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The Honolulu Advertiser
Posted on: Wednesday, January 25, 2006

Piggyback baby spiders photographed in cave

By Jan TenBruggencate
Advertiser Science Writer

Two hatchlings hitch a ride, matching tooth-like appendages on their claws to hairs on the mother's back. The baby spiders spend about 24 hours riding on the mother's back before going off on their own.

GORDON SMITH | U.S. Fish and Wildlife Service

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A blind Kaua'i cave wolf spider carries her egg sac under her, waiting for her babies to hatch.

GORDON SMITH | U.S. Fish and Wildlife Service

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KOLOA, Kaua'i For the first time in the wild, scientists have photographed one of the unusual characteristics of the blind Kaua'i cave wolf spider: a mother carrying her newly hatched young on her backs.

The endangered species, known only from caves and crevices in the lava of the Koloa region of south Kaua'i, live out their lives in the underground darkness and have evolved in a special way. While their surface relatives have large eyes, these hunting spiders have no eyes.

"This unique eyeless wolf spider is the most remarkable cave species in Hawai'i," said Bishop Museum entomologist Frank Howarth, in text prepared for the announcement.

But that's not all, he said.

"Besides being perfectly adapted to life in the dark lava tubes of Kaua'i, like their big-eyed surface relatives, cave wolf spiders share a special adaptation their spiderlings have a row of comb-like teeth on their claws that perfectly match the spaces on the multi-branched hairs found on the mother's back. This match allows the spiderlings to hold on for safe transport and protection by the mother."

Howarth discovered the spiders in south Kaua'i caves in the early 1970s, along with another cave creature, the shrimp-like Kaua'i cave amphipod. Both are now on the U.S. endangered species list.

Botany graduate student Wendy McDowell, of Kekaha, Kaua'i, has been conducting monthly surveys of several caves, checking on the two species. She was in such a cave in November 2005 with U.S. Fish and Wildlife Service biologist Gordon Smith when they found a female spider whose egg sac had just opened. Two baby spiders had just climbed up on the mother's back; others were still in the sac, working to be born.

"We could see their little legs moving," McDowell said. While Howarth had watched the process in his laboratory, this was the first time it has been reported in the wild.

McDowell said it is not known how often the spiders reproduce, or whether particular environmental conditions can improve their reproduction rates. She said the spider birth that she and Smith witnessed occurred during a peak in the population of the cave amphipods, which are a food source for the spiders.

"Amphipod numbers were higher than we've observed in the past. We don't really know why, but one suggestion is that the previous year was a very wet year, and it may have produced a bigger food impact for them," she said. "But that's just speculation. It could also be a regular seasonal thing. We haven't been observing them regularly long enough to know."

Amphipods feed on vegetable matter underground, including debris washed into caves and material that grows there, such as the roots of surface plants that reach down into the subterranean areas.

One of McDowell's research objectives is to go to caves where the creatures no longer exist and re-create a suitable ecosystem.

The wolf spiders can fit on the surface of a quarter. The amphipods are much smaller, less than half an inch long. Researchers believe that the main threat to their survival is destruction of their cave ecosystems or their alteration.

Planning and zoning agencies have required the protection of spider and amphipod habitat, and Fish and Wildlife Service biologist Lorena Wada said landowners whose properties include the two species have been supportive of research access to the caves and the protection of the habitat.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.