The most common and most likely answer to this crossword clue is the 7 letter word HYDATID
I've seen this crossword clue in The Guardian
H
Y
D
A
T
I
D
Buddy explains!
The straight part
We know that "tapeworm larva" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tapeworm larva = hydatid.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 HYDATID mean?
HYDATID noun- A cyst due to infection by larvae of some species of the tapeworm Echinococcus.