Although spiders are widely feared, only a few species are dangerous to people. Most spiders will only bite humans in self-defense, and few produce worse effects than a mosquito bite or bee-sting. Most of those with medically serious bites, such as recluse spiders and widow spiders, are shy and bite only when they feel threatened, although this can easily arise by accident.

• Spiders have eight legs and mouthparts with fangs that inject venom.
• Their abdomens bear appendages that enable them to spin silk from up to six types of silk glands within their abdomen, which is how they make their webs.
• Spiders can be found on all continents, except Antarctica.