German cockroach (Blattella germanica)
Measuring just about 1cm in length, German cockroches are one of three cockroach species considered pests in Singapore.
Unlike the Australian and American cockroaches, they do not fly. But they are carried by human transportation systems and adapt well to urban environments.
Ironically, clean, modern transporation systems have made it easier for German cockroaches to be carried around as there are fewer rats - its natural predator - around.
Australian cockroach (Periplaneta australasiae)
The Australian cockroach is about twice the size of the German cockroach, with a length of between 2 and 3cm. The Australian cockroach looks similar to the American cockroach, just slightly smaller and with yellow streaks by the sides of its body.
This cockroach can be found in Singapore's forests, where it helps to break down organic matter such as dead leaves.
This process is important as it means some of the nutrients in them are released back into the soil, where they can be used by other living things such as trees.
This cockroach speeds up this process of nutrient cycling, as the breakdown of dead matter by fungi and bacteria is much slower.
Madagascar cockroach (Gromphadorhina portentosa)
Measuring up to 7.5cm long, this cockroach is not considered a pest and is sometimes even kept as a pet. Its exoskeleton has an iridescent sheen, and this insect is known to hiss - as part of its mating ritual, or during fights.
Source: Dr Tang Qian, Foo Maosheng, National Geographic