Mycetophilidae - undet. sp.
Size: (larva; not measured; approx. 12 mm)
Group Guild Status
Eutroglophile Predator Rare
Fungus gnats in the family Mycetophilidae are small, delicate flies that are often common in caves. They typically occur in association with organic materials near cave entrances, or on such materials that have been washed into caves, where the larvae feed on fungi present on the decaying materials. There are a few species with predaceous larvae.
We have a single record of a rather large (approximately 12 mm long; not measured) mycetophilid larvae (Photo 1) from beneath a cobble (approximately 3” x 4” x 6”) on the clay floor in Grand Central Station (Photo 2). The cobble is located a couple of meters from the Environmental Monitoring Station, and was originally embedded to about one quarter of its depth in the damp, clay-soil substrate. The animal was discovered by SW during our searches in the area on December 18, 2010. Based on its size we assume the animal was mature. It had created a linear mucous runway with many finer lateral mucous strands that covered much of the irregular clay-soil substrate beneath the cobble. Easily visible beads of mucous were irregularly spaced along many of the strands. The function of the beads is probably for trapping of microfauna, which would indicate a predatory habit of the larvae. Larvae that create mucous webs occur in three subfamilies of the Mycetophilidae; Diadocidiinae, Keroplatinae, and Sciophilinae, but only the Keroplatinae are known to contain predatory species. Mucous used to create the webs are derived from salivary excretions of the larvae. The extremely slender, smooth, oligochaete-like (worm-like) body form of this animal along with its mucous spinning habit and probable predatory nature likely place it within the Keroplatinae (Vockeroth 1981).
We monitored the larva monthly between December 2010 and June 2011 (except February), hoping to eventually find that the animal had pupated so we could retrieve the pupa and rear it out in the laboratory. This would provide us with an adult specimen for identification. Unfortunately, when we checked the site on June 11, 2011 the larva and its mucous web network were entirely gone. We searched for the pupa but were unable to locate it. Without a specimen of an adult we cannot further place this species.
Larvae of a few species in the Keroplatinae, notably the “glow worm” species at the Waitomo Caves in New Zealand, possess light-producing (luminescent) tissues that are used to attract prey (Vockeroth 1981). Because the species in Kartchner Caverns likely belongs to the Keroplatinae, we thought we should conduct a test to see if the larva emitted any visible light. We took a 10 minute open-shutter photograph of the animal on April 9, 2011, but no luminescence was detected. We were not really surprised by this result since the larva had spun its web beneath a floor feature where emitted light would be unlikely to be effective in attracting prey. The larvae at the Waitomo Caves spin their webs on the ceiling of the cave where their emitted light is readily visible to, and successfully attracts, potential prey.
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