What bad things do ladybugs do?

That they cluster inside people's houses and that they leave stains when frightened or stressed are the main negatives about ladybugs [Coccinellidae family]. Ladybugs just are looking for comfortable shelter from the icy, snowy, windy winter cold when they come inside. Inside, they often keep on doing what they do all summerlong: eat pests. Specifically, outdoors, it tends to be aphids, mites and scale. Indoors, it tends to be such mites as dust mites.

But it's still a bit of a shock to find ladybugs in such massive numbers behind window fixtures, drapes and blinds. When they're frightened or stressed, they react with 'reflex bleeding' that leaves a difficult to remove stain.