Inexpensive load carrying by rhinoceros beetles

Abstract

These experiments determined the magnitude of loads that rhinoceros beetles (Scarabaeidae) can carry and also the metabolic energy required for carrying loads. I hypothesized that, like many other animals, these beetles would have metabolic rates in direct proportion to the total load (body mass plus added mass). Eight beetles (Xylorctes thestalus) walked at 1 cm s-1 on a motorized treadmill enclosed in a respirometer. The beetles could sustain this speed with loads of more than 30 times their body mass. In addition to being strong, these beetles carry loads with remarkable economy. The metabolic cost of moving a gram of additional load was more than five times cheaper than that of moving a gram of body mass. This phenomenon cannot be explained by conventional models that link the biomechanics and metabolic energy cost of locomotion.