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In late summer, many people notice an influx of swarming yellowjackets as their colonies reach peak. Some online reports suggest a surge in the number of wasps this year may be due to the dry and hot temperatures earlier in the summer. 

But are there more wasps in º£½ÇÉçÇø¹ÙÍøright now? Here’s what experts say. 

Is there a surge of wasps in º£½ÇÉçÇø¹ÙÍøright now? 

While there’s no recorded data to indicate an increase in wasp populations this year compared to last, it’s not unusual for people to encounter them more, as the wasps are spending more time outside of their nests to find food. 

Collecting data on the number of wasps in º£½ÇÉçÇø¹ÙÍøwould be very difficult as it’s site dependent, said Chris Darling, a curator emeritus of entomology at the Royal Ontario Museum, explaining that some areas are more suitable for wasps depending on if there’s flowering plants or nesting sites available. 

In Toronto, there are several types of wasps with different nesting requirements such as the ground, trees or places with shelter such as near homes. 

“Depending on the nature of the area, people are going to potentially have more or less of these insects,” Darling said.

Wasps’ peak season is typically in mid-July and it lasts until autumn when we get hard frost and they, except for the queen, start to die off. 

It may just be your perception that there’s more wasps and this is just part of the regular cycle, according to Doug Currie, an entomologist and senior curator of insects at the Royal Ontario Museum.

Do hotter temperatures affect wasp populations? 

Yellowjackets tend to thrive in hot and dry temperatures, so it’s a “logical prediction” that a hotter summer could provide conditions for a surge in wasps, Darling said, but stressed that this hasn’t been backed up by any data. 

“Their activity patterns, their reproduction, and their entire lives are to some degree mediated by the temperature. So if you have really cold weather, their development is slower than very hot weather,” he said.

Weather will determine how large the colony will get, how many they’re going to generate and how many worker wasps are going to be outside in search of food for the development of the colony. 

The number of wasps may be linked to changes in the urban environment determining how hot it may be, such as the number of concrete highrises and deforestation. 

Wasps are daytime creatures that tend to hunker down in cooler, cloudy conditions. They prefer sunshine, but hot and dry weather may also knock down some wasp numbers, Darling said, as wasps do need rainwater to survive. 

Prolonged heat events may also cause stress among some insects, including those that are prey to wasps such as caterpillars, which could reduce a major protein source.

Why are wasps aggressive during the late summer?

Wasps may appear more aggressive amid a decline of their natural food supply as summer comes to an end. 

Wasps are active starting in the spring but humans only tend to notice them as summer ends because they interact with us looking for sugar from our food such as pop drinks. 

It’s why you may see more yellowjackets attracted to outdoor dining. 

Earlier in the summer, foraging wasps spend more time hunting for protein to feed the young in the nest, using their stingers to capture caterpillars, chew them up and then spit it to feed the nest’s larvae.

“After the adult workers feed the larvae in the nest, the larvae in return will exude a nutritious solution that feeds the adult because the workers are incapable of eating solid food,” Currie said.

In later summer, the larvae then pupate and no longer require protein to grow which means the foraging wasps will not receive the “sweet” fluid from the larvae which Currie said is when “we run into trouble with them.”

” If they’re hauling away pieces of your hamburger, that means their nests are still active and they’re trying to feed their young. But if they’re mainly after your soft drinks or other sugary type substances, that means that their nest is finished and they’re out just fending for themselves,” he said.

Is climate change related to aggression in wasps? 

Hot summer temperatures would have to be “really extreme” to notice an effect on wasp aggression, said Currie, and insects have adapted to temperatures over millions of years. 

“Their behaviour patterns are determined genetically, and it’s going to take a long time to change, so they’re not going to get more aggressive. They’re going to be as aggressive as they always were,” Darling said.

What types of wasps are typically seen this time of year in the GTA ?

There are quite a few different species of wasps in the GTA, but almost all of them come down to one to two species that make themselves quite prevalent: the vespula germanica (German wasp) and the vespula vulgaris (yellowjacket).

These wasps are both capable of stinging which can cause a painful inflamed welt, and for a few, a severe allergic reaction. 

Forager female wasps have stinging agents, most male wasps don’t, however the queen wasp isn’t capable of stinging. 

“They use their stingers, or actually what the queen would use to lay eggs, but they’re modified into stingers in the workers because they don’t produce young themselves,” Currie said, adding that they use their stingers in their search for prey and in self-defence against predators.