Glowworms: a review of Arachnocampa spp. and kin

Abstract

The term 'glowworm' is used in connection with the flightless females of lampyrid fireflies and to describe the luminescent larvae of certain fungus gnats that belong to the subfamilies Arachnocampinae, Keroplatinae and Macrocerinae of the dipteran family Keroplatidae. This review focuses on the luminescent larval fungus gnats. The weakly luminescent species of the Holarctic feed mainly on fungal spores, but some, such as Orfelia fultoni, have turned to a carnivorous diet. Larval Australian and New Zealand Arachnocampa spp. produce brighter in vivo (but not necessarily in vitro) lights, live in cool, damp and dark places and are exclusively predatory. They lure their prey (usually small flying insects) with the help of their blue-green light emissions towards snares consisting of vertical silk threads coated with sticky mucus droplets. Fungus gnats with similar 'fishing lines' are found in the Neotropics, but they are not luminescent. The larval stage is longest in the life cycle of Arachnocampa, lasting up to a year, depending on climatic conditions such as temperature and humidity as well as food supply. In A. luminosa, but not the Australian A. flava, female pupae and even female imagines are luminescent. However, it remains to be demonstrated whether it is the light of the female, a pheromone or both that attract the males. Light organs and the chemical reactions to produce light differ between the holarctic and the Australian/New Zealand species. Prey is attracted only by the glowworm's light; odours of the fishing lines or the glowworms themselves are not involved. Recognition of the prey by the glowworm involves mechano- and chemoreception. The eyes of both larval and adult glowworms are large and functional over a spectral range covering UV to green wavelengths. Adults are poor fliers, live only for a few days, have degenerate mouth parts and do not feed. Maintenance of glowworms in captivity is possible and the impact of tourism on glowworms in natural settings can be minimized through appropriate precautions.

Roles of biogenic amines in regulating bioluminescence in the Australian glowworm Arachnocampa flava

“…Both groups use bioluminescence to attract flying insects, which are ensnared in sticky silk and mucus traps constructed by the relatively immobile larvae (Fulton, 1941;Meyer-Rochow,segments of the four Malpighian tubules (Wheeler and Williams, 1915).…”

The Terrestrial Bioluminescent Animals of Japan

“…Larvae of all Arachnocampa species live and glow on the ceiling of caves or overhanging riverbanks, and are well known as "glowworms" for tourism. Pupae of A. luminosa were reported to be luminous, and the light intensity was stronger in females than in males (Richards, 1960;Meyer-Rochow, 2007). The Tama Zoological Park, Tokyo, Japan, has been successfully maintaining the Australian luminous keroplatid Arachnocampa richardsae since 1987 (Takaie, 1997;Meyer-Rochow, 2007; H. Takaie, personal communication).…”

“…Pupae of A. luminosa were reported to be luminous, and the light intensity was stronger in females than in males (Richards, 1960;Meyer-Rochow, 2007). The Tama Zoological Park, Tokyo, Japan, has been successfully maintaining the Australian luminous keroplatid Arachnocampa richardsae since 1987 (Takaie, 1997;Meyer-Rochow, 2007; H. Takaie, personal communication). The genus Keroplatus contains 26 species worldwide, of which the following 5 species have been reported to produce faint light at the larval and pupal stages: K. nipponicus (distributed in Japan; "Nippon-HirataKinoko-Bae" or "Mitsuboshi-Hirata-Kinoko-Bae" in Japanese) (Fig.…”

“…The larvae of Arachnocampa spp. and O. fultoni attract and prey on phototactic invertebrates by emitting luminescence and catching prey insects in sticky threads excreted by the larvae (Fulton, 1941;Meyer-Rochow, 2007). By contrast, the Keroplatini species (including luminous and non-luminous species of Keroplatus and Mallochinus) are spore-feeders, constructing a sheet web at the surface of fungi and feed on spores (Kato, 1953a;Matile, 1997) (Fig.…”

“…(Keroplatini, Keroplatinae) occurs sympatrically with K. nipponicus in Hachijo Island, also feeds on spores (Matile, 1997), and is non-luminous. On the other hand, non-luminous Orfeliini species are generally predatory (Matile, 1997;Evenhuis, 2006), and some of them are reported to trap prey with vertical sticky threads like Arachnocampa and O. fultoni (Jackson, 1974;Gould, 1991;Meyer-Rochow, 2007). A phylogenetic analysis based on morphological characters suggested that the ancestral state of the Keroplatidae was predaceous and the sporophagy in the Keloplatini was acquired secondarily (Matile, 1997).…”