Ecology of the New Zealand glowworm Arachnocampa luminosa (Skuse) (Diptera : Lycetophilidae) in tourist caves at Waitomo

Abstract

The New Zealand glowworm Arachnocampa luminosa (Diptera: Mycetophilidae) provides the national tourist industry with a unique attraction. The Glowworm Cave at Waitomo has an international reputation for the bioluminescent display produced by A. luminosa. The aim of the present study was to investigate glowworm ecology in the tourist caves at Waitomo, the results to provide factual information so that scientifically sound management procedures could be devised to ensure the long term survival of the population. The literature on all aspects of A. luminosa is reviewed. A continuous cycle of development occurs with most stages present throughout the year. However, the majority of the larval population pupates in late winter/early spring, producing a new generation in spring/early summer. There are five larval instars; the time for individual development in the Glowworm Cave varies considerably but is estimated to take 5 months on average. Distribution of glowworms is dependent on an adequate food supply, cool, moist climate and a suitable horizontal rock surface. Their diet consists of chironomids with some tipulids, ephemeropterans and trichopterans, most of which emerge inside the cave. Factors likely to influence distribution and productivity of benthic fauna in the cave are reviewed, including the importance of flooding and stream drift fauna in restocking the cave. Mortality is caused by two species of opiliones, cannibalism and a fungal pathogen identified as Tolypocladium sp. (Moniliales). Preliminary experiments with Tolypocladium indicate that the higher temperatures of the Glowworm Cave may be responsible for the prevalence of the fungus compared with non-tourist caves in the district. Observations on cave climate showed that the Glowworm Cave now has a higher range of temperature and relative humidity compared with earlier records and non-tourist caves at Waitomo. This is attributed in part to the free flow of air that occurs between the two entrances of the cave and the outside atmosphere. Reasons for the decline in the glowworm display that has occurred in the past few years are discussed. The installation of an open grille on the Top Entrance of the Glowworm Cave in 1975 is suggested as one of the main factors responsible. Future research projects are mentioned, together with recommendations for cave management related to glowworm ecology.