A Horta, guarding her eggs.

Horta anatomy was composed of a material similar to fibrous asbestos. They fed on rock, and thus they were nourished just by tunneling. Horta tunneled through rock like most humanoids walked through air, moving with the aid of an extremely corrosive acid. They left perfectly round tunnels in their wake. The Horta species possessed an unusually long life span. Every fifty thousand years, all of the Horta died out except for one, the so-called mother Horta, who then watched the eggs until they hatched, and mothered and protected them. Horta eggs were spherical in shape, and they seemed to mostly consist of silicon, aside from a few trace elements.