BEHAVIORAL ADAPTATIONS OF AN AFRICAN PONERINE ANT IN THE CAPTURE OF MILLIPEDES

Abstract

Abstract Workers of the ponerine ant Plectroctena minor are equipped with hypertrophied mandibles that can seize tubular millipedes, their essential prey, of up to 4 mm in diameter. We studied their predatory behavior in four situations where they captured spirostreptid millipedes. (1) P. minor workers generally seized millipedes of less than 4 mm in diameter dorsally and by their anterior part. During seizure the mandibles slipped on the exoskeletal coils of the millipede body and were caught between two segments that were slightly separated by the strong pressure. This facilitated stinging that mostly occurred ventrally in the soft intersegmentary space of the seized zone. (2) When a millipede was more than 4 mm in diameter, the workers seized it by an appendage before stinging or by wrapping themselves around the prey, then recruited nestmates in order to retrieve it. (3) The workers probably perceived kairomones from millipedes rolled into sloughing lodges as they opened the lodges and singly captured individuals less than 4 mm in diameter. Larger individuals (more than 4 mm in diameter) were captured after the workers recruited nestmates that generally cut up these prey on the spot. (4) When encountered in a test-tube simulating galleries, 95 to 105 mmlong millipedes (around 8 mm in diameter) were always captured. When the millipede's head was near the test-tube opening, the workers gripped the antennae or mandibles and stung the extreme anterior part of the millipede body, triggering rapid paralysis. In this case, they were even able to singly master then to retrieve these millipedes 94 to 117 times their weight, which represents the highest ratio for a solitary hunting strategy in ants. When the hind part of the millipede was near the test-tube opening, seizure was difficult and nestmates were recruited in most cases. We concluded that the behavioral flexibility of P.minor, which mainly occurred during the solitary phase of prey mastering, permitted the capture of millipedes of a wide range of sizes.