Carnivorous Nights (31 page)

“No stripes, no tiger,” Alexis said dismissively.

Still, when we looked out at the green forests and jagged hills, the landscape was infused with an extra charge. Danny's tale had added an element of uncertainty.

We were driving up into the foothills of the Great Western Tiers. This region was another of Tasmania's tiger hot spots—rife with sightings and not far from where James Malley had found his tiger tracks in 1971. Jim Nelson from the Field Naturalists Club had told us that the area harbored some other elusive creatures. There was no doubt they existed, but we would have to go underground to see them. We decided to take a detour from our tiger search.

Mole Creek Karst National Park encompassed 5.2 above-ground square miles. Below its surface were more than two hundred caves, hundreds of miles of passageways, plus subterranean rivers, sinkholes, and blind valleys.

As we got nearer to the caves, we entered a lush forest cut by a stream and filled with spreading tree ferns. The invisible world below us was carved out of 400-million-year-old limestone. Much of the erosion had been caused by meltwaters from the last Ice Age infiltrating the bedrock. The caves were still in the process of being formed. Rainwater from the terrestrial realm leached through the plants on the surface, turned acidic, and drop by drop melted and molded the soft limestone beneath our feet.

Our destination was Marakoopa Cave. There, a ranger named Brooke Cohn would serve as our ambassador to the creatures from below. We met her at the ranger station and observed that she was tall and wiry, with short, curly blond hair. For someone who spent so much time underground, she was remarkably tan and attractive.

Walking toward Marakoopa, Brooke explained there were different zones of life in the cave. Subterranean species were adapted to live at different depths and some lurked right outside the entrance. The cave's entryway was blocked with a steel door to control the flow of people in and out. In front of it, Brooke pointed to one of the creatures inhabiting the cave's outermost zone. “She's all legs.”

The creature was a female spider the size of Brooke's hand. From an inch-long body, her legs stuck out three inches on each side. And she was closely guarding her egg sac, a white round ball dangling from a short silk thread in a rocky crevice. “That's a Tasmanian cave spider, an ancient species.” Her closest relatives were spiders that lived in South America,
dating from the time of Gondwanaland millions of years ago, when all the southern continents were connected.

As we explored the moist folds in the wall of limestone, we realized we were looking at some sort of nursery, as there were at least three egg balls, each guarded by a giant spider. The egg balls were an inch in diameter and dotted with brown tidbits—the mother spiders decorated them with tiny pieces of rotting wood for camouflage. They would guard the egg balls for eight months before their spiderlings hatched.

The male cave spiders, Brooke explained, had significantly smaller bodies. And on their second pair of legs, the males had special hooks that they used to hold the female spider's fangs open during mating. Without the hooks, the males might be eaten before mating successfully occurred— and they often were eaten right after. During the act of mating, a female's fangs dripped with venom.

To find their way in the dark, cave invertebrates are endowed with inordinately long legs and antennae. (The male cave spider's legs can reach seven inches in length.) They can also go a long time without eating— since it's often tough to get a meal in a dark cave where nothing grows except fungus—and as a result they live a long time. Scientists believe the Tasmanian cave spider may live for decades.

Brooke unlocked the door to the cave and a stream of cold air hit us. Because the temperature in the cave is always between 48 and 52 degrees Fahrenheit, a differential builds up on hot days and high-pressure cool air rushes out the cave entrance. The day we visited it was nearly 90 degrees out, and the cave's exhalation was so strong it was hard to pull the door closed. It felt like being run over by an invisible train.

Once we were inside, Brooke flicked on a light that illuminated a cave chamber. It was enormous—the size of a ballroom—with rust brown stalactites hanging down from the rocky ceiling and flowstones creating the illusion of frozen waterfalls. The chamber's far wall was smooth, forming a half-dome-shaped amphitheater, and we heard the roiling sound of an unseen, underground stream beneath us. This chamber, Brooke said, was in the transition zone. Under natural conditions, no light penetrated, though it was slightly influenced by outside temperature and humidity.

“Ready?” she asked.

Brooke switched off the light and we were enveloped in darkness. The sound of the rushing subterranean stream and the wind howling through distant, unseen cave passages grew louder.

“Give yourselves some time,” Brooke said from the dark. “Your eyes will adjust.”

Overhead, pinpoints of burning blue light began to appear. It was as if, instead of being underground, we were watching stars appearing one by one in the night sky. Or back at the Hayden Planetarium, watching the space show.

“Glowworms,” said Alexis.

“Hundreds,” Brooke confirmed. “Thousands maybe.”

The glowworms were congregating on the rocky ceiling of the natural amphitheater that curved over the underground stream. They were actually not worms, Brooke explained, but the larvae of a tiny fly.

“We've got one species of glowworm in Tassie—they're endemic. They only live in wet caves or terrestrial wet environments—and they're just above us here.” The species was
Arachnocampa tasmaniensis
, which means Tasmanian spider grub.

Although not related to spiders any more than they were related to worms,
A. tasmaniensis
had a spider's ability to make sticky silk strands. “They suspend themselves from the undersurface of the cave's ceiling by threads, and it's like they're in a little sleeping bag”—a hollow tube made of silk and mucus—“and from there they drop down multiple threads of silk—very sticky, mucousy fishing lines to catch their prey. That nice dark blue glow—it's them burning their waste products, but it also attracts prey. The brighter the glow, the hungrier they are.”

The glowworms' prey is flying insects. The larvae of mayflies, stoneflies, and caddisflies are aquatic and sometimes get swept from terrestrial rivers into underground streams. When these insects emerge from their larval stage and turn into flying adults, they find themselves stuck in the dark. Then, when they see the glowworms' lights, they head right up— and get caught in the sticky fishing lines. The glowworms simply reel them on up.

The glowworms themselves stay in their larval incarnation for up to eighteen months. When they finally turn into flying adults, they have only three or four days left to live. “They don't eat—they don't even have
mouthparts. All they do is go out and reproduce,” Brooke said. “And they do it carefully, because every one of those glowworms has thirty to fifty threads of silk. And often they get caught in their own fishing lines.”

With each passing second—as our pupils dilated—more and more glowworms became visible. There was something creepy about the illusion—these grubs and their sticky little threads so effectively posing as a starry night. The lights were beautiful, intoxicating, and we wondered if people ever became mesmerized by the glowworms—thinking they were sleeping under a starry sky, falling into a cave dream, and never waking up.

Certainly, some animals came in and never came out. “As you can hear, we've got a stream going underneath. That brings other cave fauna in, accidentals,” said Brooke. “Often in floods, we get platypus and trout that have been pushed through from about a thousand meters up, from the Great Western Tiers. It's very rare, but they end up down here. And we also get wallabies and wombats that fall through sinkholes. They die. They fall into the water and eventually they decompose—and encourage more insect life in the cave.”

After the wind pushed us out the cave door and back into the world of the living, Brooke decided she wanted to show us something else— a wilder cave in a different part of the karst system. As we drove on a narrow, winding road through more wet eucalypt forest, Brooke told us a little more about herself. She was a teacher during the school year—she educated autistic children—and worked as a ranger with the Parks and Wildlife Service during the summer. She lived in a small commune called Platypus Bend. They didn't have electricity and grew their own food. She preferred to live off the grid.

On the drive over, Brooke saw a dead animal in the middle of the road. It was a young devil—badly mashed.

“It's sad, you know. I saw him last night.” Her face creased with concern.

“You recognize it?”

“Yeah, you just get a feel for them, their size and markings.”

Brooke stopped to move it to the side, and Alexis jumped out, too. The animal's entrails were splayed out across the blacktop, and its nearly liquefied carcass was crawling with flies. Alexis pushed his camera right up next to the body. “Could I get you to pose with that?” he asked. Brooke
didn't seem to hear him, but he was able to snap her picture as she used a plastic shopping bag for a glove and moved the body into the brush.

Then we got back on the road. “I'll take you to a wild cave called Snail Space, just to give you a feel for it,” she said. We parked by a sign that read “PETS AND FIREARMS NOT PERMITTED,” and walked into the woods. The cave's entrance was a vertical slit in the ground, with ferns dripping down over the top and dogwood trees, mosses, and lichens growing all around it. A muddy, two-foot-wide chute led down toward the rocky entryway. One by one, with Alexis in the lead and gripping a small flashlight between his teeth, we slid down the hole.

When we reached the narrow entrance, we put out our hands to brace ourselves against the rock—and felt a tickling sensation. Something was moving. As the hair rose on the backs of our necks, we turned our heads. The rocky wall was heaving with brown insects. Tiny brown eyes, crawling legs, and probing antennae.

“Motherfucker!” we heard Alexis whisper from inside the cave.

“Careful of the cave crickets,” Brooke warned.

The cave crickets were only an inch long and didn't have fangs or stingers. They weren't threatening-looking. It's just that there were so many of them, and their antennae were absurdly long—as long as four times the length of their bodies. We experienced a complex emotion: an ancient fear of creepy-crawlies combined with concern that we might squash a rare cave beast.

As we descended through the rocky slot, we tried not to touch or hold anything. It was disconcerting plunging deeper and deeper into darkness, not knowing what might be on either side.

After a few more feet, the rocky slot opened into a small chamber. The four of us barely fit inside—and when Alexis shone his flashlight on the stone walls and ceiling, it illuminated cave spiders and hundreds of crickets.

This area of the cave was called the twilight zone due to the fact that it was not completely dark. When we looked back toward the entryway, we saw a wafer-thin slit of light. That was all that remained of the outside world.

The crickets, Brooke told us, were endemic to the caves of northern Tasmania, usually living near cave entrances in dense colonies. They were considered trogloxenes (
troglo
= cave,
xeno
= strangers), because they
sometimes went out. Primarily scavengers, the crickets ate moss growing near the cave entrance and dead fellow invertebrates.

We stepped backward to get a broader view of the chamber and suddenly felt the floor—mud, gravel, and rock—giving way beneath our feet.

For a moment, we lost our equilibrium and began falling backward into a deep, lightless hole—filled with God knows what. We grabbed hold of the walls of the rock chamber and, regaining our balance, found ourselves holding hands with what we prayed were cave crickets. From behind, we heard a small rock tumbling down the hole: PLING, PLING, PLING, PLING, PLING, PLING, PLING. Hello? We didn't hear it land. Gingerly, Alexis sidled forward and shined his flashlight down. If there was a bottom we couldn't see it.

“Careful,” Brooke said. “There's a drop there.”

We had nearly become accidentals, like the unwitting wombats and wallabies that fell down sinkholes and ended up becoming food for famished cave creatures. We looked at the crickets in a new light. They were scavengers, weren't they?

“What's down there?” Alexis asked.

Brooke explained that if you went far enough into the caves, you reached the deep zone where no light penetrated and troglobites lived. In the deep zone, it was humid and the temperature was constant no matter what the season. Troglobites had evolved to live in these odd conditions. They often were pale or without pigment. Sometimes they had no eyes. Since no plants could grow in this lightless environment, being an herbivore wasn't an option. Deep zone creatures had two choices: eating each other or waiting until something fell in that they could scavenge upon.

One of the creatures that was beyond our sight was the cave pseudoscorpion (
Pseudotyrannochthonius typhlus
), a tiny stingerless eightlegged arachnid that over thousands of years of cave life had lost its eyes and pigment. What the pseudoscorpion got in exchange for its eyes and coloration was an enhanced sense of smell, long sensory hairs on its legs with which it could sense the slightest vibration, and a set of rangyarmed pincers for reaching out and grabbing any meat that might fall its way. The pseudoscorpion was a super-endemic, meaning that it only lived in the Mole Creek cave system—and as far as scientists knew, only in a few of those. Like most deep zone creatures, it couldn't survive in
the open air. It was listed as rare under Tasmania's Threatened Species Protection Act.

We pondered the pseudoscorpion's genus name:
Pseudotyrannochthonius.
(
Pseudo
= false,
tyranno
= fierce. And
chthonius
?) Chthonius had several lives in Greek mythology. In one story, Chthonius was one of the black steeds that powered Pluto's chariot from the underworld and back. In another, he was a warrior that sprang from the earth and attacked anyone in his path.