The idiom "蠢蠢欲动" (chǔn chǔn yù dònɡ) means "enemies or evildoers are busy preparing for destructive activities".
成语"蠢蠢欲动"（chǔn chǔn yù dònɡ）是指敌人或坏人准备进行活动。
The reduplication "蠢蠢" is used as an adjective. It originally referred to wriggling worms, now it implies all kinds of enemies or evildoers.
"欲动" means "be about to move" literally, and "in preparation for an attack or sabotage" generally.
In modern Chinese, "蠢蠢欲动" means "be ready to make troubles", so it is derogatory. However, it is often used wrongly even by Chinese people. For example, there is a sentence in Information Times (a Chinese newspaper) on Sep. 9, 2010, "教师节马上就要到了，学生和家长都蠢蠢欲动，准备礼物", which meant that "students and parents are busy preparing gifts for teachers as the Teachers' Day is approaching". Correctly, we can say "人多的街头，窃贼蠢蠢欲动", which means "thieves are ready to take actions in the crowded street".
An idiom has been inherited together with its conventionalized emotional color, which cannot be changed to cause misunderstanding. So, just keep this in mind!