Do Hornets Fly at Night? Why European Hornets Hunt After Dark

How late do hornets fly?

The European hornet is a daytime insect that simply does not stop when the sun goes down. Hornet watchers have long noticed workers returning to the nest in near darkness, and two studies measured it.

In 1958 the entomologist R. E. Blackith compared the first and last flights of the day for hornets and three species of smaller Vespula wasps. The hornets started earlier in the morning and stopped later in the evening, at light levels about 100 times lower than the smaller wasps needed. He concluded that hornets should be able to fly on nights with a full or three-quarter moon.

A 2011 study led by Almut Kelber at Lund University filmed a hornet nest in southern Sweden over several days and nights in August. Traffic at the entrance was steady from about an hour before sunrise to an hour after sunset, then fell off as the light faded. On nights with little moonlight, hornets kept flying a little beyond the end of civil twilight, the time when the sun is 6 degrees below the horizon, but not as late as the end of nautical twilight, when the sun is 12 degrees below the horizon.

So hornets are best described as facultatively nocturnal: they are mainly active by day but can extend their working day into the night when there is enough light.

How can hornets see in the dark?

Truly nocturnal bees and wasps have special eyes. The night-flying Megalopta sweat bees and Apoica paper wasps of tropical America have enlarged ocelli, the three small simple eyes on top of the head, and compound eyes with unusually wide light-sensitive units called rhabdoms. These features make their eyes far more sensitive to light.

The Lund team expected to find similar adaptations in hornets, but they did not. When they compared hornet eyes with those of the common wasp, they found that hornet eyes were, if anything, slightly less sensitive. The hornet’s advantage is its size. A hornet worker’s head is nearly twice as wide as a common wasp’s, so its eyes are bigger, with larger facet lenses that gather more light.

The researchers suggested that hornets may also pool signals from neighboring parts of the eye in the brain, trading sharp detail for extra sensitivity, as some large bees are thought to do. Even so, dim light slows hornets down: an earlier experiment found that tethered hornet workers flew more slowly in dim light than in bright light.

What do hornets do after dark?

Most of a hornet’s evening is spent finishing its daytime work. Workers carry the last loads of chewed insects to the larvae, bring in wood pulp for building, and return from feeding on tree sap and fallen fruit. A longer working day lets a colony gather more food during the short northern summer.

European hornets catch a wide range of insects, including moths, and lamps that attract moths may also attract hunting hornets. It is often said that hornets visit lights to hunt moths, but this has not been well studied, and many hornets at windows seem simply confused by the light.

Why are hornets attracted to light?

Many night-flying insects, from moths to beetles, are drawn to artificial light, and hornets are no exception. Bright lamps appear to disrupt the way flying insects keep their bearings, so they circle or crash into the light instead of flying on.

For people, this explains the classic late-summer surprise of a large hornet buzzing around a ceiling light or bumping against a window at night. The hornet is lost, not hunting people, and it will usually sting only if someone grabs it or steps on it. Turning off the indoor light and opening the window usually lets it find its way out. For more on how hornets behave around people, see Are European hornets aggressive?.

Do other wasps and hornets fly at night?

Most social wasps are strictly daytime insects. Common wasps and German wasps stop flying in the brighter part of dusk and spend the night in the nest. The invasive Asian hornet in Europe also hunts mainly in daylight, with peaks of activity in the morning and afternoon.

A few wasps have gone further than the European hornet and become fully nocturnal:

Being active at night brings advantages, such as fewer predators and less competition, but it needs more sensitive eyes. The European hornet shows that a large body can be enough to make a start without special night vision. Other animals that have taken up a night-time lifestyle are covered in nocturnal animals.

When are hornets most likely to fly at night?

Night flights are most noticeable in late summer and early autumn, from about August to September, when hornet colonies are at their largest and there are many workers out foraging. Warm, still evenings and bright moonlight help, while cold or rainy nights keep hornets at home. Lit windows and outdoor lamps draw them in, which is why so many people meet hornets around houses after dark.