The most common and most likely answer to this crossword clue is the 6 plus 4 plus 5 letter word BERTHA ARMY WORMS
B
E
R
T
H
A
A
R
M
Y
W
O
R
M
S
Buddy explains!
The straight part
We know that "Voracious herbivores" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case voracious herbivores = bertha army worms.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.