Carla Rhone, age 11, of Williamsport, Pa., for her question:
DO SPIDERS HAVE NOSES?
A busy spider must be able to dodge her enemies and also catch enough flighty flies to fill her fat tummy. Obviously she must know exactly what's going on in the neighborhood. Chances are, she has eyes in the top of her head. When an
insect gets trapped in her web, she feels vibrations from the silken threads. And, though she has no human type nose, she also has a keen sense of smell.
A spider breathes through a slit in her fat round tummy. The air seeps in, wanders through a network of tubes and brings oxygen to the cells inside her body. Used air seeps out through the same doorway. This sort of nose is handy for breathing, but it is no use for sniffing.
Actually, the spider can smell with many parts of her body. Here and there, under the skin, she has mini wads of special cells that can sense odors and maybe also flavors. These are connected to superfine nerves that flash messages to her brain.
Most of her smelling is done by a pair of sensitive feelers, one on each side of her amazing mouth. They are called pedipalps and they look like small legs, each with six joints. The hairs and sensitive cells in her pedipalps detect smells and most likely flavors in her food and in anything else she touches. She has more of these tiny sense organs in her spidery legs and other parts of her body.
There are about 30,000 different spiders and each type has her own way of life. All of them have breathing slits in their abdomens and all of them smell through similar sensory cells. But some have keener eyesight than others and some are totally blind. Some have two tiny eyes, some have four and some have eight on top of the head.
All spiders are very sensitive to trembling vibrations, especially those that trap their victims in silken webs. When the orb spider finishes her splendid rough web, she goes off and waits in a nearby shady corner. One or two of her eight legs rest lightly on several of the long threads of her web.
When a fly zooms into her sticky net, naturally he struggles to get free. But this only makes the tangle worse. It also jogs and vibrates all the silken threads. The waiting spider feels the vibrations and comes striding out to dinner ¬taking care to step only on the nonsticky threads.
The clever spider can sense strong and weak vibrations. When the vibrations are very weak, she decides that the captive is too small for dinner and usually ignores him. When the vibrations are very strong, she knows the victim is large and may be dangerous. She may cower in her corner or cut him free to save her web. This goes to show that the spider is very well informed about what goes on around her.