Long before an ordinary chicken egg became an Instagram star, Jun Endo, a Ph.D. student at Kyoto University, sat gazing intently at another egg. This egg was much smaller, roughly the size of a sesame seed, and contained a stink bug.

The mystery was this: When the egg finally hatched, it would do so virtually in unison with all the other stink bug eggs clumped around it. How? What signaled an egg on one side of the brood to hatch so soon after an egg on the other side?

Synchronized hatching may be common in the animal world; scientist can’t say for sure, as the phenomenon is not well studied. Sometimes b ird eggs in the same clutch hatch individually, in a series that can unfold over more than a day . The broods of some stink bug species hatch over several hours.

Mr. Endo’s brood belonged to the brown marmorated stink bug, Halyomorpha halys, which is known for wreaking havoc on farms and in suburban homes across the United States. Through a series of experiments, he attempted to identify the cue that got the eggs hatching.