An invasive hornet takes hold around the Sonian Forest

Confirmed, established populations of the Yellow-legged Hornet are turning up in and around the Sonian Forest on the edge of Brussels.¹ Nineteen research-grade records came back from this stretch of the European Atlantic mixed forests ecoregion, running from late February through the first week of August and clustered across Watermael-Boitsfort, Auderghem, Woluwe and Groenendael on the Hoeilaart side of the forest. Two of them are identified all the way to Vespa velutina nigrithorax, the subspecies behind the European invasion. Every record is flagged introduced. That matters more here than it might elsewhere, in a forest that carries legal protection precisely because of the species that depend on it.

This hornet is a different kind of concern from the seasonal sightings that usually fill a summer field note. It is not native to Europe, and the pattern here — repeat sightings at the same handful of sites, spanning most of a season rather than a single week — is what distinguishes a spreading population from a stray individual. It hunts. Workers station themselves outside honeybee hives and native bee nests, snatching foragers returning heavy with pollen, sometimes hovering at the entrance long enough over a season to strip a colony of its workforce. Native wasps and bees, which evolved without this predator in the picture, have no particular defense against it. A protected forest is exactly the kind of place where sustained predation pressure on pollinators carries the highest stakes.

This is a presence record, not a population count. Observation counts reflect observer effort, not abundance. What the records do establish is that the hornet is here and persisting across the season, not just passing through, which is the threshold that usually triggers nest-search and removal efforts in affected regions. Anyone spending time in the Sonian Forest this season is worth asking to keep an eye out and report sightings, since early nest detection is the main lever available against this species once it's established.