Hornets are pollinators and are fascinating insects, but they are no friend of the honey bee. Here, we'll take a look at the fascinating methods honey bees use to defend themselves against this dangerous enemy.
Eusocial hornets live in colonies of several hundred individuals, but unlike bees, they don’t rely on nectar and pollen for rearing their young. Instead, hornets feed their own young with other insects and their larvae.
Thus a honey bee colony of several thousand bees provides a lot of food for hungry hornets and their young.
This fact, coupled with the physical characteristics of a hornet: a venomous sting, larger size than the honey bee, a tough chitin exoskeleton to protect themselves against stings from bees, and large jaws (mandibles) for crushing and biting their target prey, mean that hornets are a deadly predator and a major threat to bees.
During mass attacks on hives, hornets can literally kill thousands of bees within a few hours.
Hornets employ a range of tactics in their attacks on honey bees.
In general, individual hornets may pick off single bees, or several hornets may embark on a full scale attack on the colony.
Single hornet attacks
Single hornets may attack bees by hunting them from the air, or ambushing bees whilst foraging. They may also target bees as they leave, approach or land at the nest entrance.
After catching a bee, the hornet flies off to a suitable perch where it can rest and manipulate the prey, biting off the head and sometimes other body parts (wings and legs), before flying off with the dismembered bee, partially chewed, back to its own nest where the carcass of the bee will be fed to the developing hornet larvae.
Mass hornet attacks
Some hornet species are known for deadly mass attacks on nests or hives, killing many bees and destroying colonies.
Vespa mandarinia (Asian giant hornet, also known as the 'Murder hornet') and Vespa soror (the Giant hornet) are two species especially known for such attacks.
When a single Vespa mandarinia or Vespa soror scout hornet locates a honey bee nest or hive, it chemically marks it by rubbing its abdomen on the surface, and then recruits fellow colony members to the site. To gain easier access to the hive or nest, they chew at the entrance, and kill any defending worker guard bees.
A group of 50 hornets can kill thousands of bees within a few hours, the surviving honey bees sometimes absconding from the hive.
The hornets then take up occupation of the nest, all the time guarding it whilst they begin a process of removing dead bees and larvae which the hornets carry back to their own nests to feed their offspring.
Honey bees have developed a number of ways to defend themselves against hornets, including physical, chemical and behavioural barriers, which combined are known as 'defence portfolios'.
However, defence strategies of different honey bee species vary, and appear to have adapted in response to the prevalence and severity of threat from local hornet species.
Scientists found that the European honey bee (also known as the Western honey bee, Apis mellifera) that were introduced to Oriental regions, are unable to defend their colonies against attacks by the aggressive Asian giant hornet (or 'Murder hornet'), Vespa mandarinia.
A number of honey bee species make high pitched noises to alert other colony members and ward off threats.
Bees may emit an alarm pheromone to warn nestmates of impending threat of hornets, and stimulate various defensive reactions, which may include some of the behaviours described below.
Forming a barrier, defensive wave
Bees may form a barrier of many bees at the nest entrance, in an effort to prevent entry by hornets. Interestingly, the honey bee Apis cerana has been observed to use animal poop as a deterrent to Asian giant hornet attacks.
Overheating and suffocating
A number of honey bee species kill individual hornets by ‘balling’ the hornets. In doing so, the hornet is killed by overheating, and possibly also by asphyxiation and multiple stings, and perhaps a combination of these.
Defensive bee balling is particularly pronounced in the Asian honey bees, Apis cerana which have to contend with the deadly Asian giant hornet (Murder hornets) Vespa mandarinia or the Giant hornet, Vespa soror.
The video below is about 5 minutes long, and worth watching. The honey bees native to Japan (Apis cerana) have evolved the 'heat-balling' method to perfection. European honey bees (or 'Western honey bee' - Apis mellifera) transported to Japan, are not so effective in their defenses against this dangerous predator.
Below is a table summarizing several research investigations, describing defence portfolios of different honey bee species against attacking hornets.
|Honey Bee Species||Hornet Species||Method Of Defence||Research|
|Apis nuluensis||Vespa multimaculata||Guard bees balled and killed individual hornets with heat.||Koeniger et al 1996|
|Formed heat balls around individual hornets. There were significantly more worker bees in Apis cerana heat balls, with higher temperature achieved than for those of Apis mellifera.||Ken et al 2005|
|Form packed aggregations of bees near hive opening, which may deter hornet from entering. Bees cling together in groups, knock down approaching hornets then balled them, resulting in overheating and asphyxia.||Barrachi et al 2010|
|Apis cerana||Vespa mandarinia|
(Asian giant hornet, or 'Murder hornet')
|Produce vibratory signals and release alarm pheromone to communicate threat at the nest entrance, and stimulate nestmates to prepare to “heat ball” scouting hornets.|
Smearing of plant-based materials around nest entrances, possibly interfering with pheromones deposited by hornet scouts.
|McClenaghan et al|
Fujiwara et al 2016
|Apis cerana||Vespa soror|
|Use animal poop to deter hornets from nest|
entrance. Heat balling of individual hornets.
|Mattila et al 2020|
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