Last week we visited a large spotted orbweaver that had taken up residence beneath the eaves of my front porch. I anticipated this fine predator would soon begin collecting an assortment of interesting prey. This week I was not disappointed to see that in addition to a moth or two, the large spider snared and dispatched two brown marmorated stink bugs. For those of us who dwell in the many parts of the United States, the brown marmorated stink bug has become an inimitable pest attacking apples, vandalizing vegetables, sullying soybeans, and raiding residences. Since its discovery near Allentown, PA, in the middle 1990’s, it has caused millions of dollars of damage to a wide variety of crops and delivered untold distress to millions of homeowners in some 43 states by invading homes from the Atlantic to the Pacific.
Mischief caused by this exotic invader from Asia has been the topic of several previous episodes of Bug of the Week. For those of you who have had enough of this rascal, take solace in the knowledge that several indigenous predators know how to give stink bugs the ultimate comeuppance. Click on this link to enjoy the curious reunion between the Chinese praying mantis and the brown marmorated stink bug. And this link will show you how the wheel bug poked more than just some fun at the stink bug. This week let’s see how another giant web builder, the delightful and stink-bug-lethal black and yellow garden spider, Argiope aurantia, serves up some hospitality for the visitor from Asia.
Wicked fangs help release liquefied stink bug protein to be slurped-up by the spider.
Many of us have shared the experience of wandering along a path through a meadow and bumbling into an enormous spider web ruled by a fearsome yellow and black spider. Argiope aurantia, the so-called black and yellow garden spider, is extraordinarily common this year in some locations. Fortunately for Bug of the Week, one of our eagle-eyed administrators recently captured an impressive female garden spider. This gorgeous creature, whose name coincidently is Charlotte, has taken up residence in a large display case in our building. Garden spiders belong to family known as Araneidae, the orb weavers, made famous by E. B. White in his classic tale, Charlotte’s Web. Webs of the black and yellow garden spider can be gargantuan, often spanning several feet. You may recall that Charlotte used her web to write eloquent praises for her friend Wilbur the pig in an attempt to rescue him from becoming a porcine feast for the farmer.
To my disappointment, our Charlotte only mastered the letter “W”, which she copies repeatedly to create a conspicuously large band of zigzagging “W’s” in the center of her web. Spider aficionados call this band of heavy silk the stabilimentum. The function of the stabilimentum is a topic of debate among arachnologists. Some suggest that the band helps disguise the spider from its predators by providing a form of camouflage as the spider rests in the center of its web. Others believe that the silk may act as a tiny parasol shielding the spider from intense rays of the sun. One fascinating study revealed that the conspicuous bands of silk acted as a visual warning to low flying birds, reducing the likelihood of devastating web-destroying crashes much the same way an image of an owl on a large plate glass window dissuades misguided birds from crashing and breaking their necks. Of course, the spider cares not for the welfare of the bird, but repairing bird-damaged webs takes time away from important projects like capturing and eating insects.
Although I tried to resist poking Charlotte, my curiosity got the better of me and my digital inquiry provoked a remarkable behavioral display. The garden spider retreated slightly from the stabilimentum and began to rhythmically flex and extend its legs. These gyrations set the entire web rocking back and forth. Swaying the web in rhythmic motion is called web-flexing and it is often observed in orb weavers. Web-flexing has been reported as a way to dislodge potential predators or to cause prey to become entangled in sticky capture-threads in the web. Flexing may serve other defensive purposes as well. Enemies of the orb weaver include predatory lizards, toads, and other spiders that rely on keen eyesight to locate and capture prey. In an interesting treatise on orb weavers, Wayne Tolbert suggested that web-flexing might be a clever way for the spider to conceal its exact location, thereby confounding hungry predators.
Rock on spider, rock on.
As fate would have it, swarms of brown marmorated stink bugs inhabit our laboratories and provide a ready source of food for Charlotte. Stink bugs stand no chance once they encounter the sticky strands of Charlotte’s web. The speed with which she immobilizes her victim in a silken wrapper is strongly reminiscent of Frodo’s wicked encounter with Shelob en route to Mount Doom. Sometimes the prey is treated to a bite or two from Charlotte’s impressive fangs. On other occasions, she simply wraps up the stink bug and later fetches it to the center of the web where victims are usually devoured. After a week or so of strict stink bug diet, a very pregnant Charlotte deposited a ping pong ball-sized egg case in an upper corner of her lair. Let’s hope that Charlotte’s feral kin are showing similar homegrown hospitality to stink bugs wherever they may be. They, along with many other home-grown predators, are part of the reason stink bugs are not the problem they used to be here in Maryland.
Once a stink bug blunders into a black and yellow garden spider’s web, it’s safe to say “that’s a wrap.”
Bug of the Week thanks our own arachnophilic administrator Gene for donating Charlotte and providing the inspiration for this episode. Two great articles “Predator avoidance behaviors and web defense structures in the orb weavers Argiope aurantia and Argiope trifasciata” by W. Tolbert, and “Do stabilimenta in orb webs attract prey or defend spiders?” by T.A. Blackledge and J.W. Wenzel were consulted for this episode of Bug of the Week. To learn more about these awesome predators, please visit the following websites:
To learn more about BMSB biology, distribution, and management, please visit the following website: http://www.stopbmsb.org/