The Size of the Trap.The conical hoop trap consists essentially of a screen cylinder with a frame made of barrel hoops, in the bottom of which is inserted a screen cone. The height of the cylinder is 24 inches, the diameter 18 inches, and the cone is 22 inches high and 18 inches diameter at the base.
Materials. Material necessary for this trap consists of Four new or secondhand wooden barrel hoops.
One barrel head.
10 feet of strips 1 to 1 1/2 inches wide by 1/2 inch thick (portions of old boxes will suffice).
61 linear inches of 12 or 14 mesh galvanized screening 24 inches wide for the sides of the trap, and 41 inches of screening 26 inches wide for the cone and the door. An ounce of carpet tacks.
Two turn-buttons, which may be made of wood.
The total cost of the material for this trap, if all is bought new at retail prices, is about 65 cents. In practically all cases, however, the barrel hoops, barrel head, lath, and strips can be obtained without expense. This would reduce the cost to that of the wire and tacks, which would be 45 cents. If a larger number of traps are constructed at one time, the cost is considerably reduced.
Construction of the Trap.One of these traps is illustrated in Fig. 143. In constructing the trap, two of the hoops are bent in a circle (18 inches in diameter on the inside), and nailed together, the ends being trimmed to give a close fit. These form the bottom of the frame, and the other two, prepared in a similar way, form the top.
The top of the trap (Fig. 144) is made of an ordinary barrel head with the bevel edge sawed off sufficiently to cause the head to fit closely in the hoops and allow secure nailing. A square, 10 inches on the side, is cut out of the center of the top to form a door. The portions of the top (barrel head). are held together by inch strips (D) placed around the opening 1/2 inch from the edge to form a jamb for the door. The door consists of a narrow frame (E) covered with screen (F), well fitted to the trap and held in place (not hinged) by buttons (G).
The top is then nailed in the upper hoops, and the sides are formed by tacking screen wire closely on the outside of the hoops. Four laths (or light strips) are nailed to the hoops on the outside of the trap to act as supports between the hoops,- and the ends are allowed to project 1 inch at the bottom to form legs.
The cone is cut from the screen, and either sewed with fine wire or soldered where the edges meet. The apex of the cone is cut off to give an aperture 1 inch in diameter. The cone is then inserted in the trap and closely tacked to the hoop around the base.
Construction of the Cone.The construction of a cone of given height or diameter is quite simple if the following method is followed. It is best to cut a pattern from a large piece of heavy paper, cardboard, or tin. Fig. 145 illustrates the method of laying out a cone of the proper dimensions for the above trap.
An ordinary square is placed on the material from which the pattern is to be cut. A distance (22 inches) equal to the height of the cone is laid off on one leg of the square at A, and a distance (9 inches) equal to one half of the diameter of the base of the cone is laid off on the other leg at B. A line is then drawn between the points A and B.
With the distance between these points as a radius and with the point A as a center, the portion of a circle C D is drawn. With a pair of dividers, the legs of which are set 1 inch apart, or with the square, lay off as many inches on the arc C D, starting at C, as there are inches around the case of the cone-in this case about 56 1/2 inches, reaching nearly to the point E. Then add 1/2 inch for the lapping of the edges of the cone, and 1/2 inch which is taken up when the cone is tacked in, thus making a total distance from C to E of 57 1/2 inches. Draw a line from A to C and another from A to E, and cut out the pattern on these lines and on the arc from C to E, as shown in Fig. 145. The edges A C and A E are then brought together, lapped 1/2 inch, and sewed with wire or soldered.
After the aperture 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 1/7.
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.
The Bait for the Trap.The trap may be baited with milk or a mixture of water and molasses that has been allowed to ferment. Crushed overripe fruit is also effective, especially if combined with milk. The water and molasses mixture should not be used if there are honey bees near by, since it attracts them in great numbers.
The bait should be placed in a shallow pan about four inches smaller in diameter than the bottom of the trap. The pan is set upon the ground under the cone; the flies rising from the bait pass through the hole at the top of the cone and into the trap.