The Mordellidae are a family of beetles commonly known as tumbling flower beetles for the typical irregular movements they make when escaping predators, or as pintail beetles due to their abdominal tip which aids them in performing these tumbling movements.[citation needed] Worldwide, there are about 1500 species.[1]
Anatomy
The apparent tumbling movements are composed of a series of very rapid separate jumps (each jump of a duration of approximately 80 ms). They result from the beetle's efforts to get itself back into take-off position for flight when it has been in either a lateral or dorsal position. Each individual jump should be considered an extended rotation, performed by one leg of the third leg pair (metapodium). Depending on whether the left or the right metapodium is used as the leg that provides the leverage for take-off, change occurs in the direction of the jump. The energy for propulsion varies with the beetle's immediate muscle work, so that jump lengths and heights vary, with rotation frequencies recorded up to 48 per second (Mordellochroa abdominalis) around the gravitation centre of the body's longitudinal axis. Additional revolving around the transverse axis (at lower frequency) effects spiralling somersaults that are perceived as tumbling. While the pintail (pygidium) is of no significance for the jump, the meta-trochanter-femur (thighs and surrounding rings of the third leg pair) has a great capacity for free rotation (up to 270 degrees, at one level only). This capacity is due to a screw joint that connects the base of the metacoxa to the head of trochanter. The nut gradient is 21 degrees. Technically similar jumps, though less powerful, can be observed in the families Melandryidae (=Serropalpidae) (genus Orchesia) and Scraptiidae (genus Anaspis). Their coxa-trochanter-joints are of similar structure. It is inferred that the capacity of a tumbling form of locomotion is rooted in a common phylogeny and can therefore not be ascribed specifically to Mordellidae.[2] Other authors have pointed out the speciality of the screw joint. Weevils of the genus Trigonopterus, in the Asian tropical rainforest, for example, have an even tighter connective construction in the coxa-trochanter joint than is found in Mordellidae. This construction, however, does not facilitate an equally high angular velocity of the torque. The joint here serves to provide a better grip on plants and easier climbing.[3]
^Michael A. Ivie (2002). "Mordellidae". In Ross H. Arnett & Michael Charles Thomas (ed.). Polyphaga: Scarabaeoidea through Curculionoidea. American Beetles. Vol. 2. CRC Press. ISBN978-0-8493-0954-0.
^Michael Reuter (1995). "Studies on the functional morphology of the jump in tumbling-flower beetles (Mordellidae, Coleoptera)". Acta Biologica Benrodis. 7: 99–133. ISSN0177-9214.
