Amber, or fossil tree resin, exists in rock layers all over the world. But for some reason, paleontologists never found much of it in Australia or New Zealand.

That’s why it was exciting when Jeffrey Stilwell, a paleontologist at Monash University in Melbourne, and a group of students, found a stash in southern Australia in 2011. The find led Dr. Stilwell to mount a search for more amber at sites across Australia and New Zealand, with one of the specimens more unusual than all the rest: It contained two insects frozen in the act of mating.

“I looked at the piece under the microscope, and when I looked at it, I said, ‘This looks really important, because it looks like they’re almost attached or something,’” he said. “I couldn’t believe it — it looks like they’re mating.”

Dr. Stilwell and his colleagues detailed their findings in a paper published Thursday in Scientific Reports.