Sunday, August 19, 2012

Spider Nursery

Side view of egg case- Click to enlarge
"I get by with a little help from my friends" *
                  -   Lennon / McCartney

Barb found this spider trapped in a waste basket in our well house.  The timing was perfect as we took the arachnid to Insectorama that night and before returning it to our well house maternity ward.  I, like everyone else, identified it as a "wolf spider."  Wrong!

By looking carefully you can see the egg case that she is carrying.  A wolf spider spins a silken pad to deliver the eggs onto, then wraps them up in several layers of silk and attaches them to her spinnerets.  She will haul the case around with her until the young emerge.  This is a unique characteristic of female wolf spiders. 

Dr. Chris Barnhart pointed out my error, a role usually assumed by Barb.  He noted that she is carrying the egg case in her jaws and pedipalps, not her spinnerets.  On looking at the picture above, you can see that her spinnerets at the tip of her abdomen do not contact the egg case.  This is an identifying characteristic of a nursery web spider.

Egg case is off the floor
Her dedication to her young is incredible.  First, holding the egg sac with her jaws precludes eating.  Her only defense against predators is escape or dropping the egg case.  In moving her about and recapturing her during one escape attempt, she held tenaciously to her maternal burden.

Second, carrying the egg sac below is an awkward arrangement at best.  She essentially walks on tiptoes (if a spider can be said to have toes) as she lifts the sac higher so the egg case doesn't drag.   This must be even worse than shopping in Walmart the week of your due date.

Nursery web - Wikimedia
Another key difference in the species is the nursery phase.  A wolf spider's young crawl out of the egg sac and up on to her back where they ride around for a while as she hunts.  They depart at their own pace, apparently ignored by the mother.

Nursery web spiders get their name from the next phase of motherhood.  She weaves a rather haphazard web and attaches the egg sac to it.  The spiderlings emerge and stay within the confines of the web while the mother guards the web.  After their second molt, the young disperse.**

Don't mess with Mama- Note the eyes
While I was photographing her at close range she charged the camera lens several times, trying to get out the little aquarium door.  This gave me a chance for a good closeup picture.  Wolf spiders have four small eyes in a row on the bottom, two large secondary eyes in the middle and two smaller ones on top.  This picture shows two rows, each with four equal sized eyes.  If I had seen her hostile stare I probably would have dropped the camera and stepped back.

Male nursery web spiders take a risk when approaching with mating in mind, as the larger female will frequently look at him as the main course.  To counter this, the males frequently approach cautiously with a "gift" such as a dead fly or some other food offering.  They are even known to bring an insect leg or some other inedible fragment to keep her busy.  That seems like the equivalent of coming in late and bringing your a bouquet of dandelions, but apparently it works some times.

Looking for nighttime entertainment with a real reality show?  Try finding spiders including wolf and nursery web varieties in the dark by their eyeshine, a tiny bright silver spot in the beam of a flashlight.  This is light reflecting off their tapetum, the reflective surface at the back of their eyes.  This same structure is what gives the eyeshine you see from deer and raccoons along the highway at night.

As you can see in this short clip from the clip from Youtube below, the spider doesn't have to be facing you.  The eyeshine is more obvious in real life than in the video.  It is important to hold the flashlight close to your face so the light reflects straight back to your eyes.  An LED headlamp is a good tool for this.

Our spider will soon be back patrolling the well house where there is a ready supply of baby food as well as lots of house crickets to entertain her kids with.

 We discussed other wolf spider habits in the past on this blog.
* That would be Chris Barnhart

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