The Tetraps have four eyes, one on each side of their head which allows them to see in all directions. Like bats do, the Tetraps sleep upside down in a cavern. To feed the Lakertyan leader releases a dark red-coloured sludge down a chute into a trough.
Tetraps are not the most cleverest of creatures but they soon realise that The Rani's plans would have them all killed on Lakertya. They find this out when their leader, Urak, hears of her plans and she later leaves him to guard over her laboratory rather than take him with her in her Tardis (leaving him to die). Urak and the rest of the Tetraps, enraged, capture the Rani in her ship and take her back to their home planet, to force her to solve their natural resource shortages.