The mysterious world of biofluorescence in terrestrial ecosystems is mesmerizing. Though not as ubiquitous as in the ocean, it is not a rare phenomenon on land. Fluorescence occurs in all major phyla of terrestrial animals (Platyhelminthes, Mollusca, Annelida, Nematoda, Onychophora, Arthropoda, and Chordata) and their subgroups, with diverse fluorophores and performance. In this chapter, we make a general review on the fluorescence in terrestrial animals first, including their systematic distribution, research history, fluorophores, and proposed functions for each group among several other aspects. A systematic observation on the fluorescence of fireflies is reported for the first time. The co-occurrence of biofluorescence and bioluminescence in luminescent land snails, earthworms, potworms, millipedes, and fireflies is a fascinating issue. Though the biochemical mechanism of photogenesis is not fully understood in many terrestrial animals except fireflies, it appears that biofluorescence and bioluminescence do not have clear interaction during the light production process. However, fluorophores and luminophores are usually biochemically related and are different from the photogenic mechanism of jellyfish and several marine creatures whose ultimate light emission is made through energy transfer from bioluminescence to biofluorescence by green fluorescent protein (GFP) or its variants. The role of fluorescence is disputative. In general, nocturnal animals or animals having cryptic living styles, e.g., in earth or under shelters like tree bark or rocks, tend to exhibit UV fluorescence more frequently than animals that are diurnal or inhabit open environments. This pattern is evident in fireflies wherein only nocturnal and luminescent species exhibit noticeable UV fluorescence (likely from luciferin), which is dim or absent in diurnal or crepuscular fireflies. It is unlikely that occasionally induced UV fluorescence in natural environments can play a significant role in intra- or interspecific communication in fireflies or other nocturnal animals.
Part of the book: Bioluminescence