Capture of Bombardier Beetles by Ant Lion Larvae

Ant lions (larvae of Myrmeleontidae) are well-known for their unique method of prey capture (Wheeler, 1930). They construct a conical pit in the sand and lie buried at the bottom with only their sickle-shaped mandibles, or head and mandibles, exposed. When a n ambulatory arthropod falls into the pit it is seized and pierced by the mandibles and sucked dry. Bombardier beetles, like other Carabidae, are ground foragers and thus may be expected to fall into ant lion pits. However, due to their singularly effective chemical defense, some question remained whether they might be vulnerable to capture by ant lions. Bombardier beetles respond to attack by ejecting an aimed spray of hot (lOO°C repellent quinones from the tip of the abdomen (Eisner, 1958; Aneshansley et a/., 1969). The spray is an effective deterrent to a number of insectivores (Eisner, 1958; Eisner and Dean, 1976). Several authors (Turner, 19 15; Wheeler, 1930; Lucas and Brockmann, 1981) have observed that ant lions may pull their prey under the sand after grasping it. Lucas and Brockman (1981) suggest that this behavior may protect ant lions from aggressive prey. We here report that ant lions can capture bombardier beetles providing the ant lions have pulled their head beneath the sand by the time the beetles eject their spray. Our observations were made at the Archbold Biological Station, Lake Placid, Highlands County, Florida, where the ant lions (Myrmeleon crudelis larvae) and bombardier beetles (Brachinus spp.) were taken. Fifteen ant lions were placed in each of three metal boxes (30 X 44 X 18 cm high) filled with sand to a depth of 8 cm. After the ant lions had constructed pits, bombardier beetles were released individually into the boxes and observed until they slid o r walked into a pit and were seized by an ant lion. Two things were noted each time a beetle "fired" after being grasped: (1) whether the