Open a can of worms
/ˈəʊpən ə kæn əv wɜːmz/informalUK · US
What does “Open a can of worms” mean?
Open a can of worms means to start dealing with something that creates further difficult problems
A simple question can open a can of worms. Asking who pays for one repair, for example, might uncover years of disagreement over shared costs.
The phrase often warns that a subject will be hard to manage. It does not mean the subject should never be discussed.
When do people say it?
Use it when a question, discovery or attempted fix brings up more complications than expected.
“Changing the shared driveway opened a can of worms about who owned the land.”
Is it formal or informal?
Register: informal. It is most at home in everyday conversation rather than formal writing. Most common in UK and US.
Where does it come from?
The image is of opening a container of worms and finding them difficult to keep under control.
Origin confidence: Disputed; treat with caution
How do you say “Open a can of worms” in other languages?
Related idioms
- The tip of the iceberg, A small visible part of a much bigger problem.
Last updated 2026-09-19