How does a spider evaluate the size of an intruder? Let us find out.
Things Required:
String
A partner
Directions:
Stretch the string between two stationary objects. A door knob and a table leg are good choices. At one end of the string, gently place the tips of your fingers on top of the string. Take your partner to pluck the opposite end of the string while you look away. You do not want to see how firmly the string is being plucked. Your partner should pluck the string with varying degrees of firmness: gently to very firm.
This Is What Happens:
You will be able to feel the varying degrees of vibrations of the string with your fingertips.
Science Behind It:
When the string is plucked at one end, it causes the entire string to vibrate. A gentle touch produces a weak vibration, and a more aggressive plucking causes the entire string to vibrate briskly. Spiders feel the vibration of their web. The web acts like a telegraph line. When the web shakes, the spider senses the movement because it has sensory hair on its legs. If the vibration is very weak, the spider ignores it. Very large vibrations could mean a prey that would injure the spider, so it often hides or cuts the strand. A medium vibration lets the spider know that the intruder is small enough to catch for dinner and it rushes towards the source of vibration to invite the visitor to stay awhile. The spider quickly wraps the trapped visitor in strands of silk before it can escape from the sticky web.