Asian hornet nests change dramatically over the course of a single season, starting as small, inconspicuous structures in spring and growing into large secondary nests that can house thousands of hornets by late summer. Understanding what these nests look like, where they appear, and how they develop helps you identify one early, when removal is far easier and safer.
Primary Nests in Spring
A single queen that survived the winter builds the first nest, called a primary nest, starting in early spring. These nests are small, roughly the size of a tennis ball or golf ball, and made from chewed wood pulp that dries into a papery, grey-brown shell. The queen uses this nest to lay her first batch of eggs and raise the initial group of workers on her own.
About 77% of primary nests are found in man-made structures: garden sheds, garages, wall cavities, under eaves, in attics, or beneath decking. The queen tends to choose sheltered, low spots that offer protection from wind and rain. Because the nests are small and often tucked away, they’re easy to miss entirely during this stage. A primary nest typically holds just the queen and a handful of workers, so it poses relatively little danger compared to what comes next.
The Move to Secondary Nests
By late July, the growing colony abandons the primary nest and constructs a much larger, permanent secondary nest. This is the nest most people picture when they think of Asian hornets: a roughly spherical or oval structure made of the same layered paper material, but significantly bigger. Mature secondary nests can reach 60 to 80 centimeters across (roughly the size of a basketball or larger) and house several thousand individual hornets at peak population in late summer and early autumn.
The location shift is striking. While primary nests favor low, sheltered spots in buildings, about 74% of secondary nests are built high up in trees. Oaks and pines are the most common host trees, followed by plane trees, alder, cedar, and tulip trees. Another 22% of secondary nests still end up on man-made structures, and about 5% appear in other natural locations like hedgerows or cliff faces. Secondary nests are often 10 meters or more off the ground, which makes them nearly invisible during summer when tree canopy is full. Many are only spotted in autumn once leaves drop.
How to Identify an Asian Hornet Nest
Asian hornet nests look similar to the nests of native hornets and wasps at first glance, but there are key differences. The secondary nest has a single entry hole, usually on the side rather than at the bottom. The exterior is a mottled brown or grey color with a rough, papery texture formed by overlapping layers of chewed wood fiber. Native European or American hornet nests tend to have the opening at the base and are often more elongated or teardrop-shaped.
If you spot a large, roughly round nest high in a tree with heavy hornet traffic around it during August through November, there’s a reasonable chance it belongs to Asian hornets. Look at the hornets themselves for confirmation: Asian hornets (Vespa velutina) have a mostly dark brown or black body with a distinctive orange-yellow band on the fourth abdominal segment, orange face, and yellow-tipped legs. They’re slightly smaller than the European hornet but noticeably larger than common wasps.
Why These Nests Matter for Pollinators
A single Asian hornet nest poses a serious threat to local honeybee colonies and other pollinators. Asian hornets are aggressive predators of honeybees, hovering outside hive entrances and picking off returning foragers one by one. A group of hornets can decimate an entire bee colony in just a few hours during a coordinated attack. After such an attack, virtually 100% of the adult bee population is killed, with dead bees covering the ground outside the hive entrance. The hornets then remain in the conquered colony for up to a week, feeding on brood and honey stores.
Beyond direct predation, the persistent presence of hornets near a beehive causes bees to stop foraging. Colonies that aren’t outright destroyed can still weaken and collapse because they can’t gather enough food. This cascading effect on pollination is a primary reason governments in Europe and North America treat Asian hornets as a high-priority invasive species. Each nest destroyed before autumn prevents the release of new queens that would establish dozens more colonies the following spring.
Defensive Behavior Near the Nest
Asian hornets are not particularly aggressive toward humans when foraging away from their nest. Near the nest, the situation changes considerably. They will defend their colony, and what makes them more dangerous than many other hornet species is their tendency to attack as a group, recruiting other colony members to join the defense. A sting from a single Asian hornet is painful but comparable to a wasp sting for most people. Multiple stings from a coordinated defensive response carry greater risk, particularly for anyone with insect venom allergies.
If you discover a nest, the safest approach is to leave the area calmly without disturbing it. Avoid sudden movements, loud noises, or vibrations near the nest. Do not attempt to knock it down, spray it, or burn it yourself. A secondary nest with thousands of hornets inside will produce an aggressive swarm response that can be genuinely dangerous.
What to Do If You Find a Nest
Reporting a suspected Asian hornet nest to the appropriate authority is the single most useful thing you can do. In the UK, the preferred reporting method is the Asian Hornet Watch app, which allows you to upload a photo and location directly to the National Bee Unit. In the US, Washington State operates a dedicated reporting system: you can use the online Hornet Watch Report Form, email hornets@agr.wa.gov, or call 1-800-443-6684. If you’re outside Washington State, contact your state or province’s apiary inspector.
When filing a report, include as much detail as possible: your location, the date, a photograph of the nest or hornets (officials generally cannot confirm a report without a photo or physical specimen), and the direction the hornets were flying when they left. If you can’t get a photo, describe the size, coloring, and behavior of the insects. This information helps authorities locate and confirm the nest quickly.
Removal of confirmed Asian hornet nests is handled by trained professionals, typically at no cost when the species is part of an official eradication program. Removal usually happens at dawn or dusk when most hornets are inside the nest. The process involves injecting insecticide directly into the nest, then removing the physical structure once activity has stopped. For nests high in trees, specialists use rope-access techniques or elevated platforms. Early-season primary nests are far simpler to deal with, which is why spring identification and reporting are so valuable.