Quick answer: “A Can of Worms” means A complicated situation that causes even more problems when examined.
A can of worms — a complicated or sensitive situation that, once started or examined, creates even more problems or complications than expected.
Origin & History
The idiom comes from the literal image of opening a can of fishing bait — once the lid is off, the worms escape in all directions and are almost impossible to put back. The phrase entered common American usage in the mid-20th century, with early printed examples from the 1950s. It gained popularity through journalism and political commentary, where complex policy issues were frequently described as "cans of worms."
The idiom is widely used today in business, politics, and everyday life. It typically signals a warning: before proceeding, be aware that this issue is more complex than it appears, and opening it up may cause more difficulties than it solves. Learners who want to check other figurative expressions can consult general reference works such as the Cambridge Dictionary, which document how such idioms are used today.
Example Sentences
| Sentence | Context |
|---|---|
| "Asking about the budget will open a real can of worms — everyone has a different opinion." | Office politics |
| "The new policy opened a can of worms regarding employee contracts." | Workplace complexity |
| "I don't want to open that can of worms about who said what at the meeting." | Avoiding conflict |
| "Investigating the accounts turned out to be a can of worms — there were errors going back years." | Financial discovery |
| "Bringing up old arguments is just opening a can of worms that we'd rather keep closed." | Relationship advice |
| "The proposed merger is a can of worms — legal, financial, and cultural issues all at once." | Business strategy |
Use It in Conversation
Dialogue Example
Sarah: Should we review the terms of the partnership contract?
Daniel: Careful — that could be a real can of worms. There are clauses both sides disagree on.
Sarah: Fair point. Let's get legal advice before we raise it.
How to Use It
This idiom is informal to neutral. It is most commonly used with "open" (as a verb): "open a can of worms". It can also be used as a noun phrase: "this is a can of worms". It signals complexity and warns against hasty action.
Common Mistakes
Mistakes to Avoid
Let's open a can of worm before the meeting.
Let's open a can of worms. — Always use the plural "worms".
That situation was a can of worm.
That situation was a can of worms. — The idiom requires the plural form.
Similar Idioms
Practise This Idiom
Want to understand the grammar behind this? Explore our Grammar guides.
Quick Check: A Can of Worms
2 questions — test what you just learned.
1. What does “A Can of Worms” mean?
2. Complete the sentence: “"The new policy opened _____ regarding employee contracts."”
Frequently Asked Questions
What does "a can of worms" mean?
"A can of worms" describes a complicated or sensitive situation that creates even more problems once it is examined or started. Opening it makes things worse rather than better.
Where does "a can of worms" come from?
The phrase comes from the image of opening a tin of fishing bait — once the worms escape, they cannot be easily contained. It entered American English in the 1950s, particularly in journalism and political commentary.
Can you give an example of "a can of worms" in a sentence?
Example: "Asking about the budget will open a real can of worms — everyone has a different opinion." It warns that raising the issue will cause more problems.
Is "a can of worms" formal or informal?
The idiom is informal to neutral. It is suitable for conversation and semi-formal writing, including emails and articles, but should be avoided in formal reports.
What CEFR level is "a can of worms"?
Typically B2 (Upper-Intermediate). It is widely used in journalism, business, and everyday spoken English.
What verb is most commonly used with "can of worms"?
The most common verb is "open": "open a can of worms". This reinforces the image of removing the lid and releasing the problem.
What idioms are similar to "a can of worms"?
Similar expressions include "Pandora's box" (a source of unforeseen trouble), "hornets' nest" (a situation that causes anger and conflict), and "minefield" (a situation full of hidden dangers).
Can "a can of worms" be used positively?
Rarely. It almost always carries a negative or cautionary meaning, suggesting that the situation is more complex and problematic than it appears.
How do I practise "a can of worms"?
Write two sentences: one using "open a can of worms" as a warning, and one using "it's a can of worms" as a description. Then try LexFizz Flash Cards.
Is "a can of worms" used in British English?
Yes. The idiom is used in both British and American English with the same meaning, though it originated in American English and remains slightly more common there.