Lifting Capacity of Horned Passalus Beetles During Passive and Stressed States

Abstract

Many beetle species engage in territorial behaviors or male-male contests involving lifting or flipping their opponents, although this type of strength has never been empirically quantified. This study examined the lifting capacity of a medium-sized (1–2 g) saprolytic beetle native to the United States (horned passalus beetle, Odontotaenius disjunctus), and strength was measured during passive and stressed states. Twenty beetles were individually placed in a ‘push-up’ position with a force sensor on their backs and allowed to lift continuously for 2 min without manipulation, and then for another 2 min with a mild stress stimulus applied (tapping the elytra with a probe). The unmanipulated peak force readings during the first half were surprisingly high (up to 5 N, or 500 g), based on prior experiments examining the pulling strength of this species (indicating they can pull up to 100 g), but in nearly all beetles their peak lifting power in the stressed state increased by an average of 87 %. There was a positive relationship between strength measurements in both passive and stressed states. This appears to be the first empirical demonstration of the lifting capacity of a beetle, and these results also have considerable implications for the study of physical performance in beetles and other animals, especially in cases where maximum exertion data are of interest.