Friday, April 17, 2009
Green Stink Bug
What better creature to punctuate the week when we file our taxes than a stink bug! Furthermore, the Green Stink Bug is a true bug in the entomological sense. Its mouth parts are adapted into a syringe-like beak which contains a pair of modified mandibles for cutting, and a dual-channel tube through which it can spit saliva to liquify food making it possible to be slurped up through the other channel. In short, it cuts and it sucks.
Name: The Green Stink Bug is Acrosternum hilare. It is a member of the Pentatomidae family which has around 200 species in North America. The penta- part of the family name means five and -tomidae is from the Greek tomos meaning a section. This refers to the five segments in the antennae. Most other terrestrial bugs have antennae with fewer segments. Pentatomidae family members are also known as shield-shaped stink bugs. About two thirds of the species feed on plants. Some are serious crop and garden pests. The remaining third are predators. An example of one of these is the Predacious Stink Bug, Stiretrus anchorago, from the Biodiversity Corner, June 28, 2008. Stink bugs have earned their name because of the strong-smelling fluid they can discharge as a deterrent to predators and an alert for their fellows.
When and where found: On April 9, a friend and I were walking our dogs in the Towle Land when my friend spotted this Green Stink Bug walking across the brown leaf litter on the path. Its color was so vivid it could be spotted as easily as an error in your tax return by an IRS auditor. I pounced on it as eagerly and examined it as closely. Green Stink Bugs overwinter as adults and so it is possible to see them on a warm day in spring.
Distinguishing characteristics: The bug is green, just over half an inch long, and has the characteristic shield shape of stink bugs. When I picked it up I didn’t know exactly what it was or that it would turn out to be so descriptively named. There is a similar bug, the Southern Green Stink Bug, which has reddish bands on the antennae where this one has black bands.
Department of Defense: Adult stink bugs have a single centrally-located stink gland with an opening on each side of the body. They are able to fire the fluid separately from the left or right side as the threat warrants. The smelly (and I presume foul-tasting) discharge deters many predators but not all. Thomas Eisner, in his book For Love of Insects, tells of his experiments with stink bugs and spiders. Using two different species of orb-weaver spiders, he introduced stink bugs into their webs. One species had figured it out. It took pains to wrap the bug in silk so very gently as not to trigger the distasteful discharge. Only then did the spider move in to bite and kill the bug. At this point the discharge could not hit its target and was ineffective. The other spider species was less patient. It was often fired upon by the bug and had to retreat and clean itself before returning to try again. In the meantime the bug used its digestive saliva to convert the elastic threads of the spider web into something brittle which it could break out of.
A convoluted web: Eisner noticed that other insects arrived on the scene to share the spider’s catch. Several species of flies detected the presence of the trapped stink bug and joined in the feast with no fear of being trapped themselves. By this time the spider had moved its prey to the non-sticky hub, the dining room, of its web. By taking a component of the stink fluid (trans-2-hexenal) and applying it to non-stinky prey, Eisner showed that the flies picked up the scent and came in to investigate the likelihood of some food.
Sources: For Love of Insects, Thomas Eisner; Insects: Their Natural History and Diversity, Stephen A. Marshall.
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