Evolution of the Glow Worm
The genus Arachnocampa (Glow Worm) is within the family Keroplatidae (Fungus Gnats). The oldest fungus eating gnats date back to 200 million years ago. So how did a fungus-consuming insect living inside fungi evolve into a carnivorous insect that uses a highly developed predatory system which includes bioluminescence to attract prey and a sticky web-structure to entrap its prey?
Some gnat species lay their eggs inside fungi. After the larvae hatch they remain inside and consume the fungi (group 1). In other species, when the larvae hatch they build webs on the underside of the fungi and trap fungal spores on which they feed (group 2). More advanced species not only eat the spores but also consume minute invertebrates that are also trapped in the webs (group 3). Then there are other gnats which are totally carnivorous (group 4) (Meyer-Rochow 2007). |
These three different diets support the theory that it may have been a multi-stage evolutionary process - group 1 evolved into group 2 which developed the ability of spinning silk to build webs. Group 2 evolved into insects that eat both fungi and invertebrates and finally group 3 evolved into insects that were wholly carnivorous.
It is only in this last group that bioluminescence is important to attract invertebrates to the web. In habitats where there is an abundance of small invertebrates (e.g. Central and South America) gnats are not bioluminescent. It is only in Australia and New Zealand where there is a scarcity of prey that gnats developed the ability of bioluminescence to attract prey to their webs (Meyer-Rochow 2007). |