November 27, 2013
Wanted Dead or Alive (No, Just Dead)
By ANNE RAVER
This Thanksgiving, I’ll be thanking the bugs, not the turkeys, for sustaining me in the wilderness. In my case, the wilderness was of the stink-bug variety.
It all started about a month ago, when a friend called to tell me about a big spider with a bright black-and-yellow pattern on her back.
“I was leaning over the tomato plants and I almost stuck my head in her web,” said Anne Todd, 49, a massage therapist in Parkton, Md. “My first thought was, ‘Oh, my gosh, it’s ugly.’ But the more I watched her, the more beautiful she became, and the more things I saw about her. Her coloring is incredible, and she has all these neat stripes on her legs.”
The spider reminded both of us of the title character in “Charlotte’s Web.” It also made me think of the mythical golden orb weaver, which spins a web of gold silk, although Ms. Todd’s Charlotte was busy catching her prey in a three-foot web with a zigzag pattern in the middle, strung between the house and a tomato cage.
A call to a few entomologists quickly identified her as Argiope aurantia, a common garden spider in the Northeast.
But Michael J. Raupp, an entomologist at the University of Maryland, mentioned something else that caught my attention. “Spiders are vastly important predators both in home and agricultural landscapes,” he said. “And they’re lessening the impact of the brown marmorated stink bug.”
This Asian bug, which was first spotted in the 1990s in Allentown, Pa., and is now in some 40 states, has caused millions of dollars in damage to crops. Scientists initially thought it had no natural predators here, so I was thrilled to hear that this wasn’t the case — particularly since it has been sucking the life out of my Brandywines for four years. Any spider that kills this stink bug is a friend of mine.
Dr. Raupp had posted a couple of videos of Argiope aurantia capturing and devouring a stink bug on his Bug of the Week blog. I clicked on Oct. 7 in the archives and watched a stink bug struggling to free its legs from the sticky silk of a web, as A. aurantia swooped in and wrapped it up, pulling silk from her abdomen with lightning speed. The second video showed her injecting the stink bug with digestive enzymes and slurping up the liquid protein. Hurray!
“Stink bugs are higher in protein and lower in fat than a steak,” Dr. Raupp told me when I called his office.
But a lot less appetizing. I had to ask: Had he ever tasted one?
“I have,” he said. “The worst bug I ever tasted. I spat it out in five seconds and my tongue went numb.” Dr. Raupp, it should be explained, spends a lot of his time in the field, chasing bugs — and eating them, too. He likes the way they taste, and he thinks they could be a solution to world hunger. “Cicadas are mighty good eating,” he said. “So are termites, grasshoppers, crickets and mealworms. Bugs make up an important part of the diet in many cultures around the world. One way around the protein shortage is to consume insects rather than cows.”
Then he gave me something else to be thankful for: Argiope aurantia isn’t the only arthropod going after these stinky pests. Some praying mantises and wheel bugs have also been feasting on stink bugs, and therefore proliferating.
“We have people reporting dramatic increases in mantises and wheel bugs, and our own observations tell us this is the case,” Dr. Raupp said. “A decade ago, if I saw a half-dozen wheel bugs in autumn, I would feel blessed.” This year, he said, “I’ve seen half a dozen wheel bugs on the trunk of a single tree eating stink bugs.”
I realized I had been seeing more mantises in my garden as well, but it had never occurred to me to wonder why. I also remembered seeing a wheel bug crawling up the side of the barn door recently.
The wheel bug (Arilus cristatus) looks like a creature out of “Star Wars,” with its two long antennas, powerful orange beak and the spoked wheel on its back. It is worshiped by organic gardeners because it feeds on a variety of insects and its presence indicates a healthy ecosystem free of pesticides.
“They’re the lion or the eagle of your food web,” Dr. Raupp said. “They sit on top. When you have these big, ferocious predators in your landscape, that tells me that this is a very healthy landscape, because all these other levels in your food web are intact.”
Three species of praying mantises are stink-bug slayers: the Carolina mantis (Stagmomantis carolina), the European mantis (Mantis religiosa) and the Chinese mantis (Tenodera sinensis). I never knew there was more than one kind of praying mantis, but I was beginning to think that the stink bug may be the road to enlightenment.
The Chinese mantis is the largest, about four inches long. “It’s usually green, with brown legs and brown wings,” Dr. Raupp said.
The native Carolina mantis is two to two and a half inches long, with a body that is mottled gray-white or tan.
The European mantis is two to three inches long, and it has a little black bull’s-eye with a white center on the inside of its foreleg. But as Dr. Raupp said, “If you ask her to show you her armpit, she might grab you with those raptorial legs and give you a taste of her spines.” You won’t die, however (unless you’re a stink bug).
It’s great fun watching these insects eat the enemy.
Tracy Leskey was positively gleeful. Dr. Leskey is the project director for a research team funded by the Department of Agriculture to study the brown marmorated stink bug, in an effort to control its rampage across the country. “I saw a praying mantis on my house eat the legs of a stink bug first, so it couldn’t run away,” she said. “Then it chewed on it, like a sandwich.”
The Department of Agriculture has poured $5.7 million into the research of this team of more than 50 scientists. The project’s website, Stop Brown Marmorated Stink Bug, is packed with information and updates on exactly who is feasting on the foe (not to mention juicy videos of stink bugs meeting their fates).
Dr. Leskey is exhilarated about the work of wheel bugs, too. “We’ve seen the wheel-bug nymphs and adults just chasing down stink bugs on catalpa trees,” she said.
And now parasitic wasps, no bigger than tiny ants, are stepping up to the plate.
The female wasp inserts its eggs into the stink bug eggs, which cluster like little pearls on a leaf or the bark of a tree, said Paula Shrewsbury, an entomologist on the research team. “The wasp eggs hatch, and the larvae then feed on the good stuff inside, developing until they chew their way out and emerge as adult wasps,” she said. These parasitic wasps reduced the number of stink bug eggs by 40 percent in one study site.
But as Dr. Raupp reminded me, this is simply nature taking its course. Last summer, when a farmer called to say there were thousands of praying mantises in his cornfield, he told the man it was just a numerical response. “There is more food out there, so the mantids can make more babies and the babies don’t starve,” Dr. Raupp said. “We started to see an uptick in some of these predator populations three or four years ago. It’s the classic predator-and-prey model, like the lynx and the hare.” (He was referring to the lynx of the Northwest Territories, which can starve without the snowshoe hare.)
Closer to home, it’s like the aphids sucking the life out of your roses — until the hoverflies and lady beetles eat them up. But few survive if gardeners and farmers nuke the planet with pesticides. That’s why the Department of Agriculture is funding research to try to find biological controls for this particular pest, which has been so devastating to the country’s crops.
A parasitic wasp from Asia, studied in a quarantined laboratory in Newark, Del., may also be released, pending approval, in the next year or so, said Kim Hoelmer, a research entomologist who brought the species back from Asia. “In Asia, these wasps will parasitize up to 80 percent of the stink bug eggs,” he said. “We appreciate what natural predators are doing, but they’re not doing it well enough, if we want to rely on biological controls.”
Late last month, as the days were growing colder, my friend Ms. Todd watched Charlotte lay her fourth and last egg case, on the far corner of her web. “I noticed that her colors weren’t as bright,” she said. “She seemed sort of withered. I went out one morning and she was dead, her color all gone, hanging by her feet in the middle of the web.”
Ms. Todd was filled with sadness. “I had lost my garden friend,” she said. “She had made her last egg sac the day before. It must have taken everything.”
Ms. Todd had watched Argiope aurantia grow round with eggs three times before, over the course of the summer, each time laying them in a ball and wrapping them with silk.
“But I’ve never seen a male spider,” she said. We wondered where he was, and how he fertilized the eggs.
I called a few entomologists, who told me that the male Argiope aurantia is a fraction of the female’s size and has a heart attack as soon as he deposits his sperm inside the female. She eats him sooner or later, sometimes wrapping him up and stashing him in her web like an energy bar.
How little we gardeners know of the dramas unfolding in our universe.
The four spider egg sacs in Ms. Todd’s garden are tightly wrapped with silk and look tough enough to survive the winter. By midspring, the babies should emerge. After a few days, they will balloon off on a gentle breeze to spin their first little webs, low in the grass. By midsummer, the females should be spinning big webs, three feet wide, with that same zigzag pattern in the middle, its purpose debated by scientists.
I vowed to look for them next year. For now, the garden sleeps.
A walk through the yard or woodland may reveal clusters of barrel-shaped wheel bug eggs, a hundred or so laid within a circle about the size of a quarter, on the smooth bark of a sycamore tree. Or the egg sac (ootheca is the scientific term) of a Carolina mantis. Dr. Raupp, a bug lover if there ever was one, said, “It reminds me of a nice loaf of bread, half an inch long.”
As for Ms. Todd, she is keeping an eye on Charlotte’s oothecae.
“My golden lady of the garden has passed on,” she said. “But I look forward to watching her babies.”
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