a can of worms

can of worms

A situation that, once started, is likely to become problematic or have a negative outcome. Getting involved in the minor border conflict has become a can of worms for the country, with no end to the military engagement in sight. You can try reformatting your computer, but once you open that can of worms, you'll probably be working on it for days.
See also: can, of, Worms
Farlex Dictionary of Idioms.

a can of worms

COMMON A can of worms is a situation or subject that is very complicated, difficult or unpleasant to deal with or discuss. Now we have uncovered a can of worms in which there has not only been shameful abuse of power, but a failure of moral authority of the worst kind. Note: You can also use the expression to open a can of worms, meaning to start dealing with or discussing something so complicated, difficult or unpleasant that it would be better not to deal with or discuss it at all. Whenever a company connects its network to the Internet, it opens a can of worms in security terms. Many people worry that by uncovering the cause of their unhappiness they might be opening a can of worms that they can't then deal with.
See also: can, of, Worms
Collins COBUILD Idioms Dictionary, 3rd ed.

a can of ˈworms

(informal) if you open up a can of worms, you start doing something that will cause a lot of problems and be very difficult: I think if we start asking questions we’ll open up a whole new can of worms. Perhaps we should just accept the situation.
See also: can, of, Worms
Farlex Partner Idioms Dictionary
See also:
  • can of worms
  • can of worms, it's a/like opening a
  • get into a mess
  • addict
  • addict (one) to (something)
  • addict to
  • itchy fingers
  • get itchy fingers
  • get someone's back up
  • have back up
References in periodicals archive
Apartment block cheese, 47 chicken In fact, it is a can of worms - a huge, enormous, cheapo brand vat of things which look like worms but don't taste like them because these were on offer and look, we have 16 cans of worms because there was a special breasts, Flintstone slabs offer.
Very kind of him to offer to shop but don't put bunting out too quickly; Laura KEMP FAMILY MIS-FORTUNES
When I was little I always went to my grandmother's house to rummage through her compost pile and bring a can of worms home for my room, who accepted them gratefully and later dumped them in her flower garden.
The basics of vermiculture
A PET lover opened a can of worms when a tin of cat food exploded, showering her with maggots.
`Horror movie' in cat food can
SUE Crane really did open a can of worms when she fed her cats.
EXPLODING CAT FOOD SHOWERS WOMAN IN MAGGOTS!; Nine out of ten maggots prefer Whiskas