O. vernalis is hunted by various predators, including the
red-tailed hawk,
great blue heron,
rough-legged buzzard,
bears,
raccoons,
foxes, and the common house
cat. Humans also find this snake in the wild and keep it for a pet. It is subjected to commercial collection because of its attractive skin coloration, passive nature, and small size. However, this snake is not known to survive well in captivity. Because its populations are usually isolated and small in size, this commercial collection can greatly affect the overall population. Pesticides are particularly harmful to the snake when used in riparian areas, mountain foothills and meadows. Because the smooth green snake's diet consists mainly of insects, insecticides put the snake at great risk in areas where they are applied. The reduction of its prey is a major cause of the death of the snakes, as well as one of the most important natural threats to its population. Habitat destruction is caused by road building, logging, cattle grazing, and the draining of streams. Logging and mining conducted in a smooth green snake habitat can be a source of snake mortality. Roads and highways are a major cause of deaths, especially those near streams or other habitats the snake occupies. Livestock grazing has been found to reduce snake populations in some areas, where five times the amount of snakes were found on ungrazed areas, compared to grazed areas. The effects of livestock grazing include the reduction of grass, changes in tree species, compaction of soil, and more erosion, which affect the reptile population in these areas. Flooding, freezing, and destruction of dens can destroy large numbers of smooth green snakes, as well as other species of snake with which it may hibernate. Human recreational activities, such as off-road vehicles near wetlands, are also damaging its habitat. Lakes and streams are enjoyable areas for recreation, but human activity in these areas can degrade them. The use of off-road vehicles in or around wetlands, however, is the most damaging recreational activity.
Mud bogging significantly damages and destroys these areas. Also, oil and gasoline from off-road vehicles has been found in snake habitats. ==Conservation status==