How does a spider's web catch a fly?

Have you ever brushed past a spider web and felt thin threads tickle your face? Those threads feel as light as a whisper. Yet a fly that flies into them cannot get away. So how does a spider's web catch a fly?

Every thread in the web is silk, which means a thin, strong thread that a spider makes inside its own body. One silk thread is thinner than a hair on your head. Even so, silk is strong enough to hold a fly without snapping.

Now picture a fly zooming across the garden, buzz, buzz. Busy looking for something sweet, it flies straight into the web. A fast fly hits hard, like a ball thrown into a net.

Instead of snapping, the silk stretches. The threads sag and give, like a trampoline when you jump on it. Because the silk stretches, the fly does not bounce off, and the web does not tear.

Along the threads that circle round and round the web sit droplets, which means very small drops of sticky glue. In the morning light they shine like beads on a necklace. The droplets are there to grab whatever touches them.

While the web still sways from the bump, the droplets grab the fly's legs and wings. They hold on the way tape holds paper to a wall. The fly kicks and buzzes, trying to pull free. What do you think happens each time it wiggles?

Each wiggle pushes another leg or wing against more sticky threads. More droplets grab hold, so the fly gets more stuck, not less. Every kick leaves the fly held tighter than before.

Soon the fly is stuck from head to wing and can barely move. The web caught it without the spider chasing it at all. All the spider had to do was wait nearby.

Let's remember two words: silk and droplets. When a fly zooms into a web, the stretchy silk soaks up the bump so the fly cannot bounce away, and the sticky droplets glue it in place.

Next time you see a web sparkling in a garden, you will know how it catches its dinner. Sleep tight, little web watcher.