4^2 Roosevelt Ji'ild Life- Bulletin - 



winged stage, live only to reproduce and die, or to fall a prey to 

 birds, mice and other animals. In -the streams of the Middle West 

 they are important as scavengers. They generally emerge in enor- 

 mous numbers, but for one day only, and then they are gone. In some 

 streams in Europe it has been noted that certain species emerge on 

 definite dates ; in fact, within stated hours on a given day, year after 

 year. Much speculation, but little evidence, exists as to the factors 

 which control this remarkable synchronism. 



In their aquatic stage the may-flies are of varied form, some of 

 them very flat and found under rocks (fig. 123), some swimming 

 about with quick, minnow-like darts, and some with elaborate gills by 

 means of which they propel themselves. All have gills for breathing 

 air from the water, some of the gills being thread-like, others flat, 

 and still others attached to slender stalks like leaves to a branch. 

 Some have elaborate processes on their heads for burrowing. These, 

 however, are found primarily in muddy streams, and in lakes and 

 ponds. In the mountain streams none of the burrowers occur. 



After transformation, the adults have two pairs of wings, the fore 

 wings large and triangular, the hind wings very small and inconspicu- 

 ous, indeed, sometimes entirel}- absent. Also, they generally have 

 from two to three fine tail filaments. 



In the mountain streams, their transformation is spread over a 

 considerable period, so that they are but little noticed. In the more 

 temperate and quiet streams they transform in one mass and fill the 

 air for a brief period for one or two days, and then disappear. 



Caddis-flics. — The third group, the caddis-flies, derive their name 

 from the fact that nearly all of them, in their aquatic stage, build 

 cases from bits of stone, wood, or fibres, or weave a net which they 

 attach to stones. These cases are infinitely varied in form, and 

 from the standpoint of craftsmanship are intensely interesting. In 

 the mountains one finds three types especially abundant. The first is 

 that of the "barnacle" caddis-worms {Rhyacophila sp. ), which build 

 their cases in large clusters from tiny stones (see fig. 127). The 

 second is that of the "picket" caddis-worms (Limncphilus sp.), 

 which build scjuare cases of neatly paralleled series of plant fibers. 

 Since the cases are fastened to the support by their bases and stand 

 out at right angles, the name "picket" is quite appropriate (figs. 126, 

 127). The third type is made up of extremely minute particles of 

 sand and secretion gummed together to form a conical, gently-curved 

 cornucopia about half an inch in length. Just before transformation, 

 caddis-flies, like moths and butterflies, go through a resting period, 

 called the "pupal" period, in which the change from grub to winged 



