Once We All Had Gills: Growing Up Evolutionist in an Evolving World

5. In the Natural World

49 In the Natural World Creatures I was aninveterate naturalist. EachyearI anxiously awaited the returnof spring(and,truthfully,theendofthetime-crawlingendlessschoolyear). I felt a strong curiosity and an intense attraction for the look and feel of natural forms and creatures, the stranger the better. At various times my interests settled on hunting salamanders, insects, turtles, snakes, and fossils in the forested hills near our house. I had read that snakes had no eyelids, so I had to look a snake in the eye. Sure enough, their eyes are coveredbytheclearwindowofasinglemodifiedscaleandcan’tbeclosed even in sleep. All snakes are carnivores. I kept snakes and watched them feed using independently attached lower jaws armed with sharp, curved teeth. A snake engulfs its prey by walking each jaw alternately down its victim’s body, and there is no escape once a snake begins to swallow. It happened to me. I was handling a middling sized garter snake, about eighteen inches long and about as thick as my index finger. It bit the tip of that finger and held on. This posed a quandary to both of us. The snake couldn’t let go because of its recurved teeth, so it began to work its jaws up my finger, committing itself to swallowing a nearly full-sized human–a new frontier for a garter snake. I carefully disengaged its independently movable lower jaws, and slid my finger free without hurting the snake. Fortunately, its upper jaws hadn’t secured much of a hold because my fingernail was in the way. I got to keep a few tiny punctures as souvenirs. five 50 Becoming a Naturalist This story suggests something of the vagaries of natural selection. The feeding mechanism of snakes is highly evolved and has served them well, yet evolution can’t look ahead to situations in which holding on and swallowing might be fatal to an individual snake. I once stumbled upon a strange-looking dead snake. The back half of another snake protruded from its mouth. It had tried to swallow a snake of almost equal size. I pulled the swallowee out. Its head had been digested, but not fast enough to save the consumer from suffocating. There are also documented cases (at least in captivity) of hungry snakes that mistakenly attack their own tails. Once their teeth have fastened on they can only move forward, which means eating their own bodies to the point where the body can’t bend any tighter–or having the good fortune of being rescued by a veterinarian. Liking drama, I watched orb weaver spiders capture insects in their webs, wind them in silk, and then inject them with venom. They later inject a cocktail of digestive enzymes and feed leisurely on the liquefied insides of the insect. More primitive spiders bite first and then wrap dinner up to marinate. On slow days I’d help out by providing the prey to see how different insects fared. Large beetles and grasshoppers simply muscled their way out by breaking the web. The biggest question we kids puzzled over was how the spiders themselves could walk around on their webs without becoming stuck. This conundrum was well solved by studiesshowingthatspidersmakedifferentkindsofsilk.Radialstrands, made first in building an orb web, are not sticky. The spiral silk put down afterward is the sticky trap for insects. The spiders simply keep their feet off the sticky strands. It’s the females that make the spectacular silken death traps. By end of summer they have become fat and ready to mate. Thatthewords“spider”and“sex”couldbeassociatedinonesentencehad not occurred to me. It was only years later that I first saw a little eightlegged romantic male spider woo a big greenish brown female Neoscona orb weaver who built her web each day from the eaves of our garage. The scrawny males timidly hang out at the edge of a web and pluck the radial strands hoping to convince the female to accept them as sex partners rather than dinner. The job, once an ardent male is accepted to her lair, is to pass on his genes by successfully mating with his ladylove before she changes her mind. It’s often not really a choice. In some species, In the Natural World 51 successful male spiders go to their reward as postcoital snacks for their unsentimental mates. One year’s enticement was salamanders. These small creatures were common in Pennsylvania woodlands if one was willing to spend...