Monday, August 20, 2012

Itsy Bitsy (Cobweb) Spiders - Thank goodness for good tools!

For many years I have been intrigued with the very small spiders that live around the porch light and back door frame at my home in Irving, TX.  Now that I have the SEM Lab at Eastfield, I can finally get a good look at them and classify them.

In fact, I may have taken too good of a look and have dozens of images to post to this blog.  For this first installment I will post the images taken with my point and shoot camera and those taken with the dissecting scope in the SEM Lab.

Lots of cobwebs covered in prey insects. These spiders love the overhangs from the sections of aluminum siding.

Red arrow indicates the spider in its web which is full of prey.

I got this little spider out of hiding by touching it. 
It fell downward on an escape thread and then held very still.
Scale above spider shows 1mm gradations.

Egg sac spun by adult spider.

Top corner of door frame.  The red arrow indicates the spider - blue arrows indicate egg sacs.
(I can also see that I need to do some caulking.)

While in the collecting vial overnight, the spider spun a cobweb. 
This image shows the sticky droplets that help capture prey.

Well hello there!  A first portrait.
The spider has been preserved in 70% propanol with a little glycerol added

This is a ventral view (the under side of the spider).
You can see the two body sections, the cephalothorax or prosoma, and the abdomen or opisthosoma.
Also clearly visible are the 4 pairs of legs and an anterior pair of pedipalps.
Notice also that the spinnerets are not at the end of the abdomen, but are underneath the spider. This was very helpful in identifying the spider as belonging to family Theridiidae.

Pedipalps with claws visible.  You can also see the chelicera and fangs.

Side view showing downward facing spinnerets and narrow pedicel that connects the prosoma and opisthosoma.

Eye arrangement is important in identifying spiders.  This first look threw me off the trail since it looks like the spider only has 6 eyes.  It turns out, and it is obvious under the SEM, that the outer most eyes are paired - a dyad.
There are two rows of eyes, the anterior eye row and the posterior eye row.  In addition there are anterior median eyes (AME), anterior lateral eyes (ALE), posterior median eyes (PME), and posterior lateral eyes (PLE).  On this spider the the ALE and PLE form the dyad.

Spiders exchange gases via a highly folded book lung. 
I got lucky with the light and was able to photograph the book lung as indicated by the black arrow.

Spiders spin an egg sac to contain their eggs while they develop. 
I collected two egg sacs to image.  Notice the little spiderling outside of the egg sac (red arrow).

I didn't want this posting to be too long so it contains no scanning electron micrographs. I will post those images tomorrow, so please check back.

If you are interested in doing spider work let me recommend some books.
  • How to Know the Spiders by B.J. Kaston, 0697048993  This is the classic from 1978 and I would suggest beginning with this book since it is inexpensive.  Updates to the book are available online.
  • The Biology of Spiders by Rainer Foelix, 3rd Ed., 0199734828  Not an identification guide, but will tell you so everything you want to know about spiders.
  • Spiders of North America: An Identification Manual by Cushing and Ubick, 0977143902  This guide is Kaston on steriods.  Pricey, but well worth it for identifying spiders.
Eastfield College is dedicated to supporting STEM research at all levels.  If you would like to become involved with the Scanning Electron Microscopes at Eastfield please contact me.

Murry Gans
Scanning Electron Microscope Lab Coordinator
Eastfield College
Mesquite, TX

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