Introduction

The New Zealand glow-worm, Arachnocampa luminosa (Skuse) is one of the most interesting of our native insects, and yet very little is known about it. Glow-worms occur throughout New Zealand in limestone caves, unused mining tunnels, along stream banks, in damp bush-clad ravines, in damp, shady crevices and under tree fern fronds in rain forest, often forming quite impressive displays with their myriad twinkling bluish-green lights. The Glow-worm Grotto in Waitomo Cave has become world famous because of the tens of thousands of A. luminosa larvae which live on the walls, ceiling and stalactites of the Grotto. (Plate 27.)

When these insects were first observed, it was thought that they were related to the European glow-worm Lampyris noctiluca (Coleoptera, Lampyridae). An early record of them occurs in a Report of the Auckland Institute. Section 7, from the first meeting on May 29, 1871, states: “The Rev. A. G. Purchas exhibited the female insect and larvae of one or two species of Lampyridae which he had obtained from some of the drives on the Thames goldfields. He stated that their luminosity in some cases was most remarkable.” (Anon 1872).

In 1886, Mr. E. Meyrick published a note on some Auckland specimens of the glow-worm, which he considered to be predaceous coleopterous larvae belonging

to the Staphylinidae. However the editors of Ent. mon. Mag. added as a footnote: “There is distinct necessity for further information (with examples in fluid) respecting the animal noticed above. The larvae of Staphylinidae are ordinarily so like the perfect insect in form (allowing for absence of elytra, etc.) that we venture to doubt the connection of the animal with that family.”

In 1886, as the result of an examination of adult flies submitted to him by G. V. Hudson, Baron Osten-Sacken stated that the glow-worm belonged to the Mycetophilidae or fungous gnats. In 1890, it was described by Skuse as Bolitophila luminosa. In 1885, Hudson commenced studying the glow-worm, and from then till the time of his death in 1946, he was the main contributor of information concerning the habits of this insect. His material was obtained from the banks of a stream in the Botanical Gardens, Wellington.

On the basis of a number of important differences in the wing venation of the adult fly, and also the form and habits of the larva, Edwards (1924) erected a new genus for the species luminosa choosing the name Arachnocampa because of the “spider-like habit of the larva, forming webs and using them for the capture of insect prey.” In this respect Edwards claimed “the insect differs not only from all other Mycetophilidae, but from all other known dipterous larvae”. In 1927, Tonnoir and Edwards studied the Mycetophilidae of New Zealand and found Arachnocampa luminosa to be the only luminous species in the family.

In 1959, Gatenby referred luminosa back to the genus Bolitophila. Harrison (in press) however, is of the opinion that the genus Arachnocampa is valid. Further, he has examined numerous specimens from caves, tunnels and bush throughout New Zealand, and considers that in spite of the variation in size, they all belong to the species A. luminosa (Skuse).

The main study area for this paper has been the Glow-worm Grotto of Waitomo Cave, where the insects were under daily observation for most of 1955. Since then several short trips have been made to this cave. A Waitakere waterworks tunnel and the Parnell tunnel, Auckland, have been used as subsidiary study areas. Trips have been made to the limestone caves at Waipu, North Auckland; Ruakokopatuna; Wairarapa; and Rockville, Nelson, and to the Thames gold mines, as well as to Hudson's original site in the Botanical Gardens, Wellington, in order to study A. luminosa under natural conditions.