Modern ants are social insects with a fascinating and complex societal structure. These hardworking insects appear down-to-earth - because they literally are - and seem so cooperative with each other that you wouldn't think they would have had violent tendencies.

Surprisingly, they do. Like human groups, prehistoric colonies of ants have fought with each other over territory and food.

The only difference, however, is that ants have begun fighting long before humans did: at least 100 million years ago.

Fossil insect expert Phillip Barden of Rutgers University-Newark says many ant species fight all the time.

"They're always warring with either other individuals of the same species from different colonies or with different species," says Barden.

The "Ant Wars" started during the Cretaceous period, when large dinosaurs roamed the Earth. Barden says the species of ants trapped in ancient Burmese amber are among the earliest species of ants.

Barden, the lead author of the study, adds that these ancient ants belong to lineages significantly different from modern ants. These ancient ants are not direct ancestors of living ants today, but they do have their own branch.

Aside from that, ancient ants were also social insects, he says. This is evident in a piece of amber that the research team currently holds. The amber contains as many as 21 worker ants trapped in it.

"That's significant because at this time period, ants are very rare to find in fossils," said Barden. Ancient ants comprise less than 1 percent of all insects in amber, so finding about 20 ants in one piece suggests social behavior.

Scientists have identified 13,000 species of living ants today. Some experts believe that at least 26,000 species exist, and that several modern ant species are related to the ancient ones that lived 99 million years ago.

Ants have done so well as a result of their social behavior. Instead of fighting as one individual, ants form large groups that reach tens of thousands and even millions to fight other colonies. Most ants are not reproducing but work hard for the colony. Researchers said this is a beneficial trait.

The study, which Barden co-authored with David A. Grimaldi of Cornell University, is featured in the journal Current Biology.