clinging specimens; at the same time, the removal of 

 rocks from the bottom dislodges the nonclingers which 

 are washed into the screen. In gravel or sand, the 

 upstream bottom is carefully stirred with hands or 

 garden fork, or the hands are used to "paddle" a 

 current of water across the bottom and into the screen. 



To minimize injury to the nymphs, frequent trips 

 should be made to the bank to remove them from the 

 screen. Nymphs are removed from the screen with 

 forceps or brush and placed in fresh water in a white 

 enameled pan about three-by-six inches in size and 

 two inches in depth. Ordinarily a low-power glass is 

 adequate for separating the different kinds of nymphs, 

 some of which usually go into 70 per cent alcohol 

 and others into rearing cages. 



In ponds and other quiet waters many specimens 

 can be taken by simply holding the hand screen close 

 to the bottom and "walking" it through the water. In 

 most instances it is necessary to rest the screen on 

 the bottom and across the knees, then paddle currents 

 of water across the bottom and through the screen, 

 the bottom-dwelling nymphs coming to the screen 

 with the current. If weeds are present, they are broken 

 and paddled into the screen and taken to the bank for 

 inspection. 



Where weeds are dense, or in collecting fossorial 

 nymphs that lie an inch or two below the mud or silt 

 surface of quiet or slow-moving water, the Ward's 

 Scraper Net is a great convenience. With scraper net, 

 shovel, or bucket, a scoop of mud, silt, or weed is 

 taken from the bottom and placed in a sixteen-by- 

 twenty-inch white enameled pan of six- or eight-inch 

 depth that is half filled with water. Gentle stirring 

 and further addition of water to the debris in the pan 

 soon brings to light any nymphs that may have been 

 captured. 



With some dampening of the collector, the hand 

 screen may be well employed in waters up to perhaps 

 . four feet in depth, but the Ekman Dredge should be 

 used for deeper waters. Bottom samples brought up 

 by the Ekman are handled in the large white enameled 

 pan. 



The single disadvantage found in using the all- 

 purpose hand screen is that a relatively coarse six- 

 teen-mesh wire cloth is necessarily used and very 

 small specimens may pass through the screen. Finer 

 mesh screens soon clog so that water currents wash 

 around the screen rather than through it. At each 

 collecting location, a few screenings should be made 

 in likely places with a two-foot square hand screen 

 made of twenty-four-mesh screen, this being brushed 

 clean after each immersion. 



Great variation in ecological conditions is ordi- 

 narily present even in a very short stretch of water. 

 Many mayfly nymphs are highly selective in their 

 habitat, and each possibility should be investigated 

 by the collector: fast and slow riffles both deep and 

 shoal; rock surfaces together with areas behind, in 

 front of, and between them; quiet water; trash beds 

 and leafy deposits — all should be carefully worked, 

 with particular attention given to shoals right at the- 

 edge of the stream. In working new waters, the col- 

 lector of mayfly nymphs should work the whole bottom, 

 always ready to expect the unexpected. 



81 



Day: Ephemeroptero 



If nymphs are to be added to the collection 

 such, they should be taken from the collecting screen 

 and placed immediately in four-dram vials of 70 per 

 cent alcohol, this fluid beLng drained and replaced 

 after a few days. 



Winged stages. — It is frequently possible to capture 

 mayflies in their first winged stajje as thej rise from 

 the surface of the water or as the) rest on stones 

 for a moment after omergenco. Those subimagoes, 

 together with those often found in shaded parte of 

 nearby shrubs and trees, can bo oasily reared to the 

 final adult, or imago, form. 



Subimagoes must be handled with oxtromo care as 

 the slightest injury will prevent transformation into 

 the desired imago. Tho ordinary aerial insect net, 

 wielded slowly and gently, can be used to capture 

 one flying specimen at a time, the specimen being 

 shaken individually into the open mouth of a paper 

 bag. Subimagoes at rest should be "urged" into the 

 paper bag by the slightest touch on wings or tails. 



A standard eightrinch Kraft paper bag with a six- 

 inch branch of leaves at the bottom and the open end 

 folded over provides a good housing for a half-dozen 

 subimagoes. The subimagoes will transform into 

 imagoes in from twelve to forty-eight hours and should 

 then be permitted to rest for another six or eight 

 hours after transformation in order to develop full 

 coloration. Then they should be placed in four-dram 

 vials of 70 per cent alcohol. 



Mayfly imagoes are most easily collected by means 

 of the insect net when engaged in their nuptial flight. 

 Different species swarm at different hours and may 

 be found over the water, near it, or more than a mile 

 from it. Most mayflies are poor fliers and usually 

 swarm in areas protected from the wind; some prefer 

 to swarm in bright sunlight whereas others are always 

 found in shade. If females are found depositing eggs 

 on the water, the direction of their approach may be 

 noted and followed to the swarm; collecting activities 

 of birds sometimes indicate the presence of swarming 

 mayflies. Flights are most easily detected when 

 looking directly toward the sun. 



Collected imagoes are taken from the aerial net 

 and placed directly into, four-dram vials of 70 per 

 cent alcohol, save for a few that go into the ethyl 

 acetate killing jar for color determinations. 



Rearing. — From the taxonomic standpoint, the rear- 

 ing of nymphs through the adult winged stages, with 

 consequent positive association of the life forms, must 

 be considered as a superior procedure in collecting. 



Field rearing is accomplished by placing a dozen 

 perfect and mature nymphs of a single species in a 

 sixteen-mesh copper wire screen cylinder about six 

 inches in diameter and eighteen inches long, one end 

 of which is permanently closed with copper screen. 

 With a stone in the bottom, or closed end, the cylinder 

 is placed upright in the stream in eight or nine inches 

 depth of water. A square of cheesecloth is fastened 

 over the open end with a rubber band, and a few leafy 

 branches are laid over the cage to give light shade. 

 In rain areas, a thin wooden cover is placed loosely 

 over the cheesecloth. 



The nymphs emerge and climb to the top of the 

 cage where they transform from subimago to imago. 



2-IOfl>L 



