Defense Mechanisms of Arthropods. II. The Chemical and Mechanical Weapons of an Earwig

The European earwig, Forficula auricularia Linn., possesses two pairs of small sac-like glands (Vosseler, 1890) situated dorsally in the abdomen, and opening o.n the posterior margins of the third and fourth abdominal tergites (text fig. ). The principal active com- ponents of their secretion have recently been identified as 2-methyl, and 2-ethyl-p-benzoquinone (Schildknecht and Weis, 96o). The glands have always been suspected to serve in defense against pre- dators, and this suggestion, although advanced originally in lack of evidence, appears recently to have received at least indirect support, since it is now known that the quinone-containing secretion ot certain other insects are, in fact, extraordinarily effective repellents (Eisner 958a, 1958b).