6 FARMERS” BULLETIN 734. 
of the cone is formed by cutting off the apex, as previously described, 
it is ready for insertion in the trap. 
In order to figure the distance around the base of a cone of any 
given diameter, multiply the diameter by 3.1416 or 3}. 
The height of the legs of the trap, the height of the cone, and the 
size of the aperture in the top of the cone, each are of importance 
in securing the greatest efficiency. 
OTHER FORMS OF CONICAL TRAPS. 
Conical traps with steel frames are satisfactory, but they are less 
easily resereened and it is more difficult to keep the lids closely fitted. 
These, of course, can 
be constructed only 
by shops with con- 
siderable equipment. 
Traps _ constructed 
with a wooden disk 
about the base of the 
cone, and a similar 
disk around the top 
to serve as a frame, 
or those with a square 
wooden frame at the 
bottom and top with 
strips up the corners 
are fairly  satisfac- 
tory. It should be 
borne in mind that 
the factor which de- 
termines the number 
of flies caught is the 
ic. 4.—Tent flytrap. When the trap is set up the screen 
box, A, fits on the base, B, and two pans of bait are 
placed beneath the tent. ©, Hole in screen at apex of diameter of the base 
tent. (Original.) . 
ic vena of the cone, if other 
things are equal. Therefore the space taken up by the wooden 
framework is largely wasted, and if it is too wide it will have a 
deterrent effect on the flies which come toward the bait. For this 
reason it is advisable that the wood around the base of the cone 
should be as narrow as consistent with strength—usually about 3 
inches. 
lnder no condition should the sides or top of the trap be of solid 
material, as the elimination of hght from the top or sides has been 
found to decrease the catch from 50 to 75 per cent. 
TENT TRAPS. 
The tent form of trap has been widely advocated in this country, 
but recent experiments indicate that it is much less efficient than the 
