Are European Hornets Aggressive? Behavior and Real Sting Risk

Why do hornets have such a fierce reputation?

The European hornet is the largest social wasp in Europe, with queens up to 35 mm (1.4 in) long, and its loud, deep buzz makes it sound threatening. Old sayings add to the fear. A well-known one claims that three hornet stings can kill a person and seven a horse, which has no basis at all.

In reality, entomologists and hornet conservationists describe European hornets as peaceful insects that avoid conflict whenever they can. Their size and color are a warning, not a sign of bad temper. Much of their bad reputation comes from confusion with other insects, including late-summer wasps and, more recently, the giant hornets of Asia.

How do hornets behave away from the nest?

A European hornet out hunting or feeding is busy and uninterested in people. Adults spend their time drinking tree sap, sipping juice from fallen fruit and catching insects for their larvae. When a person comes close, a hornet usually flies away or simply carries on feeding.

European hornets come to tables for jam, cake or soft drinks far less often than common wasps and yellowjackets do. If they do visit outdoor tables or fruit trees in late summer, they are often hunting the wasps and flies gathered there. This is one reason why many people find hornets less of a nuisance than ordinary wasps; see why wasps get aggressive in late summer.

Problems away from the nest usually come from accidental contact. A hornet can sting if it is squeezed in a hand, trapped inside a sleeve, stepped on barefoot, or picked up with a piece of fallen fruit. Swatting at a hornet in flight makes a sting more likely, while keeping still or moving away calmly makes it less likely.

When do European hornets sting?

The nest is where hornets become defensive. Like all social wasps, a colony protects its queen, its brood and its food, and guards watch the area around the entrance. Most colonies defend a zone of about 2–6 m (7–20 ft) around the nest. Things that commonly trigger a defense include:

• standing in the flight path in front of the entrance
• shaking, knocking or vibrating the nest tree, wall or bird box, for example with a lawn mower or hedge trimmer
• breathing on hornets at the entrance or poking the nest
• repeated disturbance, which makes a colony more defensive over time

When a guard senses a threat, it releases an alarm pheromone from its venom sac that calls more defenders, so one sting near a nest can be followed by more. Colonies are largest and most defensive in August and September, when they may hold a few hundred hornets.

Hornets indoors at night

European hornets are among the few social wasps that fly at dusk and on warm nights, and they are attracted to lit windows. A hornet buzzing around a lamp at 10 p.m. can be alarming, but it is lost and dazzled, not attacking. Most indoor stings happen when someone grabs or steps on a hornet by accident. Turning off the indoor light and opening the window usually lets it find its way out. Read more in Do hornets fly at night?.

How does a hornet sting compare with a bee or wasp sting?

Hornets, wasps and bees all sting with a modified egg-laying tube, so only females can sting. Hornets and wasps have smooth stingers and can sting repeatedly, while a worker honey bee’s barbed stinger usually stays in the skin; see do bees die after they sting? and can a wasp sting more than once?.

Hornet venom contains acetylcholine, a substance that intensifies pain, so many people find a hornet sting hurts a little more than a wasp sting. Yet laboratory tests on mice suggest that, gram for gram, European hornet venom is weaker than honey bee venom. Hornets and wasps also tend to inject less venom per sting than a honey bee, whose detached stinger keeps pumping venom into the skin.

Is a hornet sting dangerous?

For a healthy adult who is not allergic, a sting from a European hornet causes pain, redness and swelling that usually fade within a few days. A few stings are painful but not life-threatening, and the “three stings kill” saying is a myth.

The real danger, as with bees and wasps, is allergy. Hornet venom shares most of its allergens with wasp venom, so people who react badly to wasp stings usually react to hornet stings too. A severe allergic reaction can start within minutes of a single sting. Anyone who has trouble breathing, feels faint, or develops swelling of the face, lips or throat after a sting should seek emergency medical help immediately by calling 911 in the US, 112 in the EU or 999 in the UK.

The simplest way to avoid stings is to respect the hornet’s space: watch hornets from a few meters away, keep clear of nest entrances, and never swat at a hornet in flight.