Monday, July 7, 2014

Male Black Widow Spider's Rhythm

Black widow spider dorsal view - Click to enlarge
A recent story on Nature World News described a set of "good vibrations" produced by the male black widow spider, Latrodectus mactans.   Like many other spider species, the female black widow may eat the smaller male that is coming in to mate if his intentions are not perfectly clear to her. Many spider species have distinctive mating rituals or courtship signals.  Not so the male black widow which relies on rhythm.  When approaching the female, the male shakes her web at a particular frequency, signaling that he is coming to mate and not coming as dinner. 

Unlike the way we were traditionally taught, the female black widow doesn't commonly eat its mate, the basis of its name "widow."  Any insect or other prey, including other spiders, will set off a vibration by their touching the web.  The research, published in Frontiers in Zoology, found that the male black widow consistently produced a distinctive web vibration, creating low-amplitude ‘whispers’ of love.   This gives a whole new meaning to the term "safe sex."

Black widow egg cases - click to enlarge
I was reminded of this research when I got a call from our neighbor Sheila who had found what looked like a black widow but was "too big."  It was guarding two egg cases and it looked too big to me also.  I had to manipulate it for some time before I could see the distinctive ventral abdominal red hourglass.

Black widow egg cases and spiderlings - click to enlarge
I put the egg cases in a small plastic box, sealed to prevent their release in the creek house and an early end to our marriage.  The next day we had a whole box full of spiderlings, suspended in a 3-dimensional array with tiny strands of silk.

Black widow spiderlings - click to enlarge
The hatchlings are light colored and become darker with each molt until they reach the smooth black color of adulthood.  The female's abdomen is globose (round) while the male's is more oval.  Females' abdomens are said to be wrinkled and somewhat deflated after they have laid their eggs and spun the sacs.  A female may have 3 or 4 egg sacs at one time, each containing anywhere from 100 to 900 yellow eggs.  As our spider was still tightly globose and had only two egg sacs, I suspect she wasn't through her cycle yet.  Over a lifespan of 1 to 2 years a single female may produce 9 to 15 egg sacs!  No wonder she can looked shriveled.

More detailed information on L. mactans is at

1 comment:

  1. Fascinating Bob! Very informative ~ as usual!