Trogloxenes are populations or species that are found in caves but cannot complete their life cycle there. These are sometimes divided into two subgroups, the cave visitors (subtroglophiles) and the accidental visitors (eutrogloxenes). A cave visitor is an animal that spends specific periods of its life in a cave (overnight stay, hibernation, hiding place, etc.). An accidental or errant visitor is an animal that occasionally enters caves but has its actual habitat above ground. The term is also used for animals that are regularly found in caves, but are dependent on leaving the cave at least at one stage of their lives.
The term trogloxen is made up of the Greek words trogle "cave, hole" and xeno "alien", meaning "cave alien". This is probably a bit of a misnomer, because these animals are not alien, but are in fact sometimes found very frequently and/or in large numbers in caves. The name is intended to express the fact that they are not adapted to this habitat. This is why the two terms guests and visitors fit much better. However, a distinction can be made between two types of such guests. Those who come again and again on purpose because the caves offer an advantage, are called cave visitors (subtroglophiles). And those who enter the cave more or less by chance and take no advantage of it, but leave the cave again unscathed, are called accidental visitors (eutrogloxenes).
However, this is also where the problem begins, which results from the fact that the three-part division of cave animals presented here is so simplified that it was no longer sufficient in the 19th century. As a result, several alternative categorizations were presented over the 20th century, none of which really caught on. One major problem is that different systems lead to different definitions of names and confusion of terms. This division of the trogloxenes into two classes is a kind of compromise, which effectively raises this traditional division to four classes, but at the same time retains the names. In addition, the class of subtroglophiles is sometimes assigned to the trogloxenes, sometimes to the troglophiles, and there are good reasons for both approaches.
Among the trogloxenes, there are animals which enter a cave by mistake are unable to cope with the habitat. They are unable to orientate themselves in the dark, have no means of survival, but also cannot find their way out again, so they die in the cave. Some authors categorize these as accidental guests, as eutrogloxenes, we prefer to say they are not cave animals at all, they are epigean.
And there is another subgroup, animals whose bones were brought into the caves by humans, hyenas or floods. However, there is no evidence that they actually lived in caves. For example, the cave goat (Myotragus balearicus) and the cave lion (Pantera leo spelaea) were originally described as cave animals, but are probably not. They are not even accidental visitors.
But it is in this group, the trogloxenes, that most of the animals that normal people associate with cave animals can be found. Bats, cave bears and swallows are the cave animals well known from literature and pop culture. There are also various toads, newts, salamanders, rodents such as mice or dormice, bears, woodlice, weaver gnats, beetles, snails, birds and even a species of snake. In fact, they belong to the subtroglophiles, so in a way they are "between" the trogloxenes and troglophiles. This is where the difference between the various definitions of the terms becomes particularly unpleasant. For example, there are bats that like to use caves as roosts and for hibernation, but can also cope with rock crevices, hollow trees or human ruins. And yet they have an adaptation, the echolocation, with which they can navigate in the dark cave, just like the guacharo or oilbird (Steatornis caripensis), a bird that also has an echolocation system. However, as they are nocturnal, it can also be argued that this is also helpful when hunting on the surface. According to one definition, they should belong to the troglophiles because of their adaptation with the echolocation system. According to another definition, they must be counted among the trogloxenes because they have to leave the cave to hunt.