If yellow jackets have become a pest for you, and if history is any indication, you might need to deal with them for a few more weeks. That is because once we get our killing frost, majority of the yellow jacket population will be wiped out. 

John Gavloski is an Entomologist with Manitoba Agriculture. He says now is the time of year when yellow jackets have more interaction with humans, and notes there is a good reason for that. 

“I can’t really say that it's worse than normal. Every year, come about mid to late August, you have this big... it seems like the population explosion, but the reality is, things are building up throughout the year, we just don't notice it as much.” 

According to Gavloski, yellow jackets are social insects. And, because they are social insects, their diet changes throughout the year, thus making them more noticeable later in the summer. 

When it comes to yellow jackets, only the queen survives the winter. That means it is the queen who gets the new nest going in spring. The queen will start laying eggs and then over the course of the summer their nest grows bigger and bigger. 

Early in the season, adult yellow jackets get their sugar from a few sources, including nectar and tree sap. And, because their young ones are sugar dispensing machines, the adults will return to the nest with an insect, give it to the larva who will eat it and secrete a sugary solution which the adult feeds on. 

Gavloski says for most of the season, the adults will get their sugar from the young ones. But, then late in the season, the main dominant queen will stop laying eggs and eventually die, after living about one year. As a result, there is no longer an abundance of larvae back in the nest and the adults need to find their sugar source elsewhere. The social structure of the hive has disintegrated, and the yellow jackets need to start fending for themselves. 

"That's when they end up coming to your garbage cans, your decks, your picnics," he says. "They are looking for anything sugary they can find." 

Gavloski says they are not highly aggressive, just determined. 

"They become very persistent, and again, that's when we usually have interactions with them," he explains. 

According to Gavloski, a yellow jacket's diet will change throughout the year. Early on, when they need to feed the young ones, they look for protein to give them. This can be in the form of caterpillars, flies, other insects or even a chunk of meat. Late in the season, it is sugary items that are most attractive.

close up of a yellow jacket waspThis is the time of year when the yellow jacket wasp population is at its greatest, and they are all looking for sugary substances. (Photo Credit: John Gavloski)

Gavloski says yellow jackets serve as a natural biocontrol early in the season. They remove caterpillars from the garden and will take care of the diamondback moths from your plants. For the record, he notes they do very little pollination. 

If you happen to spot a large nest in an area where a lot of people congregate, Gavloski says it may be wise to get rid of it, though he suggests leaving that task for someone who knows what they are doing. But, if you find a nest in an area where it is of little concern, he says just let it be. If they are ruining your picnic, he recommends covering food that has been laid out. 

Gavloski says yellow jackets have interesting mouth parts. They have a tube for sucking up liquids and mandibles for chewing things like caterpillars. However, they do not bite humans with those parts. Rather a stinger at the back of their body is their weapon. Unlike a honeybee, a yellow jacket can sting repeatedly if it wants. 

"They will have no reason to want to sting you unless you are a direct threat to their nest or you are aggressively trying to keep them away from your food," he says. "Sometimes if people get a bit too aggressive with the swatting, that's when they are more likely to get stung." 

Gavloski says if you can remain calm, the yellow jacket may just go away. Sometimes a few gentle swats will keep them moving. However, if you are near a hive, and the insect feels threatened, it can release a pheromone which tells all its sisters that there is danger, and a more coordinated attack is needed. 

As mentioned, once southern Manitoba receives its first hard frost, yellow jackets are usually wiped out, aside from the queen. He notes the queen will usually find an area underneath some bark in order to make it through the winter. The queen will never return to its original nest in spring, but rather build a new one from scratch. 

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