Why Wasps and Hornets Get More Aggressive in Fall
Seemingly out of nowhere, yellow jackets come at you and strike at blazing speed. Their venom hurts like the devil. How do you deter yellow jackets and eliminate wasp nests? Learn all about how to avoid yellow jackets as well as prevent and treat yellow jacket stings.
In late summer and fall, untamed places abound with gorgeous displays of late goldenrod, joy-pye, and fall asters, but some less-welcome visitors are the yellow jackets and other aggressive wasps.
Unlike honeybees, bumblebees, and gentle native bees, yellow jackets are extremely aggressive insects at this time of year. Yellow jackets are predatory social wasps which can be distinguished from bees by their thin "waists." Bees have thicker waists and their bodies are fuzzy.
A yellow jacket stings multiple times without dying and injects venom into its victim. (A honeybee can only sting once.) Both honeybees and bumblebees will only sting defensively, while yellow jackets are easily provoked. They attack in swarms and will give chase over long distances if they feel threatened.
Please note: We're not saying that wasps do not have an important part of the ecosystem! In fact, they are excellent at regulating populations of insect pests. They are parasites of caterpillars, aphids, whiteflies, and a lot of other insects which eat crops, and save farmers money. They are also pollinators for a lot of native plants, such a goldenrod, and many fruit trees such as figs.
However, yellow jackets tend to be quite aggressive around this time of year as natural sugar sources decline and they need to find energy. They are scavengers of meat and sweet liquids, which brings them in frequent contact with humans (whereas honeybees are visiting flowers for nectar and keep away from humans). Let's briefly understand the yellow jacket's life cycle:
The Yellow Jacket's Life Cycle
- In spring, yellow jackets start building nests of extraordinarily sophisticated architecture—underground, suspended from tree branches, under the eaves, in shed rafters, in wall cavities, and sometimes in abandoned cars. Within the nest, the wasp queen lays eggs which will mature into adult workers.
- All summer long, the yellow jacket workers capture and kill caterpillars and other soft-bodied insects which, along with carrion, serve as protein foods to feed their growing broods. They sip flower nectar, rotting and damaged fruits, and tree sap to supply the energy to feed themselves.
- In late summer, the queen begins laying the eggs that will develop into potential queens and a few males (called drones) which will mate with the queens.
- As fall progresses and supplies of prey insects and overripe fruit decline, the wasps become increasingly aggressive in defending their expanding nests. You'll see wasps showing up at barbecues and picnics and hovering near trash cans. They are going after both the meats (to feed their larvae) and the sweets (candy, desserts, sugary drinks) to furnish themselves with energy.
- In late fall, the workers, the drones, and the queen herself will all leave the nest and die. Only the mated queens survive, burrowing into leaf litter and hibernating in suspended animation until spring.
How to Prevent Yellow Jacket Stings
From late summer on:
- Keep garbage cans and recycling bins tightly closed and far away from children, playgrounds, and social areas.
- Don’t wear perfume or other scented body products when you’re out and about performing yard and garden work. The wasps may mistake a floral scent for actual nectar-producing flowers.
- Stay aware. Watch the ground around you to look for wasps entering and leaving holes in the ground that lead to their underground nests. Approach outbuildings slowly and cautiously, looking up under the eaves and rafters; wasps will buzz out and around the nest hole to warn you not to approach further. Give them a wide berth and they are unlikely to attack.
- If you have the task of mowing tall grass or whacking weeds, wear protective clothing, including boots (long pants tucked inside), long sleeves tucked inside gloves, and face protection. (I use a bee veil.) Wasps nesting underground will sense the vibrations from power equipment and may strike from some distance away.
How To Avoid Yellow Jacket Stings
Resist the urge to swat, slap, and run away. The wasps may perceive rapid movement as even more threatening.
Move away slowly, covering your face with your arms, and keep moving.
If you’ve disturbed the whole colony and many wasps have come for you, run into a densely shaded spot; wasps prefer bright sunlight.
Don’t jump in a pond if one is nearby. The wasps will hover around waiting for you to surface, then immediately attack your head.
How to Treat Yellow Jacket Stings
Most people develop pain, redness, and swelling around the site of a wasp sting.
Self-care involves spreading a paste of baking soda or table salt and water over the area immediately after the sting, then later applying an ice pack to reduce the swelling.
However, some people have a severe, potentially life-threatening, reaction to a yellow-jacket sting, or stings. Get medical attention immediately if:
- You’ve received many stings.
- You’ve been stung in the mouth or throat.
- You begin wheezing or sweating profusely.
- You have difficulty breathing or speaking.
- If your throat or chest feels tight.
- You break out in hives.
- You feel nauseous, dizzy, or severely anxious.
Talk to your doctor about carrying emergency medication to use in case this happens again.
Eliminating Wasp Nests
Yellow jacket nests are built out of paper fibers and are most often under ground, but they can also be seen under eaves. They are covered with a single opening, unlike paper wasp nests, which have exposed, honey-comb–like nests.
Because all wasps are useful to us as insect predators, experts suggest leaving their nests alone unless they pose an imminent threat to human or animal health. Mark the area, and stay away from it until the wasps all leave in late fall. They won’t return to the nest next year.
But when yellow jackets have stung or built their nest near the home or outbuildings, or in the path of human activities, you may want to eliminate it.
Here’s what to do:
- If it’s a very large nest or if you’ve ever had a severe reaction to wasp or other insect stings, hire a licensed exterminator to handle the job.
- If you decide to do it yourself, identify that the stinging insect is indeed a yellow jacket or other aggressive wasp. Mark the location of the nest without getting too close.
- Buy a pressurized can of wasp and hornet jet spray that sprays a solid stream of insecticide spray that will reach 10 feet or more
Then follow UNH Cooperative Extension entomologist Alan Eaton’s excellent instructions:
- Treat at night when yellow jacket are least active and most workers will be in the nest. Use a flashlight with a red filter over the bulb. Wasps can’t see red light well.
- At least two hours after dark, quietly and carefully approach the colony and thoroughly spray into the entrance. Don’t give a quick shot; spray for several seconds to make sure the spray penetrates deep into the nest.
- After spraying, walk away immediately and stay away for a full day. For ground colonies, carry a shovelful of soil with you to cover the entrance before you walk away.
- Coveralls can be helpful, especially if they are slick, smooth material worn over other thick clothing. Many people choose Tyvek.
- If wearing a shirt and pants, securely tape or tuck them together at the waist.
- Wear boots. Wasps may crawl over shoes and sting your ankles.
- Seal the pant cuffs securely over the boots with tape or rubber bands.
- Protect hands with leather or heavy rubber gloves, securely sealing the arms to the gloves at the cuffs.
- A beekeeper’s hat and veil will keep wasps away from your face and neck. Make sure to fasten it to the clothing around your neck and shoulders.
If you get stung, here is how to treat bee and wasp stings.