A sting in the tale

The long, hot sum­mer of 2018 has been fab­u­lous for wasps of all species – es­pe­cially for ded­i­cated hor­net watch­ers.

BBC Wildlife Magazine - - Contents - HELEN ROY is an ecol­o­gist at the Cen­tre for Ecol­ogy and Hy­drol­ogy and an ex­pert on non-na­tive species.

Ex­plore the so­cial world of the hor­net with a pho­tog­ra­pher who gets a buzz out of these striped in­sect preda­tors

Afew years ago I was am­bling through the wood­lands of the RSPB’s Arne re­serve in Dorset in pur­suit of striped la­dy­birds. These are a fairly scarce and lo­calised species as­so­ci­ated with Scots pine, and Arne hap­pens to be great for them. Sud­denly, with­out warn­ing, I came across some much more im­pos­ing in­sects: I found my­self near pa­trolling Euro­pean hor­nets – the largest species of so­cial wasp na­tive to this coun­try, or in­deed the con­ti­nent. A steady stream of these chest­nut-and-gold in­sects flew by me. They were sim­ply mes­meris­ing.

I felt im­mensely priv­i­leged. For while hor­nets may be big and some­what in­tim­i­dat­ing, they are char­ac­ter­is­ti­cally se­cre­tive – far more so than the com­mon wasps with which we are more fa­mil­iar (and which made their pres­ence felt dur­ing 2018’s long heat­wave). Stand­ing just a me­tre or two from the Arne hor­nets, I was cap­ti­vated by their beauty – and, yes, their calm.

Hor­nets are rel­a­tively com­mon in ma­ture woods across cen­tral and south­ern Eng­land, but also oc­cur in parks and ru­ral gar­dens.

They are ex­pand­ing in range, and now can be seen as far north as Northum­ber­land. I en­counter in­di­vid­ual hor­nets rea­son­ably fre­quently in and around my own gar­den in Ox­ford­shire, and am al­ways de­lighted to get a glimpse of these al­lur­ing preda­tors. But one man has taken things a step fur­ther.

Stephen Powles has long had a pas­sion for hor­nets, and quite lit­er­ally has a win­dow into their se­cret lives, thanks to a rather spe­cial nest­box that he has made in the con­verted barn where he lives in Devon, with a win­dow fac­ing into his spare bed­room. He had been hop­ing to at­tract blue or great tits, but ended up host­ing a much more in­ter­est­ing species.

Unexpected vis­i­tors

In­stead of wel­com­ing birds, the nest­boxes have for the last few years been oc­cu­pied by hor­nets – and Stephen is de­lighted. His pas­sion for these wasps is in­spir­ing. “My in­ter­est in hor­nets be­gan when they moved into one of my barn-owl nest­boxes,” he says. This choice of nest site is not that unusual, since hor­nets read­ily use roof spa­ces and out­houses, as well as hol­low trees. What is a lit­tle out of the or­di­nary is that Stephen’s barn-owl nest­box was built into the gables of his roof. Up there, the hor­net nest was able to reach im­pres­sive di­men­sions.

“One sum­mer I climbed into the loft to check for pos­si­ble signs of a roost­ing barn owl,” Stephen re­calls. “I care­fully opened the ‘back door’ of the nest­box, only to be greeted by 200 or 300 irate hor­nets. I don’t know who was more sur­prised – them or me! I quickly closed the door again, and so be­gan a 15-year fas­ci­na­tion with these in­sects.”

Since then, Stephen has spent hours cap­tur­ing hor­net be­hav­iour on film and in pho­to­graphs, cre­at­ing a uniquely de­tailed per­spec­tive on the life his­tory of, in his words, “these much-ma­ligned su­per-wasps”. In 2016, BBC Wildlife writer Mike Dil­ger even paid a visit, with film crew in tow (their re­mark­able film is still avail­able to view on BBC One’s The One Show web­site).

Hor­nets are closely re­lated to a num­ber of other so­cial wasps within a group called Ve­spinae. Many of these are yel­low and black, whereas hor­nets are yel­low and brown. Hor­nets are large wasps, with queens reach­ing about 3.5cm in length and work­ers about 3cm. They are com­monly con­fused with queens of the me­dian wasp, but lack the deep black mark­ings of that species. Ad­di­tion­ally, hor­nets do not have yel­low mark­ings on the tho­rax, while the me­dian wasp has dis­tinc­tive yel­low bands run­ning along its sides and the work­ers are, of course, much smaller than hor­nets.

In re­cent years, the Asian hor­net has also been much in the news in this coun­try, though as ever with non-na­tive species, some of the re­port­ing has been sen­sa­tion­al­ist. Slightly smaller than the Euro­pean hor­net, this species has yel­low ends to its legs, un­like the all-brown legs of its rel­a­tive. Its head is dark from above but or­ange in front, while

“My in­ter­est ac­tu­ally be­gan when hor­nets moved into one of my barn-owl nest­boxes.”

the head of the Euro­pean hor­net is yel­low from above and to the front.

Hor­nets are de­scribed as ‘ad­vanced eu­so­cial wasps’ – that is, they form a colony com­pris­ing over­lap­ping gen­er­a­tions, with the adults rep­re­sented by the re­pro­duc­tive queen and non-re­pro­duc­tive work­ers. The work­ers un­der­take var­i­ous tasks, from car­ing for the lar­vae that de­velop in small cells within the nest, to for­ag­ing for food, wa­ter and nest ma­te­ri­als. There is some ev­i­dence that, as with hon­ey­bees, worker hor­nets take on dif­fer­ent tasks at dif­fer­ent stages in their short lives. “The life of a worker hor­net is cer­tainly very busy,” says Stephen.

Clearly, the queen hor­net has the most im­por­tant role in the colony – that of pro­duc­ing off­spring. In­deed, she is mother to all the in­di­vid­u­als within the colony, which can even­tu­ally, as with the nest in Stephen’s owl box, grow to in­clude sev­eral hun­dred work­ers. Like other so­cial wasps in Britain, hor­nets have an an­nual life-cy­cle – in other words, it be­gins afresh each year, start­ing with the emer­gence of a mated queen from her win­ter hide­out. Stephen has fi­nally suc­ceeded in doc­u­ment­ing most stages of this fas­ci­nat­ing cy­cle, which ends with the demise of the en­tire colony, ex­cept for the newly mated queens.

A mated queen hor­net will spend the win­ter alone in a shel­tered po­si­tion, such as un­der bark or in a crevice of some kind. In com­mon with many Bri­tish in­sects, she is dor­mant through­out the cold win­ter months. In spring, she emerges to find a suit­able nest site – at this time of year, queen hor­nets can be seen for­ag­ing for wood fi­bres, scrap­ing dead wood with their strong mandibles and mac­er­at­ing it with saliva to form a pulp for con­struct­ing a small, em­bry­onic nest re­sem­bling a sphere.

In­side are hexag­o­nal cells that open down­wards within struc­tures known as combs. The queen will lay her first brood of eggs in these cells; these eggs hatch af­ter about a week and the queen rears the lar­vae on a mix­ture of mashed-up in­sects and spi­ders. A preda­tory role is im­por­tant; by feed­ing on in­ver­te­brate species, hor­nets con­trib­ute to the func­tion­ing of our ecosys­tems. It is an in­ten­sive start to the year for the queen hor­net, who feeds on car­bo­hy­drate-rich sub­stances such as nec­tar and hon­ey­dew – or even honey stolen from colonies of bees.

Af­ter about two weeks, the hor­net lar­vae have gone through five growth stages called in­stars and are ready to pu­pate. Each larva pro­duces a silk-like sub­stance to close its cell and then pu­pates for a cou­ple of weeks. The newly emerg­ing adult worker rasps at the sur­face of the silk cover with its strong mandibles, slowly ro­tat­ing its head while pro­gres­sively scrap­ing away, and only cut­ting through the cover once it has been breached.

The new worker hor­nets then re­main in the nest for a few days be­fore tak­ing their first flight. Dur­ing this time they ful­fil the

A preda­tory role is im­por­tant; by feed­ing on in­ver­te­brate species, hor­nets con­trib­ute to a func­tion­ing ecosys­tem.

im­por­tant task of rais­ing the tem­per­a­ture of the cells they sit on. The way in which so­cial in­sects can con­trol the tem­per­a­ture of their nests is quite in­cred­i­ble. Not only can hor­nets warm up cells, but they can also re­duce the tem­per­a­ture by rapidly beat­ing their wings to fan the cells or by de­liv­er­ing and spread­ing cool­ing wa­ter to the sur­face of the cells.

The first brood of adult work­ers takes over the nest-build­ing work and looks af­ter the new broods hatch­ing from the queen’s eggs. So the colony grows. Ev­ery sec­ond counts to en­sure its sur­vival. “Hor­nets will con­tinue to fly well af­ter dark on warm evenings all through the sum­mer and early au­tumn,” Stephen points out. “Like moths, they’re at­tracted to the lights in our homes. So hor­nets can be seen cir­cling out­side se­cu­rity or porch lights, or fly­ing up and down lit win­dows.”

Things don’t al­ways go to plan, how­ever. There are a num­ber of guests – some pos­si­bly un­wel­come – some­times to be found within the hor­net nests. Some are sim­ply scav­eng­ing and feed­ing on left-overs within the nest, but there are some bee­tles and par­a­sitic wasps that will feed on the de­vel­op­ing brood.

Later in the sea­son, the in­ter­nal ar­chi­tec­ture of the nest changes, as large cells are built to ac­com­mo­date the rear­ing of new queens. At this stage males, char­ac­terised by their long, black an­tenna and lack of a sting, will also be pro­duced, but they will usu­ally be as­signed the smaller cells. Be­fore the on­set of win­ter, the found­ing queen is ne­glected by the work­ers and she dies.

An­nual life-cy­cle

Now the young queens and males emerge from the nest and mate. Most queen hor­nets mate with only a sin­gle male. This is not al­ways the case, how­ever: some­times a queen might mate with two or three males, but even in that sce­nario, most of the queen’s off­spring will be eggs fer­tilised by only one of the males, so the fe­male work­ers are still ex­tremely closely re­lated. Fol­low­ing mat­ing, the queens set­tle down for the win­ter and the work­ers all grad­u­ally die off.

The mag­nif­i­cent sight of hor­nets in flight is cause alone to stop and watch, but when you delve a lit­tle deeper, you re­alise these wasps are mas­ter­minds of ar­chi­tec­ture and so­cial or­gan­i­sa­tion. “The ways in which in­di­vid­u­als within a colony work to­gether is in­spir­ing and cap­ti­vat­ing in equal mea­sure,” says Stephen.

If you are for­tu­nate enough to see hor­nets, then please do, like Stephen, take your time to observe them. En­joy the be­hav­iour of these in­cred­i­ble aerial preda­tors, though keep a safe dis­tance and don’t cross their flight paths. While Stephen has spent “count­less happy hours” very close to hor­net nests, this is not with­out its risks. But as his pic­tures on these pages show, these un­sung he­roes of the in­sect world are worth cel­e­brat­ing.

FIND OUT MORE Bees, Wasps and Ants Record­ing So­ci­ety: bwars.com

Above: A queen re­turns to her nest in a grassy tus­sock. The Euro­pean hor­net Vespa crabro feeds on in­sects and other in­ver­te­brates, sup­ple­mented by sug­ary sap from trees and wind­fall fruit.

The queen be­gins build­ing the nest in spring. The lar­vae de­velop in hexag­o­nal cells which are sealed with a cap made from a silk-like sub­stance un­der which they will pu­pate.

Clock­wise from above: a male (note the long black an­ten­nae) basks on a tree stump while look­ing for a queen to mate with. The lar­vae de­velop in hexag­o­nal cells where they are fed by the work­ers. Note the pro­tein ball (prob­a­bly in­sect wing mus­cle) that has been brought to the nest. Lar­vae of the hor­net rove-bee­tle, which of­ten lives in the nest with the hor­nets and feeds on their de­tri­tus. The nest is built up layer by layer.

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