There are few insects that are as unwelcome in homes as cockroaches. Contaminating food with their feces and the disease-causing bacteria they carry on their bodies, these pests find a home they like, settle in and reproduce so quickly that getting rid of them can be difficult if not impossible. Entomologists have classified more than 4,000 species of cockroaches. In the US, the four species most often found are the German, American, Oriental and brown-banded cockroaches. So how do cockroaches reproduce?
As with many animals, cockroach reproduce sexually. This means that their reproduction relies on eggs from a female and sperm from a male. The female releases powerful pheromones to attract a male, and in many species, males fight over available females. But exactly what happens after the male deposits his sperm into the female varies from species to species.
Roaches are mostly oviparous — their young grow in eggs outside of the mother’s body. The mother roach carries her eggs around in an ootheca, or egg sack, which is attached to her abdomen. The number of eggs in each ootheca varies widely depending upon species. Many female roaches drop or hide their ootheca shortly before the eggs are ready to hatch, while others continue to carry the hatching eggs and care for their young after they are born. But regardless of how long the mother and her eggs stay together, the ootheca has to stay moist in order for the eggs to develop.
Do cockroaches always require a mate to reproduce? Not always. Scientists have found that in some instances, cockroaches can reproduce asexually. Parthenogenesis is a form of asexual reproduction, allowing young insects to spawn from unfertilized eggs.
It is the main mode of reproduction for some rarer cockroach species, and also can occur naturally in other invertebrates such as fish, amphibians, reptiles and even turkeys.
In the case of the American cockroach, the largest roach commonly found across the globe, parthenogenesis was, until recently, thought to be an option of last resort. But now we know that this phenomenon happens a lot more often than we thought.