Spiders are a set of arthropod animals of the Araneae order, very abundant throughout the world and about 45,000 different species are known. They are the most numerous order of the Arachnida class and are distantly related to other groups of arthropods, such as insects. It is also one of the most diverse groups, placing itself as regards the rest of organisms in seventh place with respect to their diversity. Spiders leave their eggs in a silk sack, where there may be about 100 eggs. These can be fixed to the surface, hidden in a net or carried by the female. The presence of sacks fixed inside a house indicates that soon there will be more spiders.