Caves are naturally occurring hollows in the ground and are usually large enough for a person to enter. They are made by a process known as "speleogenesis"! It sounds complicated, but this basically describes how caves begin and develop. They're not just small areas we can walk around in either, caves can extend deep into the Earth's crust - the deepest explored cave is the Krubera cave in Georgia and measured 7,208ft from the entrance to the bottom! Wow!
Caves are found all over the world, but the most common ones found in the UK are solutional caves (made when groundwater seeps through limestone and chalk) and sea caves (made when waves continually hit weak cliffs, causing them to erode - meaning to wear away). A small area of the UK is made up of limestone rock, which means there are more caves there, but only a few are easy to reach so they are quite underexplored. The highest number of underwater caves are found in the Bahamas, with over 1,000 and counting!
Off the coast of Scotland is the uninhabited island of Staffa, and here are several sea caves - the largest is Fingal's Cave. This cave is over 200ft long!
Caves are important ecosystems for animals that live there, known as "troglobites" - these are animals that spend their entire lives in caves and have adapted to it. Most caves are surrounded by complete darkness, so many cave species have lost the ability of sight and nearly all troglophiles (animals that spend their lives in caves) have evolved to be pale in colour. Pigments that protect against the sun are useless in a cave! Examples of troglophiles include molluscs, worms, spiders, millipedes, centipedes, crustaceans, insects, fish, amphibians and reptiles.
No known mammals spend their entire lives just in caves; many bat species will spend daylight hours resting in caves but will leave to hunt at night - these are called "trogloxenes".
Caves have an important place in our history too. In the past they were used by our ancestors for rituals and were sometimes even used as burial grounds. Sea caves were also used as shelter when early modern humans started to first use the sea for food and other means.
In general, the largest threat to a cave system is from collapse or severe erosion (wearing away). Fortunately such events are rare!
Read about more fascinating habitats here!