Onymacris rugatipennis is one of several diurnal adesmiine tenebrionid beetles living in various habitats near Gobabeb in the Namib Desert, South West Africa.
Late in the active part of the female daily cycle and before they dig into the ground, females are often persistently followed by one or more males. Intruding male challenges to followers are commonplace. Following occurs during the latter phase of the morning and especially during the afternoon activity cycle. Early in these activity cycles the principle male activity is feeding. Males emerge in the morning earlier than females, and late in their activity period most males are engaged in following or attempts to dislodge other followers. Of the five diurnal adesmiine species living near Gobabeb, only the males of O. rugatipennis fight with one another and defend space. Their space is maintained above the site where a female has dug into the ground at midday or in the evening. Defense involves exclusion of other males from the immediate vicinity of the female. Alien males are immediately evicted, but on some occasions there are serious challenges. Pairs of males may engage in vigorous wrestling matches involving head butting, shoving, throwing, biting, and kicking. Evenly matched individuals may wrestle for over 30 min and for more than 20 falls. The winner of such encounters remains over the buried female. The last individual to hold the space in the evening may mate with the resident female. The observed behavior is not territorial in the sense that there are no mutually recognized frontiers. There is, however, exclusive use of space and aggressive defense of that space.
Social order is re-established daily. There are no persistent inter-individual bonds between males and females. Males may return to the general area but not the exact place where they held space the previous day. Many individuals move long distances from the place where they were active on the preceding day.
Larger males tend to win wrestling matches. However, males are on the average smaller than females. Since larval males live in the habitats occupied by females, adult male body size is apparently not limited by larval energy limits. Hence we conclude that small adult male body size conveys advantages which may outweigh the disadvantage in wrestling matches. Some of the possible selection relationships countering large male size are discussed.
Females reject most mating attempts by males when they are active on the surface. They exercise no choice in mate selection following burrowing. Hence the mating system results in mating by the most persistent male followers and aggressive individuals able to hold the space above the place where the female burrows into the ground.