| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
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A Closer Look Cave Creepers
Here I am, wriggling on my tummy through a narrow, dark passage. Lumpy rocks press in on me from all directions, while my partner’s muddy boots flail inches from my nose. The sound of gasping breath seems deafening, and the erratic, bluish flashes from my headlamp confuse rather than guide the way. Cave men, phooey. Who’d want to live in a cave? The answer is literally in my face, as moths flutter haphazardly, always avoiding my grasping fingers. Spider webs gleam white against the gray-brown walls. Today, I am part of a team investigating exactly what lives in Empire Cave, a part of the Cave Gulch system in Santa Cruz County. The California Department of Parks and Recreation has recently taken charge of this system, and has asked us to track down and document its fauna.Life in a cave starts in the “twilight zone,” the interface between the cave and the outside world. There is a fair amount of light, and moisture levels and temperature fluctuate with the seasons. Fallen leaves add nutrients to the ecosystem, and less specialized creatures that can tolerate changing conditions, such as darkling beetles, live here. In Empire Cave, just behind the reinforced concrete cast constructed over its original entrance in a vain attempt to protect it from the Party Animal, chunky Meta spiders the size of kumquats spin their coarse mesh webs. There are also a few moths such as furry, mottled gray-and-brown Triphosa, which use the cave like an apartment, flying out at night to feed on nectar. Tiny fungus flies lift peevishly into the air above the moldy pockets in which they feed. These and other part-time cavers such as raccoons, bats, and bears, spend only a fraction of their lives here. Such “trogloxenes” use caves for temporary shelter, or to complete a part of their life cycle. Dense mats of “cave hair” coat the far wall. They are made up of thousands of harvestmen, or daddy longlegs, in the genus Leiobunum. When they sense a threat, they vibrate synchronously, ever faster, until they all become a single blur. Most predators can see movement in only a narrow range of frames, and at about 90 frames per second the vibrator becomes invisible. Preferring to set up camp in the twilight zone, where birds such as creepers and nuthatches or insect-eating mammals such as shrews search for insect or spider meals, this defense strategy pays off. Harvestmen and other “troglophiles” including Nesticus spiders, smaller relatives of the infamous black widow, may spend their entire lives inside caves but are also found in similar surface habitats—like the “mini-caves” found beneath large rocks. Deeper in the cave, my bustling companions and I reach a large, dark chamber. Around the edges, particularly toward the back of the cavern, percolating water trickles into pockets of moist soil. Tiny, glittering carabid beetles, sinuous red centipedes, and ghost-pale symphylans, like the shrunken phantoms of centipedes, abound here. These thin-skinned critters are prone to drying out and need moisture to survive. The symphylans, many-legged arthropods no larger than a grain of rice, are preyed upon by the beetles, while the centipedes eat both animals. An eyeless pseudoscorpion waves its threatening, glossy pinchers as we approach, triggered perhaps by some invisible remnant cornea reacting to our headlamps. We belly-down and push through a narrow, bumpy tunnel, eyes sweeping the walls and roof for twitching antennae or sudden scurries, until we emerge into a smaller chamber. Damp mud surrounds a dark pool of water so still it seems to have set like gelatin, and tree roots inquire into pockets of earth along the side walls. We switch off our lights, and pull the darkness into our lungs with every breath. Here in this world of Stygian blackness, eyes do no good, and the other senses take over. I can hear blood swooshing through my veins, and the creaks and squeals that accompany each slight movement echo against the silence. The organisms that live here, collectively known as “troglobites,” have totally committed to subterranean life.
They often have a reduced number of eyes and longer appendages and antennae, which act like supersensitive blind men’s canes. Here, the sun never shines, and most creatures have lost the UV-protective pigmentation that colors surface animals. The cool temperature is steady year-round, and the humidity is high and constant. The fragile organisms that have adapted to this stable world can survive nowhere else. At the hub of their food web are the springtails, primitive, wingless insects found in nearly every environment, from the dry valleys of Antarctica to the scorching deserts of the American Southwest.However, this cave is not completely isolated from the outside world. Leafhopper juveniles, aphid-like insects the size of a pencil eraser, have followed the tree roots into the cave to suck sap and molt into adulthood. They seem to be fully capable of completing their life cycle here, despite having no adaptations for living inside the earth. During the wet season, rainwater percolates down from the surface and swells the puddle to fill most of this cavern. This subterranean pond is the humidifying pan that keeps the cave comfortable. We turn on our headlamps and dip teaspoons into the little pool, finding endemic amphipods and isopods. These minute, translucent crustaceans lie dormant for most of the year, springing to life when the waters rise. They feed on mud and sludge at the pond’s bottom and make up the base of the aquatic food chain, which in caves east of the Rockies may include such distinctive creatures as blind crayfish and blind salamanders. Finally, we come to the last stretch. We push through a narrow horizontal slit, moving steeply uphill, with megatons of rock hanging overhead. I peer into a pit on the other side and find myself staring at a small dinosaur, an oversized curly-tailed scorpion, and a pair of lovers hand-in-hand. Somebody, obeying some primeval instinct also felt by the artists of Lascaux, has created a small tableau of clay figurines. The sculptor must have made several trips from the previous chamber, carrying silken clay to model the figures by torchlight, lovingly arranging them in a small natural scoop in the rock. It’s a celebration of life. Suzanne Ubick is Editorial Assistant of California Wild.
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