Tuesday, June 22, 2010

Assassin Bug Larva

I came across this critter crawling on a friends shirt.  It looks innocent at first glance until you notice the distinctive upward turned abdomen and the curved beak tucked up between its front legs.  This is a larval (nymph) of an assassin bug (Reduviidae), a large family with 7,000 species in the family, most of which will go through 5 larval stages before adulthood.  This looks like a wheel bug nymph, a common bug around our cabin.
Assassin bug larva- Patrick Coin
Reduviidae go through an incomplete metamorphosis in which the first nymph (instar) that emerges from the egg has a resemblance to the eventual adult it will become.  The first instar of the wheel bug has a bright red back (picture from Bugguide) which is quite distinctive while the latter instar (pictured above) shows graying much like we humans.  The final stage of adulthood bring them their wings and sex organs.  This is similar to withholding the driving permit and hormones from a teenager.
The adult wheel bug (Arilus cristatus) is easily identified by the gear-like armor on its back.  Like all true bugs, the mouth parts (mandible, maxilla and labium or lips) have evolved into a piercing beak, called a rostrum. It carries it tucked up below its thorax until swinging it out to stab into an unfortunate prey.  Other true bugs, (Hemiptera for you Latin speakers), such as cicadas, aphids, planthoppers, leafhoppers, and shield or stink bugs use their beak of plants.
On the other hand, Assassin bugs are predatory, feeding off the insides of other bugs.  They have strong front legs which tightly grasp their prey as they stab their beak into it and inject digestive juices.  After these have done their work they are able to suck out their dinner like a high protein milkshake.  Most other insects which use this external digestion process have two tubes, one to inject and one to suck out the contents.  Reduviidae have just one large tube to inject and then slurp up the feast.
Wheel bugs tend to move in a jerky motion, and their brief flights produce a loud buzzing sound.  They may bite humans who handle them, an extremely painful experience producing an open sore that can take months to heal.  If that isn't enough to dissuade you from picking one up, their "bad gas" problem may be.  They have two orange glands beside the anus that eject a foul scent when they are disturbed.
To start using "Reduviidae" in conversations with friends, go to howjsay.com.

Good news from the field!  Cynthia Andre reports that her peach tree has lots of Japanese beetles (no surprise there) and lots of wheel bugs including one which she watched stalking one of the beetles.  This serves to remind us that wheel bugs are considered beneficial.

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