Hornets first appear in spring when overwintering queens emerge from hibernation, typically between April and May depending on your climate. Activity builds through summer, peaks in September, and ends with the first hard frost. The timeline varies by species and region, but the broad pattern is the same: a single queen starts a colony in spring, workers multiply through summer, and the whole colony dies off in fall except for newly mated queens.
Spring: Queens Emerge and Build Alone
The hornet season begins when a fertilized queen leaves her winter shelter. These queens spent the cold months tucked inside hollow trees, rock piles, under bark, or in the walls and attics of buildings. Once temperatures warm consistently in spring, they wake up and immediately begin building a small starter nest, laying the first batch of eggs, and raising the initial workers entirely on their own.
In southern states, this can happen as early as late March or April. In northern regions, queens may not emerge until May. The timing depends on local temperatures rather than a fixed calendar date. During this early phase, you’re unlikely to notice hornets at all. There’s only one queen per nest, and she stays close to the colony site while she raises her first generation of workers.
Summer: Colonies Grow Fast
Once the first workers mature, the colony shifts into rapid growth. From June through August, workers take over foraging, nest construction, and larva care while the queen focuses solely on laying eggs. This is when you start seeing hornets regularly around your yard, garden, and outdoor food.
Baldfaced hornets, the black-and-white species common across North America, can grow their colonies to 100 to 400 workers over the summer. European hornets, the only true hornet species in North America (an accidentally introduced species, according to Penn State Extension), follow a similar growth curve. Their nests peak later, in mid-September, when most contain 200 to 400 workers, though large nests can reach up to 1,000.
During summer, workers are busy hunting insects to feed developing larvae. They’re focused on protein at this stage, catching caterpillars, flies, and other prey. You’ll see them most often during daylight hours, though European hornets are notably active at night and are attracted to porch lights and windows after dark.
Late Summer and Fall: Peak Aggression
August through September is when hornets become most noticeable and most likely to bother you. Two things change at once. First, the colony is at or near its maximum size, meaning far more workers are out foraging. Second, the colony’s dietary needs shift. As fewer larvae remain to feed, workers stop hunting insects for protein and start craving sugar instead. They’ll seek out overripe fruit like apples and figs, sodas, juice, and anything sweet at your outdoor meal.
This sugar-seeking behavior is why hornets and their close relatives seem to appear out of nowhere at barbecues and picnics in late summer. They aren’t more aggressive in a territorial sense. They’re just hungrier for carbohydrates and more numerous than at any other point in the year. That said, a larger colony also means a more vigorous defense if you accidentally disturb a nest.
Fall: New Queens and Colony Death
As fall approaches, the colony produces its final generation: new queens and males. These leave the nest to mate. The newly fertilized queens then find a sheltered spot to spend the winter. Everything else in the colony, the old queen, all the workers, and the males, dies before or shortly after the first hard frost.
This means old nests are never reused. Each spring, every queen starts the nest-building process over completely from scratch. If you find a papery hornet nest in winter, it’s abandoned and won’t be repopulated. The queens overwintering nearby will build entirely new nests in a different location come spring.
Daily Activity Patterns
Within the active season, hornets follow a daily rhythm tied to light and temperature. Most species are daytime foragers, becoming active after morning temperatures warm up and returning to the nest at dusk. You’ll see the most activity on warm, sunny afternoons.
European hornets are the notable exception. They fly at night and are regularly drawn to artificial lights. If you see a large, brownish-yellow hornet buzzing around your porch light on a summer evening, it’s almost certainly a European hornet. This nocturnal foraging habit makes them unique among social wasps in North America.
What Climate Means for Your Timeline
Your local climate compresses or stretches the entire hornet calendar. In the Deep South, queens may emerge in March and colonies can remain active into November. In the upper Midwest or New England, the season runs roughly May through October, with a hard frost ending things earlier. Mild winters can also mean queens emerge sooner in spring, giving colonies a longer growing season and potentially larger final populations. Conversely, a late spring frost after queens have already emerged can kill them before nests get established, leading to fewer hornets that summer.