2020 USA Cave Animal of the Year
Welcome to the USA Cave Animal of the Year for 2020!
Our goal is to feature a different cave animal each year to increase awareness of the amazing creatures that live underground. This program started in Germany in 2009. In 2020, there will be programs in the USA, Australia, Germany, Italy, and Switzerland for the first time, as the effort expands for people to take note of these interesting and often overlooked organisms.
Why the fuss about cave animals?
People marvel at the beauty of caves, but many people don’t think about those caves being home to an amazing diversity of animals! Some of these animals have interesting adaptations to live in a world of complete darkness and often very low food resources. Worldwide, there are many species of animals that live in caves. Cave Animal of the Year seeks to increase awareness of these fascinating animals and the importance of caves as their homes.
Figure 1. The Great Basin Cave Pseudoscorpion (Microcreagris grandis), with the large red pedipalps obvious.
Meet our USA Cave Animal of the Year 2020
The USA Cave Animal of the Year for 2020 is the Great Basin Cave Pseudoscorpion (Microcreagris grandis Muchmore). It is a small arachnid in the family Neobisiidae and in the genus Microcreagris, which has over 20 other pseudoscorpion species.
Getting to know pseudoscorpions
Pseudoscorpions are small arachnids and are distant relatives of spiders, scorpions, harvestmen, and mites. They resemble scorpions but lack the stinging tail. Consequently, pseudoscorpions are sometimes referred to as false scorpions or book scorpions. Most species are very small, up to three-tenths (8 mm) in length and possess eight legs and large claw-like appendages called pedipalps that they use to grab prey. They eat variety of insects, including flies, beetle, larvae, and tiny springtails. There are almost 30 families of pseudoscorpions with more than 3,500 species found throughout the world. Some live above ground, but many live in caves. Some are endemic (found only in that location), indicating they may have been isolated or adapted to very specific living conditions.
More about the Great Basin Cave Pseudoscorpion
Pseudoscorpions are the top invertebrate predator in Lehman Cave, located in Great Basin National Park in Nevada. Great Basin cave pseudoscorpions have a rather interesting history. The Lehman Caves National Monument Custodian (similar to today’s superintendent) T.O. Thatcher noted and collected the first specimens in the 1930s. However, it took until the 1960s for the pseudoscorpions from the cave to be identified, when Dr. William Muchmore determined it was a new species and formally 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.
How do pseudoscorpions grow?
Baby pseudoscorpions (called protonymphs) emerge from a brood sac that is attached to the underside of the mother pseudoscorpion. The protonymphs then grow larger, going through several stages, called deutonymph, tritonymph, and finally adult. As they grow larger, the pseudoscorpions molt, or break open their exoskeleton, climb out, and grow another exoskeleton.
How do pseudoscorpions eat?
The Great Basin cave pseudoscorpion and other pseudoscorpions capture prey in their pedipalps, the claw-like appendages in front of their legs. These pedipalps are rather long and scissor-like, with spiny teeth to catch to hold their prey. The tips of the pedipalps have specialized teeth, through which the pseudoscorpion injects venom into its prey. They then use their chelicerae, which are smaller, muscular appendages, to help guide the prey to their mouth. They then regurgitate digestive enzymes into the prey, which dissolves the prey’s tissues, then slurp those up. Pseudoscorpions are not dangerous to humans; their prey consists of small insects and mites.
Pseudoscorpions are very different from scorpions
“Pseudo” means false, so “pseudoscorpion” means false scorpion. Pseudoscorpions are in an entirely different order than scorpions. Pseudoscorpions do not have a stinger like scorpions. They do have venom, but it is only dangerous to their prey, which are generally the size of house flies or smaller.
How to see a pseudoscorpion
Pseudoscorpions are often hiding under rocks near leaf litter and other debris that insects and mites might be feeding on. They are quite small and can be difficult to see to the untrained eye. On some cave tours, like though Lehman Caves, guides may show you a preserved pseudoscorpion.
With many pseudoscorpions found in just one area, it is important to try to disturb them as little as possible. Throwing trash into a sinkhole, letting contaminated water wash into a karst area (limestones and other soluble rock terrain that contain caves), or spraying graffiti in a cave could allow toxic chemicals into a cave system that could devastate these creatures. Although they may be small to our eyes, they are huge in the cave ecosystem. Toppling an apex predator could have many consequences on the rest of the life in a cave.
Subterranean ecosystems are often divided into major ecological zones that differ in abiotic factors, such as light, temperature, and humidity. These factors influence the types and numbers of organisms that occur in a given ecological zone. Caves are the most well-known examples of subterranean habitats. Caves can be divided into three major ecological zones.
The entrance zone marks the boundary between the surface and subterranean habitats and usually contains more species as well as greater variation in abiotic conditions, particularly temperature and humidity, compared to other zones. This zone is confined to the immediate area around cave entrances where light penetrates. Many species of plants and animals can be found in the entrance zone.
The transition zone (also called the twilight zone), marks the transition from the surface to subterranean habitats and connects the surface-dominated entrance zone with the dark zone. The transition zone is characterized by decreasing levels of light and habitats that are influenced by surface environmental conditions to a lesser extent than the entrance zone. Few plants grow in the transition zone, but many species of animals can exist.
Finally, the dark zone is the section of cave that lacks light completely and where environmental conditions are the most buffered from surface variability (i.e., conditions are usually the most stable). This deep cave environment is characterized by perpetual darkness, nearly constant temperature, and high humidity that is near saturation. No plant growth persists in the dark zone, and animals that exist here represent species that are most cave-adapted.
Subterranean habitats also can be divided vertically into distinct regions based on depth from surface and saturation with water. Each of these zones may host distinct communities of organisms.
Nearest the surface is the epikarst zone, which typically consists of networks of flooded or partially flooded cracks and crevices in bedrock and exists between surface and lower layers of unweathered soluble bedrock. Epikarst communities are dominated by small aquatic crustaceans, such as copepods and amphipods, but can also include terrestrial species. Water percolates through the epikarst and eventually reaches the vadose zone that contains a cave stream. A cave stream may be entirely fed by water from the epikarst zone or may also be fed by a sinking surface stream.
The vadose zone is the unsaturated area between the epikarst zone above and the water table below. The vadose zone of a cave is the area that can be explored by non-diving cavers (that is, you don’t need SCUBA gear!).
Finally, the phreatic zone is the region of a cave system that is permanently saturated with water and often contains large cavities. Wells in karst areas often access groundwater within this zone. Ultimately water within cave systems emerges back onto the surface at springs or seeps.
The ecosystem underground has some important difference from an above-ground ecosystem. Light is generally very limited and often absent. Nutrients may be very limited, unless there is a stream running through the cave or lots of cave organisms, like bats, who deposit guano in the cave. Generally, cave ecosystems are seen as being simpler versions of above-ground ecosystems. There is still a lot to learn.
Adapting to Life in the Cave
Many different organisms can be found in caves and other subterranean habitats. Some are accidentally in caves, having wandered in, or fallen into a pit. These species are not adapted to living underground and will perish if they cannot find their way back to the surface. However, other species purposefully live in caves for some or all of their lives. These creatures must adapt to an environment that is dark, generally has stable temperature and high humidity, and often has low food and nutrient resources.
Some species visit caves only occasionally. They are considered temporary or transient visitors, or trogloxenes, that use caves for shelter, to raise young, or to hibernate. Although caves are important to trogloxenes, they cannot live their entire lives underground and must return to the surface at some point during their lives. Examples of trogloxenes include cave-roosting bats and cave crickets.
Other organisms are more permanent residents of caves and subterranean habitats. Some may be found only in the entrance or twilight zones. These organisms called troglophiles can complete their entire life cycles within caves but often do not exhibit morphological adaptations associated with life in total darkness. Troglophiles also can be found in many habitats on the surface. Some species of salamanders, spiders, and flies are good examples of troglophiles.
Finally, some organisms, troglobites and stygobites, spend their entire lives in the dark zone of caves and other subterranean habitats. Many but not all of these species have evolved a suite of traits, termed troglomorphy, associated with life in the perpetual darkness of caves. These traits include loss or degeneration of eyes and pigmentation, elongation of appendages, and increased capabilities of non-visual senses, particularly touch, taste, and smell. Obligate cave species also tend to have slower metabolic rates and longer lifespans compared to their surface-dwelling relatives. Obligate cave species are broadly categorized according to habitat—terrestrial species are called troglobites (or troglobionts), while aquatic species are called stygobites (or stygobionts).
Figure 2. A Great Basin Cave Pseudoscorpion (Microcreagris grandis) eating a fly.
Figure 3. Another Great Basin Cave Pseudoscorpion (Microcreagris grandis) eating a fly.
Figure 4. Visitors looking at a preserved Great Basin Cave Pseudoscorpion during a National Park Service cave tour in Great Basin National Park
References and more information.
Cave Animal of the Year Programs
Inspired by the Cave Animal of the Year Australia. Cave Animal of the Year started with the German Speleological Federation (Verband der deutschen Höhlen-und Karstforscher e.V.)–hoehlentier.de