The most common and most likely answer to this crossword clue is the 3 letter word BOT
I've seen this crossword clue in The Guardian
B
O
T
More clues leading to the result BOT
Buddy explains!

The straight part
We know that "Maggot" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case maggot = bot.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 BOT mean?
BOT noun- The larva of a botfly, which infests the skin of various mammals, producing warbles, or the nasal passage of sheep, or the stomach of horses.
- To bugger
- To ask for and be given something with the direct intention of exploiting the thing’s usefulness, almost exclusively with cigarettes.
- A physical robot.
- A piece of software designed to complete a minor but repetitive task automatically or on command, especially when operating with the appearance of a (human) user profile or account.
- A computer-controlled character in a video game, especially a multiplayer one.
- To use a bot, or automated program.