Bug

Insects, spiders, centipedes and caterpillars: 85 of its 91 species are Bug type. Burmy shows how much gender matters here: a female evolves into Wormadam, which is always female, and a male into Mothim, which is always male.

The Bug egg group has 91 species, 72 of which belong to this group alone. The groups it shares the most species with are Water 1, with 4, and Water 3, with 4. Between them they can breed with 503 different species, Ditto included. All of them can breed with Ditto, and all of them have a gender. Of these, 2 are always male and 3 always female, and two of the same gender cannot breed with each other even if they share a group.