Monday, November 1, 2010

Sticks in Love

Click to enlarge
Stick insects seem to come out in great numbers in the fall.  There are 33 species in the US, compared with 2,000 species worldwide.   They belong to the order Matodea, and our most common species is the Northern Walking Stick (Dipheromera femorata).  This species eats the foliage of deciduous trees, mainly oaks.

Their defense is in their resemblance to dry sticks with green legs looking like leaf petioles.  They even have the ability to rock back and forth like branches blowing in the wind.  When approached, they may freeze in a defensive maneuver like deer and rabbits frequently do to avoid detection.  In addition to looking more stick-like, holding still offers other protection as most predators will avoid eating dead prey.  Amazingly, if this fails and something tears its leg off, it can escape and then regenerate a new leg, a very unusual trait among its fellow insects.

Stick insects grow from the eggs laid in leaf litter in the fall.  They grow by molting, the youngest being simply smaller versions of the sexually mature adults.  It is common to find mating pairs such as the ones above, with the male tightly clasping the back of the female.  The reason we find them mating so often is that the male will hang on for days.  This is thought to be a behavior not driven by the male’s excessive lust so much as to prevent other males from fertilizing his female and displacing his gene pool.*

Another trait is the population explosions seen in some years.  In 2008, we saw this occur with stick insects all over our Bull Creek house and trees.  Who knows?  Maybe it was lust after all.

* This behavior and other strategies are discussed further in Olivia Judson's book, Dr. Tatiana’s Sex Advice to All Creation, p. 9.
For more than you ever wanted to know about walking sticks, look at Phasmatodea.com

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