Friday, November 4, 2016

Wireworms


The WOLF Students found these insect larvae while studying a rotting log.  These are large wireworms, the larvae of a click beetle.  They are a dramatic example of complete metamorphosis where the larva bears no resemblance to the adult.  They have the typical mouth parts and six legs but lack the shape and the wings of an adult.  Our wireworms spend a lot of time backing up which demonstrates the rigid way it holds its body in this video.

Head and thorax - dorsal view
Wireworm is a generic name for the larvae of all species of click beetles in the family Elateridae.  They have tough bodies like a crawdad, the abdomen hinged in 10 segments.  These were 45 cm long with a color pattern common to many species such as the Large Wireworms - Orthostethus infuscatus, but I will leave further identification to the experts.  Most wireworms are saprophagous, living on dead organisms, but some are predator of insect larvae.  Some species are agricultural pests of corn and other crops and they get most of the studies.

The most popular of the click beetles is the Eyed Elater, Alaus oculatus.  It is larger than most click beetles, almost two inches long and its distinctive appearance separates it from any
other beetle. The prominent false eyes on the beetle are presumed to be a defense against predators although no proof of this exists.  Its wireworm larvae are predators of larvae of wood boring beetles and flies.  They have two anal hooks which our specimens lack.  These wireworms and some other species spend 2-5 years as larvae in soil and rotting wood.

Click beetles are named for their ability to flex their body forward and snap a spine on the prosternum into a groove in the mesosternum, producing a violent "click" that can bounce the beetle into the air.  The description of this mechanism is still somewhat confusing to me but the beetle has it down pat.  When the beetle is on its back it is unable to right its self with its legs.  The "click" sends it up to 8" in the air but its landing on its feet is a random event out of its control so it may require several tries.  This also may be an effective way to escape predators.

If you run into an Eyed Elater, test its click out.  Holding the abdomen will frequently get it to click repeatedly.  Putting it on its back should get it to jump as in this video.  If annoyed enough it may fly away but it is slow, awkward and seldom goes very far.  Then let it go to do its good work, producing more wireworms.

Most comprehensive source of the Eyed Elater is at this site.


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