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DEFENSIVE SPRAY MECHANISM OF A SILPHID BEETLE 
(NECRODES SURINAMENSIS)* 
By Thomas Eisner and Jerrold Meinwald 
Section of Neurobiology and Behavior, 
and Department of Chemistry, 
Cornell University, Ithaca, NY 14853 
Introduction 
Although much has been learned about chemical defenses of bee- 
tles in recent years (Weatherston and Percy, 1978), few studies have 
been made of Silphidae, the family that includes the largest carrion 
beetles. As is known to anyone who has collected these insects, 
many silphids respond to disturbance by emitting a nauseatingly 
malodorous ooze from the anus. The fluid is said to be strongly 
alkaline in some species, and rich in ammonia (Schildknecht and 
Weis, 1962). In Silpha, a gland had been noted that opens into the 
rectum (Dufour, 1826; Leydig, 1859), but no chemical work had 
been done to determine whether specific defensive chemicals in the 
anal effluent might stem from the gland. 
Personal observation had told us that one silphid, the so-called 
red-lined carrion beetle, Necrodes surinamensis, might be unusual. 
First, the beetle seemed able to eject its anal fluid as a spray rather 
than an ooze, which no other silphid had been reported to do, and 
second, the fluid gave an acidic test on indicator paper and had a 
stench that was overlain by a distinct aromatic fragrance. 
We have now studied N. surinamensis in some detail. Chemical 
work, carried out in collaboration with others, led to the isolation of 
several fatty acids and terpenoid compounds, present in the spray 
and produced by a special rectal gland. An account of these chem- 
ical findings, which are summarized in Figure 1, will be published 
elsewhere. We here give details of the beetle’s defensive behavior, 
plus a brief description of the gland, and data on the beetle’s unac- 
ceptability to predators. 
♦Paper No. 72 of the series Defense Mechanism of Arthropods. Paper No. 71 is 
Eisner, T. and Nowicki, S., Science 219, 185 ( 1983 ). 
Manuscript received by the editor October 12, 1982. 
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