Yellowjackets play a supportive role in gardening but can be dangerous around families and pets. People sensitive to bee venom should be especially careful from August through October, when yellowjacket numbers peak.

They attack when threatened, and are known to crash cookouts too.

“Yellowjackets, hornets and paper wasps are all beneficial predators of soft-bodied insects such as caterpillars, grubs and flies,” said Heather Stoven, a horticulturist with Oregon State University Extension Service. “However, yellowjackets will often begin to scavenge late in the summer into fall as their typical food sources often become more limited.

“They begin to look for carrion (think your hamburger at a picnic) as well as sugary foods … which can lead to increased negative encounters,” Stoven said.

Yellowjackets deliver the insects and food they forage to the young in their nests, while nourishing themselves on nectar from flowers.

That makes them inadvertent pollinators, although they aren’t as efficient as honeybees since their shiny bodies have little body hair where pollen can collect for transfer from plant to plant, Stoven said.

Yellowjackets typically live in underground burrows, although some species build paper nests elsewhere.

“Their nests are usually small and placed under protective overhangs on houses and garages,” said James Dill, a pest management specialist with University of Maine Extension. “Where you run into a problem is when you’re mowing the lawn and come across a ground nest. You don’t usually see those until it’s too late. Disturb those nests and they react terribly.”

Yellowjackets are drawn to food and water, the latter particularly during droughts.

“Yards contain all kinds of potential food sources such as fallen fruits, which provide sugars, garbage, pet food and human food,” Stoven said.

It’s best to remove nests found in high-traffic areas, but do so carefully, she said. Probably the smartest option is calling in an exterminator.

If you do want to take on the job yourself, then use quick-acting, kill-on-contact insecticides labeled for yellowjackets that allow treatment from safe distances when aimed at nest entrances, Stoven said. Apply the insecticide when it’s cool, and avoid using a flashlight, since wasps are attracted to light.

“Wear protective clothing that covers your skin,” Stoven said. “If a nest is in a location that can be avoided, it could potentially be left undisturbed. The queen and workers will die off when cold weather arrives.”

Traps, commercial or homemade, are another kind of management tool, although they’re effective only in small areas and don’t impact the nests where queens produce colonies sized anywhere from 1,000 to 5,000 wasps, said Susan Jones, a professor of entomology at The Ohio State University.

“Certain yellowjackets have been known to fly from 300 to 1,000 yards from their nest in search of food,” Jones said. “Traps will not rapidly knock down yellowjacket populations. For effective use at outdoor events, traps should be placed out two or more days prior to the event.”

Firewood piles also are frequent gathering places for yellowjackets, since they continue collecting nest material through summer, Dill said.

“They like split wood, not the bark,” he said. “Keep the piles covered, which also keeps the wood nice and dry.”

Plant lovers have long gotten together to trade seeds and growing advice, and the latest generation is following suit with modern plant swaps.

The swaps (sometimes called plant exchanges) for amateur horticulturalists are popping up in homes, parking lots, trendy gardening stores and online. They’re about exchanging advice and meeting like-minded people, says 35-year-old Ana Carlson, who has attended several plant swaps in New York City and Los Angeles, where she lives.

“People just talk and it is fun,” she said. “I don’t go looking for plants because I have more than enough.”

Carlson, who owns an online “plant decor” shop, Sill Appeal , and has nearly 200 houseplants, initially learned about the swaps through social media a few years ago, when plants became a hobby.

“They’re very social events,” she said. “Every time I go, I meet people.”

While plant swaps can include outdoor varieties, many people trade houseplants, which are back in style thanks in part to social media. Instagram has been flooded with “Plantstagrammers” or “plant influencers,” who post daily photos of houseplants under a variety of hashtags, including #plantcommunity (559,000 posts) and #houseplantlove (118,000 posts). On Pinterest, plant devotees display a plethora of photos, blog posts and articles chronicling unusual, colorful and pet-friendly houseplants.

“Right now, the plant world is kind of insane,” says Sue Eggen, the creative director at Urban Jungle , a plant shop in Philadelphia. “It’s like the 1970s all over again — the coolest thing millennials can do is care for plants.”

Last month, Eggen and the Urban Jungle team organized a plant swap for some 50 customers who purchased tickets. There were snacks and beverages, and attendees listened to a live recording of Bloom and Grow radio , a podcast from Broadway actress Maria Failla that’s all about houseplants.

Some plant lovers come to swaps for expensive and rare finds. A full-size pink princess philodendron or a variegated monstera, two fashionable plants not readily found in gardening stores, can cost upward of $150 retail. At a plant swap, however, someone might bring in a cutting that can be propagated.

“People blew me away with what they brought in,” Eggen said.

Bala Rathinasabapathi, a professor in the horticultural sciences department at University of Florida, says the produce found in grocery stores today is a result of ancient plant swaps.

Humans domesticated plants about 10,000 years ago, and plant exchanges followed shortly after,” Rathinasabapathi said. “People used plants like currency.”

Today, however, swaps are mostly characteristic of urban areas, he said.

Philadelphia resident Christina Tessaro, 37, learned of a local plant exchange group on Facebook with more than 7,000 members. She originally joined the group to learn more about plants after she took a job at the Philadelphia Horticultural Society. Soon, houseplants became a hobby.

A couple members of the group have organized plant pop-up nights throughout Philadelphia for people to meet in person and socialize.

“I got to meet a few people I recognized online,” Tessaro said. “It’s been really nice to put a face to a name.”

Online swaps have also expanded social circles for long-time plant lovers.

“We started out swapping plants as teens,” said Stan Miklis, 62, of Dallas, who studied horticulture in high school in Texas. He said he attended plant parties as a teen and young man.

Now, as a farmer, he learns of new plant swaps via the Internet.

“My whole life is and has always been plants,” Miklis said. “All my friends are from the plant circle.”