Love 'em or hate 'em, you've got to admit that spiders are some pretty impressive, well-equipped animals. They have a top-notch sensor array, a built-in construction set, a heavily armored body and a highly effective venom-injection system. How many other creatures can claim that?

Photo courtesy Steve & Miriam Clark
A lynx spider in the Australian Outback

These remarkable adaptations have made spiders some of the most successful carnivores in history. In their 400 million years of existence, they've spread over every continent and mastered nearly every environment on Earth. Today, there are about 40,000 known spider species, and potentially thousands more we haven't discovered yet. This is pretty astounding when you consider that there are only about 4,000 different species in the entire mammal kingdom.

In this edition of HowStuffWorks, we'll find out how these unique animals spin webs, attack prey and walk straight up walls. We'll also look at some particularly interesting spider species, including spiders that swim, spiders that jump from branch to branch and spiders that can kill a person.