As we all know, all things grow with the help of the sun. So, in the lightless underground, could we still find the thriving scene of life as in a primeval forest? The answer is definite: No. The deeper you go into a cave, the simpler and more primitive the food chain becomes. Therefore, it’s absolutely impossible to encounter creatures like aliens or giant pythons (excluding human-made ones). Caves are filled with huge rocks and soil—what would such large creatures eat if they lived there long-term? With this concept in mind, let’s talk about what kinds of organisms actually live in caves...
According to ecological characteristics, cave-dwelling animals can be divided into the following three categories:
True cave animals:These species exist only in dark environments and cannot survive outside caves. They typically lack pigmentation, have degenerated or absent visual organs, and possess slow metabolisms. Examples include cave blind fish, cave salamanders, cave crickets, cave centipedes, and cave tadpoles.
Troglophiles (cave-loving animals):These animals complete their life cycles in caves but can also survive in dark environments outside caves. Examples include cave rats, earthworms, and certain types of salamanders.
Trogloxenes (cave guests):Animals that temporarily inhabit caves, such as bats, swifts, snakes, and some insects.
In recent reports and explorations, many more animals have been discovered. In the mysterious underground world, who knows how many unknown creatures are waiting to be found and understood?
The above animals outline a basic food chain:
In water, cave tadpoles feed on microorganisms, cave blind fish eat the tadpoles, and bats prey on the blind fish. Microorganisms, in turn, decompose bat droppings and the bodies of blind fish.
On land, cave crickets and cave centipedes live off the feces of mice or bats, while the mice or bats may prey on the crickets and centipedes. Their corpses and waste are then broken down by microorganisms.
Caves have their own climatic phenomena, mainly regulated by flowing water and convective air. The interior of a cave is actually a relatively constant-temperature environment. Elevation has some influence on the average temperature inside a cave, but it generally ranges between 11–15°C. This explains why caves are said to be “warm in winter and cool in summer.”
Airflow within a cave not only regulates climate but also greatly affects the growth of stalactites. Therefore, when exploring or developing caves, avoid carelessly breaking through passages—such actions often lead to devastating destruction.
People entering caves often feel a sudden strong gust of wind when passing through narrow passages, but once they’re through, everything goes calm again. This brings us to the “chimney effect,” which is caused by differences in height between cave entrances (or fissures), resulting in the natural convection of air with varying temperatures inside and outside the cave. The chimney effect shows strong seasonal changes—during winter, hot air inside the cave moves upward, while in summer, the direction reverses. In spring and autumn, when cave and outside pressures are similar, the daily temperature variation causes shifting wind directions at different times of the day.
The flow of underground rivers can also generate air movement, a phenomenon known as the “riding effect.”
Having covered these points, we can now address a common concern: Is there any toxic gas in caves? Is there enough oxygen?
What you should truly be concerned about is the sufficiency of oxygen. Let’s look at some data: the average CO₂ level in the atmosphere is 0.03%. Environments with CO₂ levels of 3% or higher pose dangers, with specific symptoms including rapid breathing, increased pulse, headache, dizziness, tinnitus, and flickering candle or match flames. Because CO₂ is 1.53 times denser than air, it often settles at the bottom of caves. That said, not all cave floors have high CO₂ levels. Based on my experience, if a cave passage suddenly feels warmer or you detect an unusual smell, it likely means the passage is blocked or poorly ventilated—so you should be cautious. Cool, well-ventilated, and water-flowing passages are usually very safe.
Caves contain high levels of negative ions, which can stimulate the self-cleansing function of the human respiratory system and enhance immunity—this is also why people often feel energized upon entering a cave.
Caves may also contain trace amounts of radioactive elements. Pure carbonate rocks have lower radioactivity compared to other rock types. However, for those working or staying in caves long-term, cumulative exposure time should still be monitored. This is also why developed caves undergo regular radiation monitoring.