bugs (Zaitha fluminea and Belostoma americana 

 Leidy, with Benacus griseus Say). The water-boatmen are also common. 

 The species of these are not well known, and we cannot say whether or 

 not they are the same in the older and younger ponds. Back-swimmers 

 are also abundant {Notonecta variabilis and undulata, Buenoa platycnemis, 

 and the small form, Plea striola, occur here). They are few in number 

 or absent from the younger ponds. 



Some animals particularly abundant in the older stage are the 

 common leech {Placobdella parasitica) (Fig. 109), the larvae of a netted- 

 winged insect (Chauliodes rastricornis) (Figs, no, in), the large flat 



