Asian hornets. A threat to solitary bees or bumblebees?

Are honeybees, bumblebees and solitary bees safe from the Asian Hornet?

The Asian Hornet, Vespa velutina, or yellow legged hornet, is the first invasive predator of honeybees and has now arrived in the UK. It is known to have caused serious problems for European honeybees Apis mellifera. Hives provide a large food resource, concentrated in a small area. As such Monceau et al states that because it predates upon honeybees, it disrupts their ecological role, potentially alters diversity, harms commercial beekeeping activities and is potentially deadly to allergic people, (although according to  the National Bee unit, it poses no greater risk to human health than a bee). Will the Asian hornets cause problems for our solitary and bumblebees as well?

Different defence strategies

How do honeybees defend themselves from hornets? This article describes the different honeybee defence strategies used by the European and also the Asian honeybee, Apis cerana. when encountering hornets. As you read on you will find researchers have found the Asian honeybee deals with hornets, including the Giant Asian hornet, more effectively than the Europeans. Thankfully it has NOT arrived here!

Hornet species

In Europe we have two native hornet species, the European Hornet Vespa crabro and the Oriental hornet, Vespa orientalis, which is mainly found in the sub-Mediterranean regions. In its native range, the Asian Hornet is common throughout central to eastern Asia, where natural predation and competition control its numbers. Although slightly smaller than our own, V. crabro, the size of their colonies, (at least three times larger than V. crabro), will cause alarm.

How did it arrive?

According to Roberts, it was first recorded in France, 2005 and is thought to have arrived in a container of pottery from China before 2004 via Bordeaux. It spread rapidly throughout neighbouring areas, invading honeybee hives there and then moving onto Spain, 2010, Belgium 2011, Portugal 2012, Italy 2013, Channel Isles 2016 and now reaching Tetbury, Gloucestershire, England Sept. 2016.

Nests and nesting sites

Nests are foundered by a single queen who was fertilised the previous year. From early spring to late June, foundress queens can be found flying. This long winter emergence period may be a strategy used by the non native hornets as a ‘bet-hedging’ strategy, i.e. spreading the risks with them being new to an area or if they find themselves in an uncertain environment. After emergence from her hibernation site, she starts to build her papery, wasp-like nest and lays eggs, quickly increasing the size and numbers throughout the summer.

According to Roberts, nests are rarely found in holes in walls or in the ground. They nest in garages, sheds, under decking, shrubs, roofs, eaves, in or on tall trees in urban and rural areas. It appears they avoid conifer stands! More neighbour disputes possible then…. “I’m keeping them to stop the hornets!”

Food resources.

She and her workers will forage on carbohydrates provided by flower nectar, tree sap or depending upon the season, ripening fruits. Males may be seen nectaring on ivy during autumn.

For the brood they require protein in the form of other insects, honeybees, social wasps and spiders. Although being opportunists, carrion, stalls of waste from butchers or fishmongers is also on the menu.

Weakens already weak hives

From what I can gather, the Asian hornet, picks off individual honeybees as they return to the hive or are out foraging. They may not risk attacking a healthy strong hive when alone. However, a weak hive is a different matter and after weakening the hive even further by picking off individuals, they may attack the already weakened hive en masse.

Native UK wild bees

I have only ever found 2 hornets nests here, thankfully both accidentally! I have never seen any predating upon a bumblebee nest or a solitary bee hotel. Whether having large numbers of solitary bees using bee hotels is likely to attract the attention of V. velutina, I am not sure. I think its possible. At the moment they pick of individual honeybees as they return to the hive. If they found a solitary bee hotel with returning solitary bees this may prove an easy target and very tempting for them.

I have seen photos and films of the European hornet killing honeybees. Likewise whether or not the huge numbers of mason or leafcutter bees, as used in N. America for pollination, has attracted predation by the European hornet, now established in many states there, I have not heard.

Honeybee hive attacks

Both the Asian honeybee, Apis. cerana and our European honey bee, A. mellifera employ fundermentally different strategies when threatened by hornets, who, as is usual in predator-prey relationships, use their own attack methods and strategies to overcome the defences.

Wasp-Hawking Video by the Animal and Plant Health Agency

Wasp-Hawking

Researchers in China, found that Asian hornets, when dealing with honeybees near their hives, have specialised in hawking honeybee foragers returning to their hives, (wasp-hawking). This involves the hornet taking a position in front of the hive entrance with its back facing the hive allowing it to face and observe returning foragers. They hover 30-40 cms from the hive entrance and pluck individual honeybees from the air as they return after foraging, presumably because they weigh heavier and are therefore slower.  Arca et al describes how, after intercepting the honeybee, they carry the prey to a nearby shrub, cling to a branch and make a flesh pellet by cutting off each leg, throwing the abdomen to the ground and masticating the thorax, which it carries off to the nest. I have seen our wasps do exactly the same with bluebottles.

Flight strategies

They described that both hunter and prey would use stealth flying, bees would use evasive flying methods, hornets would display wheeling and jinking flight.

Hive Defence strategies

Outside the hive

Tan Ken et al observed that A. mellifera, instead of using a fast approach direct to the hive entrance, slowed down and sashays upon seeing the hornets. Perhaps it recognises the threat and almost freezes expecting the inevitable, or hesitates as it thinks of its next course of action? But by increasing its exposure time and slowing down, this behaviour increases the chance of predation and thereby more losses of honeybees occur.

Inside the hive

Bee Carpet

Both species were found to deploy the so called ‘bee carpet’ at the hive entrance. A. cerana deploy threefold more guard bees to ward off predation than do A. mellifera. When under hornet or wasp attack, A. cerana reduced foraging time and remained in the hive. A. mellifera, did not reduce foraging time, thereby reducing numbers available to engulf a hornet and extends the exposure time of being predated whilst out or returning from foraging.  Over time the sustained and increasing predation of the A. mellifera by the hornets from summer to autumn, weakens their colony and may lead to increasing colony death during winter. A. cerana, have a more efficient and aggressive defence of the hive than A. mellifera.

Visible and audible alarm communication

Tan Ken et al  states that A. cerana will signal to each other by a collectively executed and timed shimmering of their wings causing a waved effect only when the hornet directly approaches the hive, a visible alarm communication that helps them resist predation and rally the troops. A. mellifera does n’t do this.

Heat-balling

After the given signal, the bees are alerted to the next stage of their strategic defence, heat-balling. The signal, alerts more bees and by using more bees in a heat ball when under attack and by performing a heat ball more often, when under attack, increases the success of heat-balling the hornet.

Practice makes perfect

Whilst both species may kill the hornet by heat-balling, A. cerana heats up faster and to a higher core temperature than the core temperature of balling A. mellifera. It would appear that the A. cerana perform this more effectively, more efficiently and more often than A. mellifera. They concluded that strategies deployed by A. cerana are be more effective than those used by A. mellifera.. Let’s hope they learn fast!

Not just a load of hot air!

However, recent research by Arca et al of the thermo-balling of a giant Asian hornet  V. mandarinia, by A. cerana, found it was a combination of heat, a high concentration of CO2 and relatively high humidity that all interacted together to kill the hornet.

Interestingly, the native Italian honeybee, A.m. ligustica, has learnt to heat ball our own native hornet, V. crabro, by ‘cooking’ it and probably asphyxia, Co2 or humidity may all play a part.

From all of this ‘balling behavioural strategies’, it would appear that the success depends upon successfully forming a ball to fully engulf the hornet so as it cannot escape and the desired combinations as described above, proves lethal.

Known predators of European Hornets

Jays, European bee-eater and badgers are predators here in Europe.

Known Predators of Asian Hornets in France

Roberts states that in France, during the pre winter decline of the colony, green woodpeckers, jays and tits were seen pillaging nests and remaining larvae. I doubt very much such predators would have done so prior to the winter decline! Recently  in France, a honey buzzard was seen attacking and destroying an Asian hornets nest as were chickens, although at what time of the year is not stated.

Conopids to the rescue?

The parasitoid Conops vesiclaris has been shown to parasitise queen Asian hornets in France by French researchers. I have watched Conopid flies as they literally fly towards and slam into flying bumblebee workers and even target them when they have landed on flowers to forage. Job done, egg laid into their host abdomen.

National Geographic film

This film show Asian honeybees dealing with what looks like a Giant Asian Hornet. They deal with other hornets entering the hive in a similar fashion. If only they could teach our native honeybees how to do it properly!

Research needed.

How far will these hornets forage from their nests?

Can a sexual pheromone and therefore a suitable trap be developed?

What hibernation sites do they prefer?

What distance is a nearby water resource when siting a nest? This may indicate where to concentrate searches for nest sites.

How far north can they survive?

Badminton anyone!

Looks like a badminton racket may be useful as this account describes it’s use along with other control methods to defend honeybee hives.

Other useful downloads:

For probably the most detailed and comprehensive information todate, download PDF  Vespa velutina: a new invasive predator of honeybees in Europe

Download the Asian Hornet NNSS Species description PDF 

Report sightings of it here

A Simple monitoring trap for Asian Hornets (Nat. Bee Unit)

For more information about None Native Species