AQUATIC INSECTS OF FRESHWATER 
the end of the abdomen out of the water, jerking it under and quickly 
crossing the hind legs over it, then descending to the nest and by opening 
the legs the air bubble escapes into the nest. The hairs on the body keep 
the surface from becoming wet, and in the nest the spider is as dry as on 
land. ‘The 40 to 100 cocoons, containing the round saffron-colored eggs, 
are laid in the nest during June, and in July the young are large enough 
to spin a nest of their own. Another family of the eight-eyed group, the 
Lycosidz, have semi-aquatic genera which almost exclusively live on the 
banks of ponds and streams and prey upon aquatic insects, chasing them 
on the surface of the water. Some species grow-to nearly one inch in 
length. Other smaller species are of similar habit. These often dive below 
the surface when pursued by enemies from above the water or when in 
pursuit of their prey. 
Acarina. This family consists of the lowest order of the Arachnide, 
which live in the earth and in both fresh and salt water. They comprise 
the Mites and Ticks which differ from other Arachnids in their oval or 
rounded forms, which are not articulated. The mouth parts are developed 
for biting and sucking and they breathe by tracheal gills. Of this family 
the Water-mites are known as Hydrachnide, which have soft, oval un- 
segmented bodies, and limbs adapted for swimming, terminating with 
adhesive vesicles. They are parasitic on fishes and mussels, while some 
of the smaller species live on the Hemiptera, Coleoptera and other insects. 
The most generally distributed genera are Hydrachna, Atex, Limno- 
chares and the marine Pontarachna. Atex hasan oval solid body of bright 
red color with curved, clawlike mandables, acute, pointed maxillaries, and 
short, weak legs. ‘The species inhabit some of the mussels, 4. ypsilophorus 
in Anadonta and 4. humorosa in Unios. ‘The eggs are laid in the spring 
on the stems of water plants and when hatched seek hosts in which to pass 
their subsequent existence. A bright red species, Bdella maritima, occurs 
under stones between tidemarks. Three species of Trombidium are re- 
presented in the United States, all of red color. 
HypracHNna or WaArTeER-MITES, are common in ponds. They are 
tenacious of life and steadily move about by the rapid movements of 
their fringed legs. The larve have six and the adult 
eight legs, which increase in length, with the posterior 
pair the longest. The body is slightly convex, the 
mandables needle-shaped, the third joint of the max- 
illa the longest, and all the species have two distinct 
eyes. They are parasitic on both fishes and mussels, 

FIG. 234. Water-mite, 
Hydrachna geographica. ' . 
Enlarged. and are frequent external freshwater parasites, easily 
detected by their size. The largest and most widely distributed form is 
H. geographica, Fig. 234, while H. globosa and H. triangularis are also 
frequently occurring species. 
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