Validation of eDNA methods for managing the terrestrial invasive snake Lampropeltis californiae on the Canary Islands

Invasive snakes are among the most challenging invaders worldwide due to their exceptionally low detection rate and grave ecological impacts. Environmental DNA (eDNA) has emerged as a promising tool to improve invasive snake detection and enhancing management programs, yet its application to terrestrial snakes remains underexplored. This study provides the first advances in the use of eDNA techniques to detect the terrestrial invasive California kingsnake (Lampropeltis californiae). We designed L. californiae-specific primers and tested their effectiveness in detecting the species in different environmental samples, including swab samples from underneath artificial cover objects (ACOs) made of different materials, soil beneath ACOs, randomly collected soil, and researchers' boots. Additionally, we conducted a controlled experiment to assess the accumulation and degradation rate of L. californiae eDNA over a 14-day period (7 with snakes in the terraria and 7 after having removed them). We detected L. californiae eDNA in 9.31% of swab samples, in 2.22% of soil samples under ACOs, and in 2.56% of boot samples, while no detections appeared in randomly collected soil or controls. In the controlled experiment, eDNA was undetectable in terraria prior snake introductions, but remained detectable throughout the study, with no evidence of snake eDNA degradation after snake removal. These findings provide key insights for the implementation of an eDNA-based protocol for the detection of L. californiae in Gran Canaria, offering a valuable tool for monitoring this invasive species. Furthermore, this study could be used for refining eDNA methodologies to detect other elusive terrestrial snake species elsewhere.