Use of fluorescent powder as a method for marking millipedes

Abstract

Millipedes (class Diplopoda) are a diverse group of detritivores that are crucial for nutrient cycling and decomposition. Despite this, there are gaps in our knowledge of their ecology, such as home range, movement patterns, population size, and sociality. This is partly due to the fact that there has been no effective method for marking millipedes, because of their small size, elongate shape, and fossorial behavior. There has been previous research on the usage of fluorescent powder for mark-recapture and movement studies on insects. We tested the effectiveness of fluorescent powder as a marking method using members of the North American families Parajulidae (Julida) and Xystodesmidae (Polydesmida). Initial lab studies assessed the longevity of fluorescent powder and impact on mortality using twenty individuals: ten marked with powder and ten unmarked. For both species, the use of fluorescent powder had no apparent impact on individual mortality. Areas on the millipede where powder was retained varied, with Ptyoiulus impressus (Say, 1821) retaining powder on the sterna and Dicellarius paynei (Shelley, 2002) retaining powder under the paranota. Immediately after the mortality study, the powder was assessed for longevity when exposed to water, by submerging each remaining marked individual into water, then assessing changes in the markings. Exposure to water had no apparent impact on the fluorescent powder markings. A field experiment was conducted to assess longevity in natural conditions, possible transfer between individuals, and survival of marked individuals in the wild. Marked and unmarked individuals were placed into mesocosms for approximately two weeks. All marked individuals retained markings and were easily differentiated from unmarked individuals. Overall, fluorescent powder shows promise as an effective method for marking individual millipedes, even in field conditions, and could prove useful for future studies.