Exclude subdirectory in Grunt-contrib-copy

I'm copying some folders with grunt-contrib-copy. I'm trying to exclude a subdirectory in the root. I can prevent the contents of the _sprites folder from being copied, but inevitably the sprites copy is always copied. How do I prevent the folder from being copied? Here is what I have:

...
copy: {
    deploy: {
        cwd: "src/",
        expand: true,
        src: [
            "**/*",
            "!**/_sprites/**/*"
        ],
        dest: "deploy/"
    }
},
...

I've attempted !_sprites, !_sprites/ and others, but none appear to yield the results I want.