Because of this tradeoff, these plants enjoy a competitive advantage in the barrens that they lack elsewhere The rough green snake, and nine species of moths and butterflies that are rare in the state of Pennsylvania, including the cobweb skipper, the barrens blackmoth, and the mottled duskywing make their homes in the serpentine barrens. Southeastern Pennsylvania includes a significant part of the State Line Serpentine Barrens, which is the largest occurrence of serpentine barrens habitat in the eastern United States. The state line barrens consists of seven sites totaling about 850 hectares in area. The sites are situated along 20 km of the Mason-Dixon line and located in Chester and Lancaster counties of Pennsylvania and Cecel County of Maryland. Six of the seven sites are entirely or mostly in Pennsylvania.
Serpentine barrens are rare and provide habitat for many rare and endangered species.
These areas, however, are currently being threatened by human behavior. Mining and quarrying have destroyed much of the barrens. Particularly in southeastern Pennsylvania, development spurred by suburban sprawl has led to the conversion and consumption of much barrens habitat. Human presence in and around the barrens affects its wellbeing in another important way. Because it is perceived as a threat, humans often actively suppress the natural fires that are so crucial to barrens life.