Living with males leads to female physical injury in the leaf-footed cactus bug

Males in many species possess sexually selected weapons that they use to fight for mating opportunities. It is well established that male-male competition can lead to physical injuries for males. However, very few studies have looked at the physical consequences for conspecific females. We hypothesized that living with males in a species with male-male competition would result in female injury. Because larger female invertebrates typically have greater reproductive output, they have higher resource value for males and can elicit aggression and fighting. Thus, we further hypothesized that larger females in this context would receive more injuries. For this study, we focused on the leaf-footed cactus bug, Narnia femorata (Hemiptera: Coreidae), a species of insect in which males fight using their spiny and enlarged hindlegs. In just 2 h of observation, we documented males competing with other males in 61% of 103 trials. In 43% of these 63 competitions, females were physically contacted and sometimes attacked with a kick or squeeze. We left insects in social groups for 74 h and found that females living with multiple males had a higher likelihood of obtaining injuries (26.2% of 103 trials) compared to those living only with females (9.7% of 103 trials). In addition, larger females were more likely to be injured compared to smaller females. Our study highlights the harm that females can experience in species with male-male competition.