Contrary to popular belief, 20 percent of worker ants are not particularly hardworking, researchers said Saturday.

The discovery is the result of observations of three separate 30-strong colonies of black Japanese ants (Myrmecina nipponica), according to Eisuke Hasegawa, an assistant researcher in evolutionary biology at Hokkaido University’s graduate school of agriculture, and his research team.

The team transferred three colonies of ants to a man-made nest and marked them for observation. Hasegawa and his team said they observed the ants three hours a day for about five months from May last year.

Hasegawa said they discovered that about 80 percent of the ants engage in some sort of work, such as cleaning the nest or gathering food, but that the rest are mostly idle.

The situation remained the same when the researchers removed six busy ants from one colony; the busy ants that remained had to work even harder while the lazy ants continued to do little or no work.

Scientists have suggested that some ants may avoid working due to old age or inherent laziness. Hasegawa said the idle ants could be contributing something to the colony that they have not yet determined.