Scientists have found the oldest fossil depicting copulating insects in northeastern China, according to a study published Wednesday in the U.S. journal PLOS ONE.

Fossil records of mating insects are fairly sparse, and in the study, Dong Ren and colleagues at the Capital Normal University in China presented a fossil of a pair of copulating froghoppers, a type of small insect that hops from plant to plant much like tiny frogs.

The well-preserved fossil of these two froghoppers showed belly- to-belly mating position and depicts the male reproductive organ inserting into the female copulatory structure, the researchers said.

"We found these two very rare copulating froghoppers which provide a glimpse of interesting insect behavior and important data to understand their mating position and genitalia orientation during the Middle Jurassic," Ren said in a statement.

This is the earliest record of copulating insects to date, and suggests that froghoppers' genital symmetry and mating position have remained static for over 165 million years, they added.