Diglett is a tiny, brown Pokémon that seems to be perpetually buried within the earth, leaving only its head visible. It has beady black eyes and a large, round, pink nose. A Diglett in Pokémon Mystery Dungeon: Red Rescue Team and Blue Rescue Team mentions that it has feet, though their size and appearance are unknown. It spends much of its time underground, and has very thin skin. If Diglett is exposed to sunlight, its blood will heat up and cause it to grow weak.

Diglett digs regularly through the earth at a shallow depth, leaving perfectly tilled soil in its wake. Diglett lives in tunnels and caves under the earth, where it feeds on tree roots. It also sometimes lives in burrows near forests, and has even been shown to live inside of trees.