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THE BioLtocy or EPpHypDRA SUBOPACA LOEW 583 
rocks, logs, or floating leaves near the surface for a considerable length 
of time, without attempting to make a change in place unless compelled. 
The locomotion may be classified into four modes. 
Crawling.— As the body is more or less cylindrical and smooth, and not 
equipped with specialized organs for swimming, the larva crawls most 
of the time at the bottom or on some object floating in water. Its pro- 
legs, although short, are equipped with well-developed claws for such a 
purpose. In the summer season, when it is cloudy, a number of larvae 
are often found crawling slowly on floating logs in the pools or on the soft 
mud bottom in the shallow, seldom disturbed water of the overflowed 
areas. The larva, in its way of progression, much resembles a cater- 
pillar, only that its prolonged caudal process is held upward like a cat’s 
tail, waving around, and sometimes even bending forward to touch upon 
the dorsum. Under bright sunshine, by the sudden brushing away of 
the floating scums, the larvae hiding in the shade beneath are put to 
“flight”’; however sluggish they seemed, they now begin to crawl faster, 
showing uneasiness under the suddenly changed conditions. This, of 
course, can only be attributed to the effect of light, which will be dis- 
cussed later. The larvae — most of them mature — have been found 
crawling on floating scums. In the laboratory aquarium the writer has 
seen a young larva crawl into an algal mass, become trapped with the 
filaments, and then struggle for freedom; being tangled with algae on 
the claws of its proleg, the larva was deprived of liberty, yet, because 
there was abundant food material in such a mass, it probably did not 
die, but attained maturity. 
Swimming by means of wriggling.— Wriggling is another mode of loco- 
motion generally employed by the larva. The body of the larva is not 
slender, consequently its wriggling is not so rapid and vigorous as that 
in some other aquatic dipterous larvae. But this larva, nevertheless, 
bends and twists itself freely in all directions. Its caudal process, natu- 
rally, is the most flexible part, whipping and lashing around to help in 
locomotion. It wriggles sometimes near the surface, sometimes near the 
bottom, or sometimes between the surface and the bottom, in no definite 
direction; but more frequently it ascends and descends in the water. 
After a shower or in the late afternoon of a clear day, a number of the 
larvae may be seen wriggling very slowly, each with one side of the body 
upward about an inch below the surface in open water. In wriggling, 
as well as in crawling, two or more larvae sometimes hold together by 
