"Animals that are completely asexual are relatively rare, which makes this is a very interesting ant," says Christian Rabeling, an ecology, evolution and behaviour graduate student at The University of Texas at Austin.

"Asexual species don't mix their genes through recombination, so you expect harmful mutations to accumulate over time and for the species to go extinct more quickly than others."

"They don't generally persist for very long over evolutionary time."

Mycocepurus smithii is a common species of fungus-gardening ants, which is widely distributed throughout Latin America and relies on a symbiotic fungus for food.

Previous studies of the ants pointed toward the ants being completely asexual.

Anna Himler, a graduate student at The University of Texas at Austin, showed that the ants reproduced in the lab without males -- no amount of stress induced the production of males.

Formerly it was thought that specimens of male ants collected in Brazil in the 1960s were males of M. smithii.

Rabeling analysed these samples and determined that the males were in fact of the species Mycocepurus obsoletus, a closely related fungus-gardening ant that does reproduce sexually.

He also dissected reproducing M. smithii queens from Brazil -- their sperm storage organs were completely empty.

Rabeling and his colleagues estimate the ants could have first evolved within the last one to two million years -- a very young species given that the fungus-farming ants evolved 50 million years ago.

He is now using DNA analysis to study the evolution of the fungus-gardening ants.

It is hoped that this will determine a more accurate date for the change in M. smithii that led to them dispensing with males altogether.