The Madagascar Hissing Cockroach (Gromphadorhina portentosa) is a large, wingless insect native to Madagascar, often kept as an exotic pet due to its size and unique sound-making ability. Determining the sex of this species is important for controlled breeding or managing a colony’s population size. The differences between males and females influence their appearance, behavior, and reproductive roles.
Identifying Physical Differences
The most immediate way to distinguish the sexes is by examining the pronotal tubercles, which are large, horn-like projections located on the shield-like segment behind the head. Males possess prominent, well-developed tubercles, sometimes giving the impression of horns. Conversely, females have significantly smaller, less noticeable bumps or are almost smooth in this area.
Another method for sexing involves looking at the terminal abdominal segments from the underside. In males, the last ventral plate (sternite) is often divided into smaller, segmented plates. The female’s last abdominal segment is generally larger, smoother, and consists of a single, broad plate. Additionally, males tend to have slightly thicker, hairier antennae compared to the females’ smoother, thinner antennae.
Distinct Behavioral Roles
The differences in morphology lead directly to distinct social behaviors, particularly regarding dominance and communication. Both sexes, as well as nymphs, can produce a loud disturbance hiss by forcibly expelling air through modified spiracles when they are startled or threatened. However, only males utilize additional, more complex hisses for social interaction.
Males produce a fighting hiss during aggressive encounters and a courtship hiss to attract a female before mating. The fighting hiss conveys information about the male’s size, helping competitors assess one another. Male-male aggression is common as they establish and defend territories containing resources or females.
During territorial disputes, males actively use their pronounced pronotal tubercles to push rivals, much like horned mammals. The larger male, who demonstrates aggressive posturing such as standing on his “toes” (stilting), usually wins the encounter. Females and nymphs are generally more social and do not engage in these territorial battles.
Reproductive Functions
Once mated, the female takes responsibility for incubation and birth. She is ovoviviparous, meaning she produces an ootheca (egg case) but carries it internally within a specialized abdominal brood pouch. The eggs develop and hatch inside her body, a process that usually takes around 60 days.
The female gives birth to live young, pushing out fully formed nymphs. A single gestation results in a brood of approximately 15 to 60 nymphs, though two to three dozen is more common. Neither parent provides post-birth parental care to the nymphs. The female is capable of producing multiple broods a year if conditions remain warm.