Ladybugs eat soft bodied bugs.
http://www.ladybuglady.com
Ladybugs eat Aphids. Aphids are soft bodied insects that suck the juices out of plants. If you have roses in your garden, you have seen aphids. Aphids also come in a variety of colors and not all ladybugs like all the "flavors" of aphids. Ladybugs will also feed on scale insects and plant mites.
Lady bugs will eat young mites and larva. Like predatory mites they will not eat all mites.
That's what I've always thought (that ladybugs mostly eat aphids). Didn't know they eat some 'plant mites'. Wish she'd added some specificity regarding 'plant mites'. Only mites I've ever been fearful of are spider mites.
I used some ladybugs once. They flew right into the lights and died.
That was my experience also. Not all of them, but most.