Bioacoustics of Chiasognathus grantii

Remarks . Stephens (1831) described C. grantii based on a single holotype specimen. This specimen was found in the University of Cambridge Museum of Zoology, U.K. The holotype was likely part of the Stephens collection that was acquired by the Cambridge Philosophical Society. The entire insect collection of the Cambridge Philosophical Society was turned over to the University of Cambridge in 1865 as the foundation of a museum collection at the university. Unfortunately, none of the Stephens specimens were properly labeled so we had to match the attributes of this particular specimen to the original illustrations of Stephens (1831) to verify that it is the holotype . The male mandibles of this species can display great variation in their length, thickness, and curvature, and this specimen perfectly matches the specific curving and unusually large and thick mandibles of the original illustration. Specimens of such great size are relatively rare, and the general way the specimen is mounted also closely matches the original illustrations. The fact that this specimen was the only C . grantii specimen found in the University of Cambridge Museum of Zoology (the subsequent depository of Stephens’ collection) and that it matches the original description and illustrations gives us enough evidence to state that this specimen is the holotype . Stephens (1831) reported that a Chilean collected this specimen in January on Chiloé Island and gave it to Dr. Grant, who was the surgeon on board the H.M.S. Forte. The immense variation in size in this species has prompted the continued use of the name ‘ pygmaeus’ for the smaller males despite any evidence that would suggest distinct populations or genetic uniqueness. The idea remains tempting to amateur collectors, possibly because even these smaller males are of a similar size (and show the same amount of allometric development) as male majors of other species such as C. mniszechii . The development of male majors in C. grantii that are twice-again as large, and how this relates to the breeding behavior of the species, is something that deserves to be studied in more detail. Benesh (1960) , and thus Krajcik (2001) , listed C. pygmaeus under synonymy with C. latreillei despite the photograph in the original that clearly depicts a small C. grantii . Nevertheless, this demonstrates the existence of some confusion about the taxon and that the designation of a neotype is warranted. Natural History. Grant’s stag beetle, sometimes referred to as Darwin’s stag beetle, is the largest species in the genus and one that commands a great deal of attention. Other common names for the species include ciervo volante, llico-llico, and cantábria. The species was observed by Darwin in Chile ( Darwin 1871 ): “The male Chiasognathus grantii of South Chili – a splendid beetle … has enormously-developed mandibles; he is bold and pugnacious; when threatened on any side he faces round, opening his great jaws, and at the same time stridulating loudly; but the mandibles were not strong enough to pinch my finger so as to cause actual pain.” Darwin’s observations were expanded by Joseph (1928) and Hamilton (2000) with further discussion on the behavior of C . grantii males. To this we add our own observations made while collecting in Chile . Males of C . grantii are energetic and will attempt to pinch with their elongate mandibles when handled. As noted by Arrow (1951) , the bite of a female would be much more painful, although the sharp mandibular apex of males can draw blood (ABTS, personal observation). Males will raise up on their middle and hind legs when threatened or when approached by another male (Fig. 1). When another male is introduced, the two individuals will move together and adopt this aggressive posture and will then battle each other. Each will attempt to grip with their mandibles around the lateral teeth of the pronotum of their opponent. Once a strong grip is established there is an attempt to lift the opponent and drop it to the ground. When a female is introduced, the successful combatant will adopt an apparent mate-guarding stance with his mandibles and legs arched over the female (Fig. 2) and will battle any other males that approach. Hamilton (2000) reported that male combat occurs either in trees, where the females feed on sap, or among the flowers of the native canelilla, a climbing hydrangea ( Hydrangea serratifolia (H. et A.) F. Phil ( Hydrangeaceae )). Adults have been reported to feed on the sap of Nothofagus betuloides (Mirbel) Oersted , N. nitida (Phil.) Krassen , N. obliqua (Mirbel) Oersted (Fagaceae) , and Weinmannia trichosperma Cav. (Cunoniaceae) ( Joseph 1928 ; Vergara and Jerez 2009 ). As with other chiasognathines, larvae live in the soil ( Joseph 1928 ). Adults may be seen flying just before dark and are attracted to light. Arrow (1904) discussed the stridulatory mechanism present in adults of both sexes of C. grantii , and that it is composed of a ridged elytral margin and corresponding grooves on the hind femora. These modifications are not present in the other species in the genus, thus sound production in the adult appears to be an autapomorphy of this species that may be related to the larger size and threat display behavior.