A wolf and a jackal（豺，走狗） often went hunting together. Once they came to a sheepfold（羊圈） the walls of which were frimly built and too high for them to get over. Then they had an idea: Since the wolf had long forelegs and short hindlegs, while the jackal had short forelegs and long hindlegs, the wolf stood on the necks of the jackal, and the jackal stood up on its hindlegs. In this way the wolf climbed over the wall to where the sheep were.

This idiom is used to describe doing evil¹ things in collusion with others.

解释】： 狼和狈一同出外伤害牲畜，狼用前腿，狈用后腿，既跑得快，又能爬高。比喻互相勾结干坏事。

成语故事】：传说古时候，有狼和狈两种野兽。狼的前肢长，后腿短；狈的前肢短，后腿长。有一次，狼和狈一道去偷羊，但羊圈又高又结实，既跳不进，也撞不开。于是它们就想出了一个办法：狼骑到狈的脖子上，狈用两条后腿站起来，把狼拖得很高，然后狼就用它的两条前肢攀上羊圈，把羊拖走。根据狼和狈勾结干坏事的传说，人们创造了成语狼狈为奸。

狼狈为奸比喻坏人互相勾结做坏事。