A Philippine Land Crab Trap

Abstract

Residents of Malabuyoc on the west coast of Cebu in the Philippines use a bamboo tube trap for capturing the edible land crab Cardisoma carnifex. Traps are inserted into the mouths of occupied burrows where crabs are caught alive and unharmed as they emerge for nocturnal foraging. The technique of tube-trapping might prove useful in the scientific study of Car- disoma and other burrowing crabs and in selective harvesting of animals for consumption. DESCRIPTION AND USE OF THE TRAP The trap, which weighs 500 g, is assembled from five pieces of bamboo and a meter length of monofilament line (Fig. 1). Its design effectively exploits many of bamboo's useful properties-its shape, strength, flexibility, and lightness. The following description can best be understood by reference to Fig. 1. The body of the trap consists of a cylindrical section of bamboo stem with a length of 36.5 cm and inner diameter of 7.6 cm. The thickness of the wall is 0.7- 0.8 cm. A transverse nodal wall closes off the tube 8 cm from its posterior end. Four modifications have been made in the tube for the attachment or insertion of other components of the trap. The sliding door is held and guided in a rect- angular opening 1.7 cm wide and 2 cm deep that is sawed from the upper surface some 7 cm from the anterior end of the tube. The outer 0.3 cm of the bamboo wall behind the slot is split in a strip 2.5 cm wide for a distance of 8 cm. The split holds the crossbow in place at a right angle to the tube. The uppermost layer of the split is stripped away to form a flat surface where the slender spindle can be held securely while being inserted into notches on the back of the sliding door and trigger. Finally, an ovoid hole 2.3 cm wide is cut in the upper surface 23.5 cm back from the front of the trap. The trigger is inserted into the tube through this opening and hooked onto its anterior edge. The sliding door is a longitudinal, slightly concave section of stem 16.1 cm long and 4.9 cm wide. The lower and lateral margins are beveled for a close fit against the edge of the slot and the rounded floor of the trap. The door is notched both on its upper margin to receive the monofilament bowstring and on its concave face 12.5 cm below the upper margin for insertion of the spindle. When one end of the spindle is inserted into this notch and the other is held by the trigger, the sliding door is prevented from being snapped shut by the bow. The crossbow is a strip of bamboo stem 32.5 cm long, 1.6 cm wide, and 0.3 cm