The most common and most likely answer to this crossword clue is the 9 letter word PARASITES
I've seen this crossword clue in The Guardian
P
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More clues leading to the result PARASITES
Buddy explains!
The straight part
We know that "they need indulgent hosts" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they need indulgent hosts = parasites.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 PARASITES mean?
PARASITES noun- A person who lives on other people's efforts or expense and gives little or nothing back.
- A sycophant or hanger-on.
- An organism that lives on or in another organism of a different species, deriving benefit from living on or in that other organism, while not contributing towards that other organism sufficiently to cover the cost to that other organism.
- A climbing plant which is supported by a wall, trellis etc.
- A retainer or companion of an ancient Celtic warrior, who praised him in song or poetry at gatherings; a bard.