The most common and most likely answer to this crossword clue is the 11 letter word TROGLODYTES
I've seen this crossword clue in The Daily Telegraph
T
R
O
G
L
O
D
Y
T
E
S
Buddy explains!
The straight part
We know that "they shelter in caves" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they shelter in caves = troglodytes.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TROGLODYTES mean?
TROGLODYTES noun- A member of a supposed prehistoric race that lived in caves or holes, a caveman.
- (by extension) Anything that lives underground.
- A reclusive, reactionary or out-of-date person, especially if brutish.
- The Eurasian wren, Troglodytes troglodytes.
- A person who chooses not to keep up-to-date with the latest software and hardware.