Spider, No-eyed Big-eyed Wolf

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Spider, no-eyed big-eyed wolf

Adelocosa anops

phylum: Arthropoda

class: Arachnida

order: Araneae

family: Lycosidae

status: Endangered, IUCN Endangered, ESA

range: USA (Hawaii)

Description and biology

The no-eyed big-eyed wolf spider, also known as the Kauai cave wolf spider, is a troglobite—a species that lives only in caves. It has a body length of 0.39 to 0.78 inch (0.99 to 1.98 centimeters). Its head and thorax (body segment between head and abdomen) are fused or united. This body part is called the cephalothorax (pronounced se-fa-la-THOR-ax), and it is light brown or orange. The spider's bristly legs are also orange in color. The abdomen is dull white.

All other spiders belonging to this family have large, well-developed eyes. The no-eyed big-eyed wolf spider is so-named because it is blind. To capture prey, wolf spiders do not spin webs like other spiders; most actively stalk and over-take other small invertebrates (animals with no backbone). The sightless no-eyed big-eyed wolf spider crawls slowly through the cracks and crevices in caves, finding its prey through its senses of touch, smell, and taste. It has large fangs with which to inject and subdue its prey with its venom (poison). The spider's usual food is the Kauai cave amphipod, a tiny crustacean that lives in the same caves as the cave wolf spider. The two species have a predator/prey relationship: the amphipod gets its nutrients from the rotting vegetation on the moist rocks of the humid cave environment, and the spider then feeds on the amphipod.

Females of this species lay only 15 to 30 eggs in a clutch (number of eggs produced or incubated at one time). They carry the egg sac inside their mouths until the eggs hatch. At that time, fully developed and unusually large infant spiders emerge. The newborn offspring stay with their mother for a few days, riding on her back, until they are ready to hunt on their own. The life span of an adult no-eyed big-eyed wolf spider is at least six months.

Habitat and current distribution

The no-eyed big-eyed wolf spider inhabits only the deep areas of Koloa caves, located on the southeast coast of Kauai Island in the Hawaiian Islands. The spider is found in the caves as well as in small cavities attached to the cave that humans cannot reach.

In its extremely limited cave ecosystem (all living things and their environment), the spider requires specific conditions. The humidity in the cave must be a constant 100 percent, the air must be stagnant (still), and the air temperature must be between 75° and 80°F (24° and 27°C). The caves must also have the right type of woody vegetation for the spider's prey, the Kauai cave amphipod, to eat. The no-eyed big-eyed wolf spider is known to exist only in six caves in the Koloa area.

History and conservation measures

The no-eyed big-eyed wolf spider, along with its prey, the Kauai cave amphipod, was discovered in the beginning of the 1970s and for decades was known to exist in only four caves. Two more caves with populations of the species were found in 2002. The species is limited to a small and very specific area and has become endangered because of the deterioration of its habitat. The caves in which these spiders live are in a very popular and developed resort area of Hawaii. Tourism and urban growth are constant pressures. Water is already scarce in the area, and natural water sources have been diverted to meet the needs of tourist facilities and urban areas. Without a constant supply of seeping water, the caves inhabited by the spider will dry out.

Runoff from urban areas can pollute the groundwater with pesticides and other toxic (poisonous) chemicals. Runoff from nearby farms has already ruined the largest lava cave in the area: it became covered with waste residue from sugar cane production. Human visitors can also destroy these caves by trampling, littering, smoking, vandalizing, and altering the climate by merely entering the caves.

After the no-eyed big-eyed wolf spider was given endangered status under the Endangered Species Act (ESA) in 2000, a federal court ruled that the U.S. Fish and Wildlife Service (USFWS) should determine a critical habitat area for the spider—an area considered necessary to the conservation of the species that requires special management and protection. Critical habitat designation does not create a wildlife refuge and does not ban human activities in the area. Rather, it ensures that all federal agencies check with the USFWS about any activities they authorize in the area. On April 9, 2003, the USFWS designated 272 acres (110 hectares) in southern Kauai as critical habitat. One year earlier, the agency had proposed that 4,193 acres (1,698 hectares) should be designated as critical habitat, but changed the proposal because it would have been very costly to private landowners in Hawaii.