Nevada Cave Biology

Nevada's caves are homes to a variety of animals including bats, woodrats, and a variety of invertebrates, including some that are endemic to specific mountain ranges in Nevada.

Twenty-three bat species make their home in Nevada. Many of these spend part of their time in caves. One of the biggest concentrations is at Rose Guano Cave in east-central Nevada. One to three million bats use this cave as a migratory stop from about July to September each year. Mexican free-tailed bats make up the largest concentrations. The Nevada Department of Wildlife (NDOW) conducted a multi-year tagging of bats in that cave to learn more about the migration route. Numerous caves in Nevada have seasonal closures to protect bat populations.

If you visit a cave in Nevada, you are likely to find a midden. This is a nest made of sticks, dirt, and whatever debris a woodrat has brought to it. The woodrats urinate on the midden, making it stick together. These middens are passed down from generation to generation, and some are found in the Great Basin that are thousands of years old and very useful for climate studies.

Two woodrats live in Nevada, bushy-tailed woodrat (Neotoma cinerea) and desert woodrat (Neotoma lepida). The bushy-tailed woodrat's habitat is in caves and rocky areas from pinyon-juniper to alpine areas. The desert woodrat's habitat is rocky outcrops and cliffs from arid shrublands to pinyon-juniper. Both of these species appear to be declining (Rickart et al. 2008).

The primary studies on cave invertebrates have been conducted at Great Basin National Park (Krejca and Taylor 2003, Taylor et al. 2008) and Forest Service Caves in the Schell and Snake Ranges in eastern Nevada (Gilleland 2012). These studies have encountered several millipede species that have been described as new species. Cave pseudoscorpions also appear to differentiate between ranges. Mites, springtails, flies, and spiders appear diverse. Invertebrates are more commonly seen near cave entrances and in the twilight zone, where there are more nutrients.

A study looking at the wildlife use of cave entrances in pinyon-juniper and riparian habitats found over seventeen animal species use cave entrances. The most common, in order, are mice (Peromyscus sp.), cliff chipmunks (Tamias dorsalis), humans, woodrats (Neotoma lepida), and rock squirrels (Otospermophilus variegatus). The most common times for animal movement (which triggered a remote camera to take a photo) was between six p.m. and six a.m. (Baker 2015).

Other animals occasionally seen in Nevada caves include snakes, lizards, rabbits, birds, and even mountain lions.

Keep in mind that caves are homes for all these animals, and we are fortunate to get to visit them.

Millipedes are rather rare in the desert, as they generally like cool, moist habitats. Some species have taken shelter in caves and have been isolated for so long that they have evolved into different species on different mountain ranges. Millipedes are often identified by their gonopods (genitalia) under a microscope. Within the park we just know about two cave obligate millipedes, and fortunately they look substantially different. They are both detritivores, eating detritus (decomposing plant and animal parts and organic fecal matter).

The first cave millipede in the park was first collected in 2003 from Model Cave. It was later found in Lehman Cave--right on the edge of the trail! Amazing how it was not noticed for decades, but perhaps its extremely small size, less than 5 mm long, made it not-so-recognizable. The millipede was named Nevadesmus ophimontis, which is Latin for 'Nevada Snake Range.' A common name would thus be the "Snake Range millipede." One of the really cool things about this all-white millipede is that it is in its own new genus. That means it is substantially different from other cave millipedes (if they are somewhat similar, they are grouped with other species in the same genus and just get a new species name). For now, it is only known from a handful of caves in the South Snake Range. It is all white, having lost its pigment.

The second cave millipede in the park was first found in Water Trough Cave in 2006 and then in several of the wetter and higher elevation caves in the park. Dr. William Shear determined that it was a new species, Idagona lehmanensis, being part of the Idagona genus that is also found in Idaho and Utah and earning the species name in honor of Lehman Cave National Monument, the precursor to Great Basin National Park. Idagona lehmanensis is about 13 mm along (about three times as long as Nevadesmus ophimontis). Although it has only been found in caves in the South Snake Range, Dr. Shear thinks it hasn't been underground all that long, probably only since the latest Pleistocene climatic events forced it to find a cooler, moister habitat. It still has eyes (ocelli) and is often a yellowish or light tan color.

Pseudoscorpions are the top invertebrate predator in Lehman Cave. They are small arachnids, with eight legs. They prey on a variety of insects, including flies, beetles, larvae, and springtails (the bottom of the food pyramid in Lehman Cave).

The pseudoscorpions found in Lehman Cave have the scientific name Microcreagris grandis. They have a rather interesting history. The Lehman Cave National Monument Custodian (similar to today's superintendent) T.O. Thatcher noted and collected the pseudoscorpion in the 1930s. However, it took until the 1960s for it to be identified, when Dr. William Muchmore determined it was a new species and named it. Since then, this species has been found in other caves in the park, including alpine caves. However, it has not been found in caves on other mountain ranges, including the North Snake Range, where the Forest Service just completed an extensive bioinventory of its caves.

The pseudoscorpions in Lehman Cave are about 1/2 inch long, dark red, with little pincers. The females are lighter in color than the males. Since they have an exoskeleton, they molt as they grow, leaving behind the old shell. They may molt up to a dozen times during their lifetime.