spiders

Spiders are invertebrates (they have no internal skeletons) that are members of the Class Arachnida.  Features that define them are that they have eight legs (insects have six), no antennae or wings (insects do), and two body parts - a cephalothorax (cephalo- means head; thorax refers to the mid-section; this contains the brain, stomach, and the venom glands) and an abdomen (contains the heart, lungs, silk glands, respiratory tubes, and the digestive and reproductive tracts) (insects have a head, thorax, and abdomen).

Almost all spiders have eight eyes on the front of the cephalothorax.  The pattern of how they are arranged is important in determining what family each belongs to.  Their eye sight is poor, and they depend mostly on the sense of touch.  When a light is shined on the ground or water at night, each tiny blue shiny dot that is seen is probably a spider.  They are incredibly abundant in our local area. 

Of the many spider families, only two have no venom.  These are uncommonly encountered and very small in size, so the general rule of thumb is that “spiders are venomous.”  the question is, “How venomous?”  As far as we are positive, only two species of spiders in Louisiana are dangerous: the Black Widow and the Brown Recluse.  Neither normally result in death.  The bite of a Black Widow causes muscles to contract and not relax (tetany); the bite of the Brown Recluse results in an oozing sore that takes a very long time to heal.  Even the large tarantulas from central Louisiana and points west are capable of giving a painful, yet harmless (like a bee sting) bite.  The venom of most species is specific to other invertebrates and kills insects and the like very quickly.

The jaws of a spider are called chelicerae, and they may be tipped with fangs.  In the venomous forms, the spiders inject the venom through the fangs to kill the prey then to digest it before the spider chews it and drinks the dissolved prey.  The fangs of most spiders are too short to penetrate the skin of humans.

Another important feature of spiders is the spinneret system.  At the rear of the abdomen are six spinnerets.  Each of these are connected to a gland that produces a specific type of silk.  The spider mixes and matches the various types of silk to produce specific silks for specific purposes.  They do this instinctively and very rapidly.

Since baby spiders are so small, how do they travel great distances and show up in places where they did not occur before?  They use what is called “ballooning.”  The tiny spider climbs to the top of something (a post, blade of grass, whatever), sticks its abdomen up in the air, and begins to spew out a stream of silk.  When enough silk is floating on the breeze to lift the spiderling off its perch, it floats away.  At times the air can be full of ballooning spiderlings, and it is astounding just how much balloon silk can appear in the area over a short period of time.