What do bugs do for plants?

Help them grow or perish is what bugs do for plants.

Specifically, a bug can be defined as an insect with piercing, sucking mouthparts. Examples include such potential insect pests as aphids, cicadas, leaf- and plant-hoppers, and shield bugs. An infestation of bugs is prefatory to plants getting damaged or diseased to the extent that they grow improperly or even perish. As part of Mother Nature's food web, they may be viewed in limited numbers and under controlled circumstances as keeping such beneficial arthropods as ladybugs alive and as "weeding" out plants that are less equipped to endure or survive environmental stresses.