DEFENSE MECHANISMS OF ARTHROPODS. 
II. THE CHEMICAL AND MECHANICAL WEAPONS 
OF AN EARWIG. 1 
By T. Eisner 
Department of Entomology, Cornell University, 
Ithaca, N. Y. 
The European earwig, Forficula ciuricularici Linn., possesses two 
pairs of small sac-like glands (Vosseler, 1890) situated dorsally in 
the abdomen, and opening on the posterior margins of the third and 
fourth abdominal tergites (text fig. 1). The principal active com- 
ponents of their secretion have recently been identified as 2-methyl, 
and 2-ethyl-/)-benzoquinone ( Schildknecht and Weis, i960). 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 of certain 
other insects are, in fact, extraordinarily effective repellents (Eisner 
!958a, 1958b). 
In addition to the glands, Forficula possesses the typical dermapteran 
pincers, and these too have been claimed to play a defensive role (in 
addition to other roles, including prey capture), although the evi- 
dence is here again circumstantial at best (Burr, 1910; Gadeau de 
Kerville, 1905; Rau, 1933). 
The purpose of this note is to present the results of some experi- 
ments designed to test whether the glands and pincers are really the 
effective defensive devices they were presumed to be.' J 
The Pincers 
In order to facilitate close-range observation of the earwigs, they 
were attached to rods (by a technique used previously and already 
described in detail: Eisner 1958a, 1958b; Eisner et ah, 1959), and 
adjusted to a normal stance on the substrate as shown in Plate 7, 
figure 1. In this way they were prevented from scurrying about, while 
at the same time retaining full mobility of head, abdomen, and legs. 
By subjecting such animals to mild traumatic stimuli, applied locally 
to the body or to individual appendages by pinching with fine forceps 
or touching with a warm needle, it was possible to witness very clear- 
ly the way in which the pincers are put to a defensive use. 
This study was supported by Grant E-2908 of the U. S. Public Health 
Service. 
2 Forficula auricularia is established in the U. S. A. The specimens used 
were taken in Lexington, Mass. 
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