What characteristic action do Green June Beetle grubs take when on the surface?

Green June Beetle grubs exhibit a unique behavior when found on the surface; they often crawl on their backs. This distinctive characteristic allows them to move in a way that may help them evade predators or navigate their environment more effectively. Being on their backs might also suggest an adaptation for survival, as this position could serve to protect their softer, more vulnerable undersides.

In contrast, behaviors such as digging into the soil, jumping vertically, or remaining stationary do not align with the observed actions of these grubs. They are not known for digging as a primary method of movement, nor do they employ a jumping action, which is atypical for this species. Remaining stationary is also not characteristic of their behavior, as interaction with their environment is crucial for feeding and survival. Thus, crawling on their backs is the most accurate depiction of their surface activity.