Bleeding Spider

 

I received this gift of a spider to identify.  There had been two of them, possibly mating only this one couldn't get away.  It was in a jar and was having trouble getting around with a noticeable "limp," dragging its two front legs.  We couldn't decide if it was trauma related or possibly a male victim of a female's post-mating snacking.

Big eyes on top, four below

Click to enlarge

The first step in spider identification is to look into their eyes.  Getting one to sit still for a facial photograph can be a chore but this one wasn't moving well so I got a full frontal view.  The arrangement of eyes can be diagnostic of the spider's family using tables such as the one on Spiders.us.  The slightly concave arrangement of the 4 lower eyes suggested Zoropsid family but they don't occur in the Midwest so I was left with the possibility of a saggy Wolf Spider whose eye pattern is usually more convex.

Of more interest to me was the clear fluid which was on the table.  Close up I could see blebs on a leg and just behind the chelicera on the right side of the cephalothorax.  My friend didn't think it was injured during the capture so this likely was from the other spider.  I suspect that these were drops of spider hemolymph, i.e. spider blood.  This gets a bit complicated so stick with me (or move on to cat videos on Youtube).

Spider's blood is different from  mammal's blood.* In humans and other mammals the oxygen is bound to hemoglobin, a molecule that contains iron and gives the red color to blood cells. In spiders and some other arthropods, such as crustaceans as well as most mollusks, the oxygen is bound to a different molecule called hemocyanin that contains copper instead of iron.  The hemocyanins are proteins in the lymph rather than in blood cells, colorless in the reduced or deoxygenated state while oxidized copper gives a blue/green color to the oxygenated blood. Therefore spiders have clear to pale "blue" blood.

Spider's respiration is far different from insects.  This from the American Tarantula Society explains it far better than I can:

"The exchange of O2 and CO2 in insects is accomplished by an often complex system of air tubes, made up of trachea and the smaller tracheoles. The air tubes suffuse through the body in close contact with insect tissues. Hemolymph components are not needed to assist in gaseous exchange between the tissues and the air tubes. This point is driven home when you consider what happens with some insects, such as certain grasshopper species. When on the move, the blood is apparently being circulated around the body sufficiently, because the heart stops beating. The swishing around of the blood caused by movement is enough for the hemolymph to fulfill its function, which is largely distribution of nutrients, water, and the movement of wastes to the malpighian tubules for removal (roughly the insect equivalent of kidneys). The heart begins beating again when the insect stops moving."

Most spiders and insects are so small that any blood produced by squishing them is never noticed.  The exception is from an insect that is sucking your blood.  The take away is if it is red after you swat it, it was your blood!

Spider blood  http://askascientist.nz/z158
Spider respiration  http://atshq.org/articles/Respiration.pdf
*  Findaspider.org
=====
A recent article caught my attention by mentioning that most of us have fewer bugs splatting on our windshield than we did 20 years ago.  For those kids reading this, a 30 mile car trip in the "old days" left the windshield covered with spattered insect bodies.  Is something more serious going on?  Read this on Where have all the insects gone?