i 



55 



Lottin: Introduction 



17 - 9 ' steel 

 fines — '/+ ' diam 

 End* are pointed 



Conical shaped net 



weiijh t 

 at tacfiea at end 

 of 4 - ?-'/2 ' Strand,, 

 of wire fastened 

 to eyelets. 



Vb " steel pi a tes 

 welded together. 



Intro, fig. 78. Drag-typo sampler showing structural details 

 (Usinger and Needham, 1956). 



Intro, fig. 79. Submerged trap, used to sample free-swimming 

 fauna in ponds (W. R. Kellen). 



are useful in sampling known areas of stream or lake 

 bottoms, particularly for Trichoptera, Ephemeroptera, 

 Plecoptera, Odonata, and Diptera. One type is the 

 tent trap (Needham, 1908; Sprules, 1947). This is 

 a cage that is set on the bottom in the shallow water 

 of a stream, for example, with a large part projecting 

 above the surface. Adult insects emerge and fly or 

 crawl up onto the screen, and are removed from time 

 to time through a door on the side. In streams, care 

 should be taken to keep the upstream side of the 

 cage clean of debris that might slow down the current 

 and thus alter the habitat. On lakes, floating tent 

 traps have been used by Adamstone and Harkness 

 (1923) and others (intro. fig. 81). 



Inverted cone emergence traps or "funnel traps" 

 have been used to sample insects as they emerge from 

 the bottom of ponds or lakes. These cones are sub- 

 merged to various depths (Brundin, 1949) and held 

 by anchors or wires where they catch the midges or 

 other organisms which emerge over a given area (intro. 

 fig. 80). The underwater cones catch pupae which may 

 go on to molt in the air trapped in the tube at the 

 small end of the cone. Emergence traps are partic- 

 ularly useful in studies of the turnover or the annual 

 crop of bottom organisms in contrast to the standing 

 crop measured by other samplers. A comparison of 

 such sampling techniques is given by Guyer and 

 Hutson (1955). 



The submerged "fly" trap (intro. fig. 79) is con- 

 structed along the lines of a standard fly (rap; that is, 

 it consists of a square screen cage with an inverted 



