Rhinoceros Beetles are noted for the long horns present in male beetles. The horns are used for defending territory and a male with a longer horn can usually best a male with a shorter horn and thus be more likely to mate with a female. This correlation between long horn size and mating success selects for males with long horns. However, there is a limit to horn size. Horns that are too large must have some negative effects that oppose the selection for large horn size.A group from Montana tested the hypothesis* that males with larger horns might have more difficulty flying. The horn looks cumbersome and the extra weight of a larger horn could affect flight. However, when the flight characteristics of beetles with larger horns were compared to beetles with smaller horns or females with no horns, the data showed that the size of the horn had no appreciable effect on either flight distance or flight speed. Beetles with large horns can fully compensate for horn size through increase in strength of the wing muscles.This study eliminates impediment to flying as a limit to horn size. The search for limits to horn size must concentrate on factors other than flight.
*Behavioral Ecology, April 2012, doi:10.1093/beheco/ars069