Pokémon belonging to the Bug Egg Group are unique in several distinct ways. First off, most of them are insectoid or bug-like in appearance and share most of their characteristics with the identically named Bug-type. However, they also contain arthropod-like critters making them quite diverse.
When it comes to breeding or chain breeding, one quickly realizes that this Egg Group aggravates the process of move inheritance dramatically, as most base-level Bug-type Pokémon are unable to learn moves by breeding. This inability to inherit moves is due to many base-level Bug-type Pokémon not being part of another Egg Group. To somewhat compensate for this drawback, many possess unique ways of evolution like Nincada.