United States Fish and Wildlife Service list of threatened and endangered arthropods species may be treated as endangered or threatened if it resembles in appearance a species which has been listed and enforcement personnel would have difficulty distinguishing between the listed and the unlisted species; if the effect of this difficulty is an additional threat to the listed species; and if such treatment of the unlisted species would improve protection for the listed species. United States Fish and Wildlife Service list of threatened and endangered arthropods List of threatened and endangered arthropods, including insects, arachnids, and crustaceans under the United States Endangered Species Act as of October 2013. Key to Listing Status
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