Endangered spiders

An endangered species is “a species at risk of extinction because of human activity, changes in climate, changes in predator-prey ratios, etc., especially when officially designated as such by a governmental agency such as the U.S. Fish and Wildlife Service” [http://www.Dictionary.com] . A spider is a member of the order Araneae, one of many orders within the class arachnida, meaning it has a body consisting of two segments, a cephalothorax and an abdomen, as well as eight legs. All spiders are predators that feed off insects, and some larger species have been known to catch small reptiles, birds, and amphibians (Levi and Levi, 2002).Until recently, insects and arachnids have not been considered for inclusion on threatened and endangered species lists. It was not until 1994 that most invertebrates were even recognized as being just as vulnerable as other fauna. It is because of this that there are very few species of spiders listed as threatened or endangered and many are simply classified as “undetermined” [http://www.iucnredlist.org] .

Listed species

While few organizations agree completely on which spiders are endangered or threatened, a few commonly listed species are the Spruce-fir moss spider, the Dolloff cave spider, the Great Raft spider, and the Kauai cave wolf spider.

Spruce-fir moss spider ("Microhexura montivaga")

This species is federally listed as endangered under the Endangered Species Act of 1973. This spider resembles a tiny “tarantula” with adults measuring in at only 2.5 to 3.8 millimeters. This particular species inhabits high-elevation forests in western North Carolina and eastern Tennessee. The species is extremely vulnerable to desiccation, causing it to shelter in damp shady areas such as shaded moss. The spider builds a tube shaped web between the moss and a rock or fir tree (Fish and Wildlife service, 1995), hence the name.

Dolloff cave spider ("Meta dolloff")

While not listed as endangered, this spider is considered to be vulnerable to extinction. Much larger than "Microhexura montivaga", this spider ranges in size from 10 to 15 millimeters. This species makes large orb shaped webs at the entrance of caves and as of 2001 has only been found in caves located in Santa Cruz, California (Ubick, 2001).

Fen Raft spider ("Dolomedes plantarius")

The number of Fen Raft spiders has declined so much that one of only two populations is close to extinction. These two remaining populations can be found only in Great Britain, making the Fen Raft one of its largest spiders and rarest animals. This spider is a semi-aquatic species and its dependence on water may have led to the population's decline. The information on the Fen Raft spider is very recent and due to a lack of historical records, the level of decline cannot be accurately measured (Smith, 2000).

Kauai cave wolf spider ("Adelocosa anops")

This spider is found only on the Hawaiian island of Kauai. In fact, as of 2006 this species can be found in one cave on that island and only 16 to 28 individuals have been encountered. Compared to other spider species, the Kauai cave wolf spider has a low reproductive rate and, due to habitat constraints, has little access to food sources (Fish and Wildlife service, 2006). This spider is one of the largest documented cave-dwelling organisms measuring up to a massive 8 centimeters. Because it spends its life in the darkness of a cave, this spider has no need for sight and is therefore completely eyeless (Krajick, 2001).

Reasons for population declines

Because of their small size and relatively fast reproductive rate, it is easy to believe that spiders are not as vulnerable to extinction as the well known megafauna. The references mentioned indicate otherwise. Spiders are extremely vulnerable to a wide variety of environmental factors ranging from food abundance to pesticide use to habitat destruction. The reason for each population's decline is very species-specific and cannot be generalized.

References

* Krajick, K. 2001. "Cave Biologists Unearth Buried Treasure". "Science" magazine. Vol. 293. Pp. 2378-2381.
* Levi, Herbert W. and Lorna R. Levi. 2002. "Spiders and Their Kin". St. Martin's Press. New York, U.S.
* Smith, Helen. 2000. "The status and conservation of the fen raft spider (Dolomedes plantarius) at Redgrave and Lopham Fen National Nature Reserve, England". "Biological Conservation". Vol. 95. Issue 2. Pp. 153-164.
* Ubick, Darrell. 2001. "Cavernicolous invertebrates of Cave Gulch, Santa Cruz County, California". Department of Entomology, California Academy of Sciences. San Francisco.
* U.S. Fish and Wildlife Service. 2006. "Recovery Plan for the Kauai Cave Arthropods: the Kauai Cave Wolf Spider (Adelocosa anops) and the Kauai Cave Amphipod (Spelaeorchestia koloana)". U.S. Fish and Wildlife Service. Portland, Oregon. 64 pp.
* U.S. Fish and Wildlife Service. 1995. "Endangered and Threatened Wildlife and Plants; Spruce-Fir Moss Spider Determined To Be Endangered". Federal Register. Vol.60. No. 24. Pp. 6968-6974