Probability of mounting a male by mistake and the probability of being mounted by a male. Probabilities were calculated assuming males use the decision rule ‘mount individuals larger than me’. Data were from sizes of 2,685 females and 4,142 males measured for a previous study (Switzer et al. ). For both of these probabilities, we assumed that the single individuals are a random sample from the population with respect to size. The probability of making a mistake was calculated by using the male and female cumulative frequencies (i.e., percentage of males and females that were larger than a male of a given size) and the overall sex ratio of single individuals (i.e., 70% male). The probability of being mounted was calculated by multiplying the probability of making a mistake for each size class of male by the proportion of males in that size class, and then summing those values for all males smaller than the size of the male of interest. Mean male size for this sample was 5.82 ± 0.005 mm (denoted by the arrow in the figure); mean female size was 6.26 ± 0.007 mm.