Biology 342 Fall 2012
Emily Agan, Christina Barrett
The Use of Bioluminscence as a Lure in the New Zealand Glowworm
“We are all worms. But I believe that I am a glowworm.”
Winston Churchill, worm connoisseur that he might have been, did not have the Arachnocampa luminosa, a species commonly referred to as a ‘glowworm,’ quite pegged. A. luminosa is actually a type of fly, that in the larval stage appears similar to a worm and has the ability to luminesce, or emit light. It is this stage of life that holds to most interest for scientists today.
Winston Churchill’s famous quote does reveal a long-standing fascination with the ability of some organisms to bioluminesce, but to A. luminosa, a species of New Zealand’s cave dwelling glowworms, the ability is not an oddity, or a parlor trick, but a matter of every day survival. The glowworms live on cave roofs and lower silken lines by the hundreds from their elevated positions, vomiting tear drop sized balls of mucus at regular intervals. When the trap is complete, the larva will then glow and wait.
It doesn’t have to wait for long.
Small local flies are drawn to the only sources of light in the dark cave due to their own natural phototaxis, or attraction to light, and get caught in sticky wet webs, twitching wildly and drawing the attention of the predator above. The next stage of the feeding behavior has been triggered, and the hungry larva slowly ingests the entirety of the vibrating silken line, until it has swallowed its unfortunate prey. The line is restrung, and the trap waits for its next light-loving victim.
This entire process was captured on tape in BBC's nature documentary series, Planet Earth, in their episode on cave habitats.
A. luminosa’s unique method for capturing prey combines the methods of trap building and luring, seen in nature as separate predatory strategies in many species. Many species of spiders and ants create traps using a combination of artificially built natural structure, such as the construction of webs around a preexisting infrastructure of leaves and branch. Bioluminescence is used a lure by several underwater species that have no way of create a trap in their deep sea environment, but rely on their own reflexes upon prey arrival. But the glowworm can do both, and combines these strategies with amazing effectiveness and efficiency.
Finally, scientists strive to explain this (and most) behaviors using a series systematic questions, which are coined Tinbergen’s four questions, after their originator, Nikolaas Tinbergen. The questions address the causation, ontogeny, adaptive value and phylogeny of a specific phenotype or behavior.
Sourced from Another Reed Website!
This website will seek to answer each question in turn, as defines in the figure above. We will attempt to show how the trap and lure behavior is physically preformed, whether it is learned or innate, the advantage of such a behavior to reproductive lifetime fitness, and how this behavior evolved.
This website created by Emily Again and Christina Barrett for Suzy Renn’s Animal Behavior course (342) at Reed College.