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Diet, demographics behind late-summer wasp outbreak on Prairies

鈥業t was dangerous, we couldn鈥檛 go into some parts of our yard鈥
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A wasp hovers over a tulip on a warm spring day in Washington Park on Thursday, May 2, 2013, in Albany, N.Y. An outbreak of wasps has forced an Edmonton school to hold a recess period indoors and restaurant servers around the city to warn patrons of guests in yellow jackets. THE CANADIAN PRESS/AP, Mike Groll

Audric Moses has seen a few late-summer wasp outbreaks around his Edmonton home over the past seven years, but nothing like what he saw last week.

鈥淢y wife said, 鈥楬ey, come on out here. You need to see this,鈥欌 he said.

鈥淭here were apples in the tree that were completely covered in wasps, inside and outside of the apples. They were just eating their way into the centre, leaving a hollow skin of an apple behind.

鈥淭he population of wasps just seems to have exploded in the last week.鈥

Late summer is often wasp time on the Prairies, as the little stingers go through their natural cycle. But this season seems a bit more yellow-and-black than normal.

鈥淚鈥檝e been hearing a lot from southern and central Alberta that it seems like it鈥檚 big wasp season,鈥 said University of Alberta entomologist Maya Evenden.

It鈥檚 the same to the east, said her colleague Sarah Wood at the University of Saskatchewan.

鈥淚 do hear from people who are getting stung in their backyards,鈥 she said. 鈥淧opulations may be higher this year than average.鈥

Many would agree.

On Friday, kindergarten to Grade 9 students at Edmonton鈥檚 Shauna May Seneca School were kept indoors for recess because there were too many wasps in the schoolyard. Restaurant servers in the city have also been warning prospective patio-sitters that they may have fellow diners in yellow jackets.

The City of Edmonton says its pest management team has removed 374 wasp nests so far this year and is in the process of removing more. Last year, it got rid of 121.

While there may be a bit more buzz to this summer鈥檚 wasp season, there鈥檚 nothing new about the reasons for it. Wasp demographics and food supplies create the same effect every year.

Firstly, said Evenden, wasp colonies have had all summer to nurture their eggs and bring larvae to adulthood. By now, there鈥檚 a whole new generation of grown-up wasps thirsty for a sip of the wine in your glass.

鈥淭hey鈥檝e had that season to build up their colony size,鈥 Evenden said. 鈥淭here鈥檚 more of them from each colony.鈥

Evenden added that unusually hot weather across the Prairies in July may have quickened the growth of the larvae and helped more of them survive.

As well, late summer is when wasp diets shift. Earlier in the summer, wasps are able to feed their young without too much trouble 鈥 a balanced diet of flower pollen and the larvae and young of other insects.

But by this point in the season, those prey insects have all grown up and flowers aren鈥檛 quite as abundant.

鈥淭here鈥檚 less nectar available in the environment,鈥 said Wood.

鈥淭hey need to look for other resources. That鈥檚 why they鈥檙e after human food as well as honeybees鈥 food. There鈥檚 just less to go around.鈥

That relative scarcity has another effect that does not go unnoticed.

鈥淭hey seem a little bit more aggressive,鈥 said Evenden.

Evenden said people should look more kindly on wasps. They鈥檙e important plant pollinators and play significant ecosystem roles, even in suburban backyards.

鈥淧eople give them a bad rap,鈥 she said.

But Moses wishes they鈥檇 play that role somewhere else. A wasp trap he set out in his backyard was full of dead bugs in a day.

鈥淎ll of the liquid bait was gone,鈥 he said. 鈥淚t was just wasp bodies.

鈥淚t was dangerous. We couldn鈥檛 go into some parts of our yard.鈥

The outbreak in his yard may be abating, a little. The next wasp trap took two days to fill.

As the fall weather cools, wasps stop laying eggs and slow down. Eventually, all the wasps in the colony die, except for a few fertilized females that hunker down for the winter to wait for spring.

Then they can begin rebuilding the colony and start the whole cycle over again.





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