The most common type of bed bug, and the species known to prefer human blood, is Cimex lectularius. Other species exist, but this one has adapted to human environments. Its preferred habitats are heated homes and properties where it can infest beds and sofas.
The species is most active at night, often hiding during the day - although it is not uncommon to find active bed bugs during daylight hours. For this reason they are not classed as strictly nocturnal.