364 
Psyche 
[Vol. 87 
Discussion 
The discovery of a chemical defense mechanism in an insect 
should come as no surprise, since such mechanisms are extra- 
ordinarily widespread among arthropods. Moreover, many insects, 
including a multiplicity of beetles, termites, ants, earwigs, cater- 
pillars, and phasmids, eject their defensive secretions in the form of 
accurately directed jets. Necrodes is anomalous in that it expels its 
aimed secretory discharges from the anus. Other beetles that spray, 
such as Carabidae, also discharge from the tip of the abdomen and 
may aim their ejections by movement of the abdominal tip (e.g. 
Eisner, 1958), but their glands are integumental and open beside the 
anus on the body wall itself. Necrodes is further unusual in that it 
has only one gland. Exocrine defensive glands in beetles commonly 
occur in pairs. 
It seems reasonable to presume that the gland of Necrodes arises 
developmental^ as an outpocketing of the rectum. Other rectal 
glands in Silphidae, such as that of Silpha, are doubtless homolo- 
gous to that of Necrodes. We feel this to be so despite some differ- 
ences in gland morphology [In Silpha americana the lateral tubule is 
reduced to a short elaborately subdivided diverticulum (Alsop, 
1970)]* and in gland chemistry ( Silpha americana, as we shall report 
elsewhere, produces steroids in its gland). While in the absence of 
histological work little can be said about the function of the two 
parts of the Necrodes gland, the strongly muscled condition of the 
sac suggests that it might serve as the reservoir from which secretion 
is expelled for the discharge. The tubule might be strictly secretory. 
It seems clear from the tests with ants and birds that Necrodes is 
relatively unacceptable to such predators. But to what extent this is 
attributable to the glandular components of the spray, or to enteric 
additives of the spray, or even to entirely different factors (carrion 
contamination of the beetle’s body?) remains to be seen. The secre- 
tion, no doubt, plays a defensive role, but the other factors may 
amplify the effect. It is interesting in this connection that another 
common inhabitant of carrion, the staphylinid beetle Creophilus 
*Dufour ( 1826) writing of Silpha littoralis, speaks of a rectal gland with a “vaisseau 
secreteur” almost as long as the body, suggesting that he was dealing with a gland 
similar to that of Necrodes. 
