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 two hours 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 hours 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.