Ladybugs lay their eggs on various types of plants that are infested with aphids (photo on right). A ladybug can eat thousands of aphids during it's larva and adult stages.
The spiky, crawling larvae look nothing like the adult ladybug...except for the familiar black and orange color.
Aphids weaken, and can eventually kill plants. I found these aphids, and ladybug pupae on a Ninebark shrub (Physocarpus opulifolius 'Diabolo') and on Purple Leaf Sand Cherry (Prunus x cistena). I've also seen them recently on Dill seed heads.