to think recruiters are snakes

[StarsInHerEyes3]

I have reason to believe recruiters are telling my employer when a current employee is jobhunting and sent their CV. My boss always seems to know when someone wants to leave and this must be how. He works with all the main recruiters in the area, and finds most new hires through recruitment agencies. I think the recruiters are giving him a heads up about fleeing employees to gain kudos.

Is this legal?

If they are putting their CV up online, your boss may just get an email when certain keywords are contained in a CV. If they are getting it from recruitment agencies, the recruiter would be unlikely to say directly that "Bob from accounts" is looking to leave however they would send a few CVs of someone that can fill his job so when he does hand his notice in, the boss will panic and think "I know who has candidates who can replace Bob". In theory anyway.

Quite possibly. Speaking from experience.