Monday, July 13, 2015

Eastern Harvestman

"Oh look, those spiders are fighting," one of our young visitors said.  This didn't seem like a time to talk about birds and bees so I limited my response to an explanation of the difference between Harvestmen (Opiliones) and spiders, discussed in a previous blog.

I thought the harvestman in question was likely the Eastern Harvestman, Leiobunum vittatum, which is a favorite "lab rat" for researchers in the Opilione field.  I was surprised when it was identified as a male Leiobunum crassipalpe, the first time it has been reported to Bugguide.

Males and females communicate by sexually specific chemical clues.  Then the fun begins.  The dance begins with the male trying to get the female in his embrace.  The success depends on the size of the males pedipalps according to research published in Behavior.  The answer to the age-old question, "Does size matter?" is "Yes" and in Opiliones, the answer is smaller is better!  Shorter pedipalps have more mechanical advantage and thus give the male a better grip on a potential mate.  On the other hand, larger male size relative to the female will determine how fast mating occurs.

This species is extremely common around Bull Creek.  Some sources say they are nocturnal and secretive but I had one ride on my ATV for 2 hours in 90 degree heat.  I walked around the outside of our creek house just now to photograph a mating pair.   I counted 14 clinging on the walls, although none were mating at the time.  Ken Sproule's photograph below captures the romance of first contact much better anyway.

 Mating dance, not a fight -
According to an old myth, you could find lost cattle by picking up a harvestman and holding all its legs but one.  The free leg would supposedly point in the direction of the lost cow.  I would caution you to avoid this as the legs are very fragile, breaking off and twitching like the tail of a skink to distract its predator.  Another myth said that if you killed a harvestman it would rain the next day.  "Would which ever one of you has been killing all of them please stop, we have had enough rain for a while!"

Determining the exact species from a photograph is difficult.  There are over 130 Leiobunum species and identification depends upon details like sexual organs, mouth parts, etc.  The specimen below was posted with the comment "...stocky palps like L. crassipalpe, but the abdomen is long and pointy, like L. vittatum."  Experts frequently debate these points, leading to naming and renaming debates.  Fortunately for the perpetuation of the species the Leiobunum are able to determine who is who.
Palps grasping, mandibles at work.  Marshal Hedin CC
 These photographs were the first reported to Bugguide.