Their habit of eating aphids and scale insects (and chasing the odd sprinkle) is considered to be of considerable benefit. They also require pollen which they obtain from mustard plants, buckwheat, coriander, red or crimson clover, carrot family plants and legumes.
As I was growing up, we liked to watch ladybugs in the summer and we didn't see them in the winter, (and yes, the light bulb had been invented by then.) They seek shelter, looking for warmth in woodpiles, sheds and houses, only to become active on sunny warm days or when we turn up the heat. So why are we seeing so many of them indoors now? Immigration, or rather importation may be part of the answer.
The Asian lady beetle, or Japanese ladybug (Harmonia axyridi) was imported to the US multiple times since 1918 to control aphids but really became established starting in 1988. It spread in the Midwest over the next 5 years while separate introductions in the Northeast and Northwest US hastened their spread.
There is no doubt that the Asian lady beetle is effective in helping to control aphids and scale insects. It also is controlling the native lady beetle populations by out-competing them and occasionally eating them. The long term consequences of this on our native species is not yet known.
"Many people now view this species as a nuisance, partly due to their tendency to overwinter indoors and the unpleasant odor and stain left by their bodily fluid when frightened or squashed, as well as their tendency to bite humans." (Wikipedia).So when does an introduced species cross the fuzzy line into an invasive species? That is usually in the eye of the beholder. I guess it depends on whether they are eating your aphids or your neck.