No one had ever photographed a baby Kauai wolf spider being carried on its mother's interlocking back hairs until two Hawaii scientists caught the shot.

The endangered Kauai wolf spider is rarely seen, and the spiders themselves are blind. Researchers had previously known that the spiderlings use a row of teeth on their claws to grasp their mother's back.

But they had never been able to capture the moment.

The pictures were taken by U.S. Fish and Wildlife Service biologist Gordon Smith. In November, he and graduate student Wendy McDowell found a female spider whose egg sac had just opened.

"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," said Bishop Museum entomologist Frank Howarth in a prepared text. "This match allows the spiderlings to hold on for safe transport and protection by the mother."

McDowell has been conducting monthly surveys of several caves to check on the Kauai wolf spiders and another endangered species, the Kauai cave amphipod.

She and Smith were investigating a cave in November when they found a female spider whose egg sac had just opened. Two baby spiders crawled onto the mother's back while others waited in the sac to be born.

"We could see their little legs moving," McDowell said.

Howarth, considered by many to be the leading expert on the Kauai cave wolf spider, said he had seen the birthing process in his laboratory. But this was the first time it had been reported from the wild.

McDowell said the birth occurred during a peak in the population of cave amphipods, small crustaceans, 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.

Little is known about the wolf spiders, which were first discovered in 1971 in the lava tubes and cave-bearing rock in Kauai's Koloa Basin. They have only been found in five caves within the basin.

The spiders can fit on the surface of a quarter. They don't have any eyes, and they hunt by sensing chemical compounds on the ground. Wolf spiders stalk and attack their prey instead of weaving webs.