狼狈为奸

lang bei wei jian: In trying to catch a meal, the wolf haplessly kept running into the flock of sheep, scattering them and ending up hungry. The clever ferret, who was too small to catch a giant sheep but who was also starving, saw an opportunity. "Wolf! Let me help you!" said the ferret, climbing onto the wolf's back. The ferret steered his new friend slowly towards a slower, sickly sheep, then told the wolf exactly when to pounce--with great success! The two conspirators then enjoyed a feast together.

...just picked up this story in class, talking about symbiosis in different ecosystems. I clarified, saying symbiosis is a good thing for all parties in the ecosystem--whereas lang bei wei jian has a bit more negative connotation.