Structures built by animals, often called animal architecture, are common in many species. Examples of animal structures include termite mounds, wasp and beehives, burrow complexes, beaver dams, elaborate nests of birds, and webs of spiders. Often, these structures incorporate sophisticated features such as temperature regulation, traps, bait, ventilation, special-purpose chambers and many other features. They may be created by individuals or complex societies of social animals with different forms carrying out specialized roles. These constructions may arise from complex building behaviour of animals such as in the case of night-time nests for chimpanzees, from inbuilt neural responses, which feature prominently in the construction of bird songs, or triggered by hormone release as in the case of domestic sows, or as emergent properties from simple instinctive responses and interactions, as exhibited by termites, or combinations of these. The process of building such structures may involve learning and communication, and in some cases, even aesthetics. Tool use may also be involved in building structures by animals. Building behaviour is common in many non-human mammals, birds, insects and arachnids. It is also seen in a few species of fish, reptiles, amphibians, molluscs, urochordates, crustaceans, annelids and some other arthropods. It is virtually absent from all the other animal phyla. Functions Animals create structures primarily for three reasons: to create protected habitats, i.e. homes. to catch prey and for foraging, i.e. traps. for communication between members of the species (intra-specific communication), i.e. display. 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. Protected habitats Predators are attracted to animal-built structures either by the prey or its offspring, or the stored caches of food. Structures built by animals may provide protection from predators through avoiding detection, by means such as camouflage and concealment, or through prevention of invasion, once predators have located the hideout or prey, or a combination of both. As a last resort, structures may provide means of escape. Among the structures created by animals to prevent predation are those of the paper wasps, Polistes chinensis antennalis. The nests of these wasps contain “defensive structures”, which are formations built onto or inside of the nest to prevent predation. New nests are