Why Does A Stinkbug Stink?

“Look, dad!” my son shouts, voice excited as he points. “A stinkbug!”

We’re walking up the front stairs to our condo. I glance in the direction he’s pointing, and see nothing.  “Cool,” I tell him.

“Why do stinkbugs stink?” he asks.

I unlock the front door. “I don’t know,” I answer. “I think maybe they spray stinky chemicals.”

What is a stinkbug?

Getting information on stinkbugs in general proved to be a little difficult, as Google just keeps giving me hits for the Brown Marmorated Stink Bug (Halyomorpha halys), an insect native to China and Japan that is an invasive species in North America.  Wikipedia, when you do a search for ‘stink bugs’, takes you to a page about family Pentatomidae, a family of insects belonging to order Hemiptera.  Shield bugs and stink bugs belong to Hemiptera, with stink bugs comprising Pentatomidae.

I couldn’t find a list of the species native to North America.  Heck, I couldn’t even find a list of the species of Pentatomidae, end of statement.  But, here’s a brown stink bug that is native to this continent:

native_brown_1242026

That particular bug is Euschistus servus, and it is a common pest throughout southern Canada and the northern United States.  This particular bug is about half an inch long (10 to 15 mm), and lays a bright yellow egg mass (around 60 eggs) that turns pinkish as they get ready to hatch (between four and five weeks after being laid).  Larval stink bugs require about 29 days to reach maturity.  Adults are able to fly, and are primarily omnivores.

Brown stink bugs often feed on the vegetative parts, flowers, stems and foliage of the plant, as well as the seed, nut or fruit, and this makes them important pests of many crops.

Brown stink bugs are found on a variety of hosts, such as shrubs, vines, many broadleaf weeds, especially legumes, as well as cultivated crops such as corn, soybean, sorghum, okra, millet, snap beans, peas and cotton.

Do stinkbugs stink?

Yes, they do.  Here’s what Orkin has to say on the subject:

Their name comes from their smelly defense mechanism. Stink bugs have the ability to emit a strong deterring odor, from their body glands, whenever they feel threatened or injured — much like how a skunk defends itself. The smell varies depending on the species and the person’s olfactory senses, but it has often been compared to strong herbs and spices like cilantro and coriander.

Interesting enough, the composition of the odor is comprised of chemicals commonly used as food additives and is present in cilantro. This smell can linger for hours so, if possible, try to avoid stink bugs or carefully sweep or vacuum them up if they have entered your house, unless you want a face full of intense-smelling herbs and spices.

A more detailed description of the specific chemicals used by one particular species of stink bug may be found in Chemical Defense in the Stink Bug Cosmopepla bimaculata, an article published in the Journal of Chemical Ecology back in 1999 and freely available on the internet.  From the abstract,

Adult Cosmopepla bimaculata discharge a volatile secretion from paired ventral metathoracic glands (MIG) when disturbed. Collected volatiles were similar in both sexes and consisted of n-tridecane (67%), (E)-2-decenal (12%), (E)-2-decenyl acetate (12%), (E)-2-hexenal (3%), hexyl acetate (2%), n-dodecane (2%), a tridecene isomer (l%), and n-undecane, n-tetradecane, and n-pentadecane (all <1%). In addition. undisturbed males produced a novel insect compound. (E)-8-heneicosene. whose function is unknown.

No, I don’t know what any of those are.  But every resource I found agrees on a few things about stink bug spray:

  1. It smells vaguely of spices and cucumber
  2. Despite that, it does not smell good.
  3. No, really, it stinks like old garbage.

So, to answer the original question, why do stink bugs stink?  Because they don’t want to get eaten.  Again, as the abstract of Chemical Defense in the Stink Bug Cosmopepla bimaculata put it, “In feeding trials, killdeer (Charadrius vociferus), starlings (Sturnus vulgaris), robins (Turdus migratorius), and anole lizards (Anolis ccarolinensis) rejected or demonstrated aversion to feeding on the bugs. Furthermore. bugs that lacked the secretion were more susceptible to predation than bugs with secretion, suggesting that the secretion functions in defense against predators.”

 

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