Discharge by a Female Ground Beetle, Pterostichus lucublandus (Coleoptera: Carabidae), Used as a Defense against Males1

Abstract

Many species of insects are known to discharge fluids from the end of the abdomen to repel predators such as snakes, birds, rodents, or even other insects. When such a defensive substance is expelled as a gas or liquid onto a pursuing enemy, it usually distracts or incapacitates the attacker long enough for the intended victim to escape, (iround beetles of the genus Brachinus, commonly called bombardier beetles, are most noted for this tactic (Eisner 1958), but many carabid species in other genera are also capable of expelling a deterrent substance (Eisner 1958, Ball 1960, Eisner et al. 1963, Schildknecht 1970). Schildknecht and his colleagues (Schildknecht 1970) examined the fluids from the pygidial glands of 20 species of carabids, including 5 species of the genus Pterostichus, and found 19 of them to be mostly methacrylic and tiglic acids, both of which they designated as cytotoxins which function in defensive mechanisms. However, the literature does not indicate that the predator suffers more than a temporary disabling, and most recover within a few minutes. Insects normally cease attacking and spend 15–30 sec vigorously trying to clean their antennae and mouth parts with their feet or by rubbing them on the ground (Eisner and Meinwald 1966). Some experience an immediate and brief period of seizures during which their legs are so convulsed that locomotion is impossible, which suggests that the spray acts as a transient poison (Eisner 1958).