Biology 342 Fall 2012
Emily Agan, Christina Barrett
The Ontogeny of this behavior has never been studied directly, so it is impossible to know if this trait is innate or learned, or how this trait might change over the animals lifetime, except to the extent that they use these predatory techniques throughout only the larval stage, as outlined below. However, despite the lack of formal study, a conclusion can be tentatively extrapolated from the existing information.
The ability of the larvae to construct these silken-mucus lain lines the same way every generation right from emergence strongly suggests that this is an innate trait, that the ‘worms’ know instinctually. The entire process of trap building, and luring requires no learning, or even experimentation: the larvae figure it out immediately and are usually catching live prey and drawing them up to be devoured on the cave roof be the end of their first day of life.
In order to test this hypothesis experimentally, one could take eggs from their laying ground and isolate them, either in a lab setting or a natural, but secluded, habitat, and observe whether the larvae exhibited the same behavior in the absence of cues from other glowworms, or their specific environments. If the behavior is innate a larva should be able to begin trap building and luring immediately, and the same way it would in natural circumstances. If the behavior is learned, the ‘worm’ should be unable to preform the task as observed in nature in the absence of the cues it would learn from.
Observations of glowworms in the wild, then, point to their feeding strategy as an innate, genetically determined trait.
Life Cycle of the Glowworm
A Humble Beginning...
A. luminosa live for about 10-12 months depending on environmental factors such as temperature and humidity, and food availability, but spend the majority of that time (9-11 months) in the larval stage. The common name “glowworm” refers to the larval stage of A. luminosa and other similar bugs which are worm-like in their larval form, and glow, but are not technically worms.
A. luminosa begin their journeys as one of about 130 siblings laid in the same spot after about 7 and 9 days of developing in small (0.75 mm diameter) A. luminosa eggs. Upon hatching the small (3-5 mm long) larvae emerge.
Immediately upon emerging from their eggs the larvae attempt to find their first meal immediately, sometimes converting to cannibalizing their siblings in their hunger. Most often though, the larvae simply begin preparing their traps in order to catch their first meal as quickly as possible. The larvae find a damp high spot along the roof of their cave habitats and lower lines of silk with interspersed droplets of mucus in order to capture prey in the sticky matrix. Finally the larvae activate their light organs - the lure - and wait to feel the vibration of the live prey falling victim to their own phototaxis.
The bioluminescence itself is clearly an instinctual behavior, as the worm will glow from from hatching (and has sometimes been reported to glow through the egg encasement) and will glow as long as there is food to sustain it (Meyer-Rochow, V. B. 2007).
Sourced from Tyler's Naturalist Blog
During the larval stage the critters grow immensely (about ten times its size at hatching) over the course of 9 months and 4 molts. Finally the larvae pupate, a transitional state that last for 6 to 7 days and is also intermittently luminescent for both sexes, although only female A. luminosa glow in their adult phases.
Sourced from Meyer-Rochow, V. B. (2007).
Once the fully formed adults emerge the biological clock is ticking. In this state, the flies are geared towards only one end: reproduction. Both sexes are geared with wings to help them cover distance and find mates, although females’ flight is hindered by the extra weight of the eggs she is already carrying. The females will only live for a matter of 2 to 3 days; the males have closer to a week, and for this entire time no adult A. luminosa feed, or even have the biological equipment to eat. After successful copulation, females will lay their eggs close to where they lived, and will die shortly thereafter. This entire process can be sumarized in the figure below (Meyer-Rochow, V. B. 2007).