Samurai wasp ovipositing on brown marmorated stink bug eggs (photo from Wikimedia Commons)

16 October 2025

Remember the brown marmorated stink bug invasion? Halyomorpha halys was first noticed in Allentown PA in 1998 and soon spread across the state. By 2010 alien stink bugs were causing record damage in Pennsylvania orchards and annoying homeowners by invading tiny cracks in our homes at the first sign of cold weather. October used to be the worst month for this.

Brown marmorated stink bug outside my window, August 2023 (photo by Kate St. John)

Studies back then predicted where the stink bug was likely to invade while USDA searched for a biological control. They were looking for a predator within the brown marmorated stink bug’s native range that would not pose a threat to North American species.

Meanwhile the stink bug continued to spread. By within 20 years it was thick in the I-95 Corridor, clearly established east of the Mississippi, and had spread in the Pacific coast states.

Distribution of brown marmorated stink bug in the U.S. 2000 to 2019 (animation from Wikimedia Commons)

By 2018 researchers had settled on a safe non-stinging wasp, the Samurai wasp (Trissolcus japonicus), that lays its eggs inside brown marmorated stink bug eggs; its larva eats the egg from within. The map below shows the wasp’s potential range around the world. Its outlook as a solution in the eastern U.S. was great but it was marginal to unsuitable in the West.

Approvals to import the wasp were still grinding through the bureaucratic process when the Samurai wasp showed up on its own as described in this vintage article: Stinkbug Predator Shows Up On Its Own.

As soon as that happened the wasp became available to farmers in need of stink bug control and the wasp continued to spread on its own.

By 2021 it had spread to North Carolina and surprisingly to southwestern Idaho, a place that was mapped (above) as marginal to unsuitable habitat for the wasp.

By the wasp doesn’t care. There are stink bugs in Idaho so the wasp flew eastward from Oregon found a new home. This USDA map on the stopbmsb.org website shows the distribution of both species, the stink bug in solid colors, the wasp as dots.

USDA map of brown marmorated stink bug and Samurai wasp distribution via stopbmsb.org

Back here in Pennsylvania the brown marmorated stink bug is rarely seen anymore, thanks to the female Samurai wasp who’s a great traveler in search for prey on which to lay her eggs.

p.s. I wonder how she finds the stink bugs. Can she smell them from afar?