Arachnids are a class of invertebrates that belong to the arthropods. Despite similarities to insects, such as an exoskeleton, they are easy to tell apart as they have eight rather than six legs, and have no antennae or wings. The most well-known members of the class Arachnida are, of course, the spiders (order Araneae), but the group also includes scorpions, ticks, mites, harvestmen, and solifuges (also known as camel spiders, wind scorpions, or sun spiders). Several groups have venom glands and use their fangs to inject it to kill prey or enemies.
All spiders produce silk, and most of them use it to make large webs in which to catch prey, although some use it for hunting in other, more creative ways (such as the bolas spider that uses strands with sticky blobs at the end which it swings at flying insects). Pseudoscorpions are another group that produce silk, which they use to create cocoons for mating, moulting or shelter.
![Mamíferos de Argentina, Tomo 1: Marsupiales, Primates, Quirópteros y Ungulados [Mammals of Argentina, Volume 1: Marsupials, Primates, Chiroptera, and Ungulates]](http://mediacdn.nhbs.com/jackets/jackets_resizer_medium/26/266100.jpg?height=150&width=106)
