To move your spider, click on the web where you want him to go. To make your spider spin a strand of web, drag your mouse between two existing web strands (or a branch). Click on the insects that get caught in your web to eat them. This will earn you points, add to your spider's web supply, and keep your life meter up. If the spider's life meter reaches zero, he dies and the game is over.
Experience life as a hungry spider at night. Can you complete the final achievement and eat a bat?
There is a lot of strategy involved in maintaining your web to get it to a point where you can catch the bat. Saving bugs to eat for later is a great idea, but too many will weaken your web. A big web will help you catch more bugs, but will also be harder to maintain.