Spider Spider Spiders (order Araneae) are air-breathing arthropods that have eight legs and chelicerae with fangs able to inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other orders of organisms. Spiders are found worldwide on every continent except for Antarctica, and have become established in nearly every habitat with the exceptions of air and sea colonization. , at least 45,700 spider species, and 113 families have been recorded by taxonomists. However, there has been dissension within the scientific community as to how all these families should be classified, as evidenced by
Structures built by animals amphibians, molluscs, urochordates, crustaceans, annelids and some other arthropods. It is virtually absent from all the other animal phyla. Animals create structures primarily for three reasons: Animals primarily build habitat for protection from extreme temperatures and from predation. Constructed structures raise physical problems which need to be resolved, such as humidity control or ventilation, which increases the complexity of the structure. Over time, through evolution, animals use shelters for other purposes such as reproduction, food storage, etc. Predators are attracted to animal-built structures either by the prey or its offspring, or the stored caches of food. Structures built by animals