アリジゴクの食餌における道具使用行動について

The tool-using behavior in the ant-lions (the larvae of the Myrmeleon formicarius) was observed in detail and experimented analytically. This behavior is the throwing-up of sand by the ant-lions to capture the preys, namely, Formica japonica, Aphenogaster famelica and Lasius niger, if they try to escape out of the pits. In each experiment a new individual of these three species of ants was used. Several results obtained were reported in the present paper.<BR>1) Six patterns, i. e., BC, BC, BCTC, BCTC, TC and TC were discriminated in the feeding behavior. Excepting two patterns, BC and BC, each one of them includes the sand-throwing-up or tool-using behavior.<BR>2) The tool-using behavior is resulted in the ant-lions as a kind of direct or indirect chain responses following the completion of nest building. The sign stimulus in this tool-using behavior is a kind of mechanical stimuli, that is, the extremely faint pressure given by the ant to the side wall of the pit. The tool-using behavior is determined by three factors : 1) the preceding of the biting behavior, 2) the bodily condition (the elongation of sand-throwing-up distance as a result of bodily growth) and 3) the position of the prey (within or beyond the capturing area).<BR>3) When the value of a ratio of the diameter of the pit to twice the length of the the generating line, D/2L cos α (the angle between D and L), is 0.654 in pattern B of the ant-lions and 0.697 in pattern C, their tool-using to prey the ants is most effective.<BR>4) The rate of capturing the prey by the ant-lion increases with age. It is apparently found that the increase of this rate depends upon both the enlargement of the capturing area with the increase of size of the pit and the lengthening of the sand-throwing-up distance as the result of growth of the bodily mechanism.<BR>5) The sand-throwing-up has the survival value next to the biting behavior in capturing preys.<BR>6) This sand-throwing-up is a kind of instinctive tool-using behavior. But the older the ant-lion grows, the more effective the tool-using behavior becomes, because the animal has many chances of sand-throwing-up with age. In other words, the sand-throwing-up is seemed to include a kind of learned behavior. As some valid evidences we can point out increase of the rate of capturing preys caused by both a few sand-throwing-up and a small number of hits at the preys with age.