From BERLIN (Reuters) - German biologists have discovered a new species of ant they believe is the oldest on the planet, dating back around 120 million years.

Researchers from Karlsruhe's Natural History Museum found the 3-millimeter-long (0.118 inch) insect in the Amazon rainforest in 2007, and hope it will shed light on the early evolution of ants.

"It's by far the most spectacular find of my 26-year career," said museum biologist Manfred Verhaagh on Tuesday.

Scientists from Karlsruhe originally found an unidentified species of ant of a similar type in the Brazilian rainforest in 2003. However, due to an accident in the laboratory, the insect dried up, making further research impossible, Verhaagh said.

Last year a separate team from the museum's research body was in the forest investigating fungus when they stumbled upon the tiny insect, and named it "Martialis heureka".

Resembling a miniature wasp, the insect is like no other ant, and probably dates back 120 million years, making it the oldest still inhabiting the earth, Verhaagh said. The scientists used DNA samples from its front leg to establish its likely age.

The last discovery of a new ant species was in 1923, he added.