The Kalahari Desert’s subterranean Damaraland mole-rat lives in an ensocial organization — a social structure similar to that of ants, but unique among mammals, the London Telegraph reported Thursday.

University of Pretoria researchers Michael Scantlebury, Nigel Bennett and colleagues say some of the mole-rats are industrious, while others are fat and lazy.

The industrious mole-rats are active year-round, while the lazy, infrequent workers spend much of their time resting.

The scientists suspect the lazy mole-rats are on standby to invade new territories or to search for food during lean times. In other words, they told The Telegraph, the lazier animals help ensure the long-term survival of the colony’s gene pool.

Scantlebury said: One way to think about this is to imagine the infrequent workers are like older teenagers. They do nothing around the house and they eat all your food. Yet you tolerate them because they are your only way to spread your genes into the wider world.

The study is reported in the journal Nature.