All spiders have fangs and most kinds have venom glands. They use their fangs and venom glands to capture their food. A spider's bite can kill insects and other small animals. A few kinds of spiders are harmful to human beings. In North America, six kinds of spiders harm people, they are - the Brown Recluse, Sac, Black Widow, Brown Widow, Red-legged Widow and the Varied Widow. Four of the Widow females are known to bite humans. The bites of these six spiders often cause mild reactions. Usually a person irritates a spider several times for it to bite you. In Australia, the most dangerous spider is the Funnel-Web with the Red-back, a type of Black Widow spider, also being dangerous
There are more than 30,000 kinds of spiders. Scientists believe there may be up to 50,000 to 100,000 kinds. Some are smaller than than the head of a pin but some are larger than a person's hand. One kind of spider, a South American tarantula is measured at 25 centimetres but that is with its legs extended.