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Arachnophobia, an abnormal fear of spiders, has possessed me all my life. If I feel a spider crawling on my skin I flinch and brush it away. At the same time I marvel at the beauty and engineering of a spider web. This spring while walking in my neighbor’s hay field I noticed a small spider sitting in the middle of its web. Dew drops on the web reflected the early morning sunlight so I photographed the web with my cellphone; now the image accompanies this article. Curiosity about web making prompted me to read about the physiology of spiders which has now instilled in me respect and awe for this quiet, mostly harmless creature and subsequently lessened my fears. Many children’s books about spiders are available, but for adults, I recommend, “Biology of Spiders” by Rainer F. Froeliz (1996) to understand the complex nature of spiders.
Recent publications now claim that over 40,000 species of spiders live on Earth. All spiders are carnivorous, eating other animals mostly insects. Over 99 percent of spiders possess poison glands to create venom to kill and paralyze prey. The vast majority of spiders have fangs incapable of breaking through human skin so spider bites are rare. Only the brown recluse and black widow spiders of south and central United States are poisonous and dangerous to humans. Spiders capture prey by two methods either snaring in a web or hunting in the case of a spider on eight feet.
A spider I collected on my front porch is 0.5 centimeters or one-quarter inch long with legs each 2.5 centimeters long. Inside the tiny spider body are packed vital organs to build webs, chase prey, mate, breathe, pump blood and escape from predators. Spiders are characterized by two major body sections, the head containing eyes, jaws, fangs, rudimentary brain, and poison glands and the abdomen containing the lungs, heart, reproductive organs, excretory system, silk glands and spinning apparatus or spinnerets.
All spiders produce silk but some only to protect sperm and eggs. The two sections are connected by a thin waist. The poison glands generate venom which the spider expels into the prey after biting through its covering. Prey juices are sucked into the spider stomach. Nerves extend from the primitive brain to eyes, legs and hairs on the feet which sense vibration and motion. Thin skinny legs contain striated muscle fibers just like in larger animals allowing spiders to run rapidly for short distances. Special paired grasping hands called “pedipalps” near the mouth hold prey and the female during copulation. Silk glands produce up to six different silk threads each serving a specific function. Silk glands direct silk protein to paired spinnerets consisting of up to 1,000 spigots similar to nozzles that exude silk threads by muscle contraction.
Spiders molt or shed their outer covering several times a year to accommodate growth. Males reach maturity after the last molt late in the summer, mate, then die. Females lay eggs which survive in a cocoon until spring then die or survive the winter covered by leaves.
Spider silk is composed of protein which stiffens upon leaving the spinnerets. A spider can construct a web in 30 minutes using 20 meters of thread in complete darkness. Web construction begins when the spider spins a long thread that catches a breeze until it attaches to a branch or blade of grass. Next, the spider walks to the middle of the thread where it fixes a new thread, then drops spinning a thread to reach a solid support fixing the new thread, thus creating two joined threads fixed peripherally at three points. The outer frame, radii and spiral threads are created when the spider walks on existing threads to spin a new thread, carrying it with its hind legs so it does not stick to the thread it walks on. The final spirals are spun from sticky silk threads to hold entangled prey.
Now, I admire the spider and I hope you can too.