Go to National Library of New Zealand Te Puna Mātauranga o Aotearoa
Volume 88, 1960-61
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Life History

Egg. No difference was observed in size or colour of eggs laid by bush, tunnel or cave female flies. The egg is spherical in shape and 0.75 mm in diameter (Plate 28, fig. 1). When deposited it is cream in colour, but within a few hours it changes to either a light brown or an orange-red colour. Larvae hatch from both types. After hatching, the empty chorion is usually a reddish-brown colour. The eggs are slightly sticky and adhere to the substratum. They are usually deposited directly onto the limestone walls of caves, where thousands have been observed. A few may be deposited on empty pupae. According to Gatenby (1960), ‘they may be stuck to the substratum by an orange-coloured cement’. Although several thousand eggs have been examined by the author both in the field and in the laboratory, no trace of this cement has been observed. Many of the eggs are eaten by opiliones and isopods.

Eggs deposited on the ceiling in the Demonstration Chamber, Waitomo Cave, in early July, 1955, were segregated under a glass lid; they commenced hatching 22 days later. Another series of eggs in a box in another part of the cave took 24 days to hatch. Eggs laid on damp cotton wool in the laboratory took 20 days to

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General View of Glow-worm Grotto in Waitomo Cave.
Photo by courtesy of National Publicity Studios.

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Fig. 1—Eggs of A. luminosa Natural size 0.75 mm in diameter.
Photo: J. W. Endt.
Fig. 2—Larva of A. luminosa emerging from the egg.
Photo: S. A. Rumsey.
Fig. 3—First instar larva of A. luminosa suspended from the ceiling in Waipu Cave.
Photo: S. A. Rumsey.

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fig. 1.—Larva of bush glow-worm near Aranui Cave, Waitomo.
Photo: S. A. Rumsey.
fig. 2.—Larva of cave glow-worm on wall of Grotto in Waitomo Cave.
Photo: J. Pybus.

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fig. 1.—Larva of A. luminosa suspended vertically from the ceiling in the Swanson Tunnel, Auckland, just prior to pupat.ion.
Photo: S. A. Rumsey.
fig. 2.—Female pupa of A. luminosa showing attachment of suspensory cord to the dorsal surface of the thorax.
Photo: S. A. Rumsey.
fig. 3.—Male pupa of A. luminosa. Photo: S. A. Rumsey.

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fig. 1.—Larva of A. luminosa removed from its nest.
Photo: S. A. Rumsey.
fig. 2.—Ventral aspect of female pupa of A. luminosa.
Photo: S. A. Rumsey.

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fig. 1.—Pupa of A. luminosa suspended from ceiling in Waitomo Cave. All larval fishing-lines have been removed.
Photo: J. Pybus.
fig. 2.—Pupa of A. luminosa hanging amongst a dense mass of larval fishing-lines in Waitomo Cave.
Photo: J. Pybus.

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fig. 1.—Male fly of A. luminosa emerging from a pupa on the ceiling of Waitomo Cave.
Photo: S. A. Rumsey.
fig. 2.—Male and female flies of A. luminosa in copula. Both flies are clinging to the empty female pupal case in the centre. The female fly is on the left and the male fly on the right. The eggs are visible through the body wall of the female.
Photo: S. A. Rumsey.

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fig. 1.—Male fly of A. luminosa on ceiling in Grotto of Waitomo Cave. The tip of the abdomen is characteristically raised above the rest of the body, and the wings are folded over the thorax and anterior part of the abdomen.
Photo: S. A. Rumsey.
fig. 2.—Two male flies of A. luminosa attempting to copulate with a female fly which has just emerged from a pupa. They are suspended from the ceiling in the Grotto of Waitomo Cave.
Photo: S. A. Rumsey.
fig. 3.—View of same three flies from opposite side, showing male and female in copula, while other male fly attempts to separate them.
Photo: S. A. Rumsey.
fig. 4.—Female fly of A. luminosa ovipositing on the ceiling in the Grotto of Waitomo Cave.
Photo: S. A. Rumsey.

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fig. 1.—Female A. luminosa bush fly on left and cave fly on right. Both are photographed to the same scale.
Photo: S. A. Rumsey.

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fig. 1.—Dorsal view of male fly of A. luminosa Photo: S. A. Rumsey.
fig. 2.—Dorsal view of female fly of A. luminosa. The light organ is glowing in the anal segment.
Photo: S. A. Rumsey.

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fig. 1.—Larva of A. luminosa on wall of old Railway Tunnel, Parnell, Auckland, showing long braces for attachment of nest to the tunnel wall. The larva is inside the right half of the nest. Scale X 2.25.
Photo: S. A. Rumsey
fig. 2.—Larvae of A. luminosa in Demonstration Chamber, Waitomo Cave, showing very long fishing-lines.
Photo by courtesy of National Publicity Studios.

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fig. 1.—Larvae of A. luminosa removed from the Grotto, Waitomo Cave, after having been attacked by the fungus Beauveria sp.
Photo: J. W. Endt.
fig. 2.—Pupa of A. luminosa which has been attacked by fungi, hanging from the ceiling in Waitomo Cave.
Photo by courtesy of National Publicity Studios.

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hatch at room temperature. These results indicate that the incubation time for the egg is between 20–24 days.

In the later stages of development, a dark spot, the heavily chitinised head of the embryo, is visible through the chorion. At hatching, the chorion splits open at the anterior pole, and the split continues laterally threquarters of the way down each side of the egg (Plate 28, fig. 2). Eggs have not been observed to luminesce during any stage of their development.

Larva. A newly hatched larva is cylindrical in shape. It varies in length from 3–5 mm and is about 0.33 mm in width. The larvae grow over a period of several months till they reach a length of about 30 mm in the bush variety, and 40 mm in the cave variety (Plate 29, Figs. 1, 2).

Immediately on hatching the larva emits a bright light. Were it not for its light, its transparency and size would make it very difficult to find. The larvae spread out over the ceiling of the cave or tunnel and commence building nests and letting down long sticky threads or fishing-lines. At the end of three weeks a cave larva is about 6 mm in length and 0.5 mm in width, with fishing lines about 50 mm long (Plate 28, fig. 3). These observations differ from those of Gatenby (1960) who states that very young larvae have “no vertical lines, only a runway, and on banks, always a hiding place as well”.

Larvae are not necessarily confined to their nests, but often move about for considerable distances over the substratum seeking a site for a new nest. Because of this, it is very difficult to study them unless they are caged, and consequently the complete time for larval development has not so far been recorded. It is probably about eight or nine months.

Pupa. At pupation the larva shrinks in size and becomes translucent. It removes the fishing-lines and braces of its nest and suspends itself vertically by a long thread, approximately the same length as the pupa (Plate 30, fig. 1). Then it pupates (Plate 30, figs. 2, 3; Plate 31, figs. 1, 2). This is a gradual process, which may take up to 24 hours. It has been observed by the author in Waitomo Cave, in Waipu Cave and in the Waitakere tunnel, Auckland. In captivity one larva pupated at a 45′ angle, being still partly suspended by braces from the old larval nest.

The suspensory cord of the pupa extends from the ceiling to the region of the thorax. When Hudson described the pupa in 1886, he considered this cord to be part of the pupa itself. Edwards (1933) however, considered the cord to be part of the larval web. This, he thought, on drying gave the appearance of being part of the pupa. Gatenby (1959) believed the cord to be the runway of the snare. The author believes that the thread is formed from the larval nest and its supports. In Plate 6, figs. 1 and 2 show that the thread is made up by the fusing together of a number of branching threads.

There are two different arrangements for pupation. Occasionally the pupa hangs suspended among a surrounding curtain of fishing-lines (Plate 32, fig. 2). More commonly the pupa is isolated or suspended in the centre of a circle 7–10 cm in diameter (Plate 32, fig. 1). The periphery of the circle consists of a row of fishing-lines approximately 5 cm in length. The significance of this circle is not known, but it may act as a protective shield to the pupa, the clear space preventing the fly from becoming entangled in long fishing-lines of other larvae after it emerges.

In July, 1959, 9 male and 13 female pupae were collected from Waitomo Cave, one female pupa was collected from the bush at Waitomo, and 12 male and 13 female pupae from the Waitakere tunnel. The cave forms were all larger than the bush and tunnel forms (Table III). No other differences were noticed.

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Table III.—Variability in Length of Pupae of Arachnocampa Iuminosa (Skuse).
Male Female
Number 14 21
Cave Type Mean 13.25 mm 16 mm
Range 12–14 mm. 15–17.5 mm
Standard Deviation 1.3 0.74
Number 12 14
Tunnel and Bush Type Mean 10.8 mm 12.5 mm
Range 10–11.5 mm 12–14 mm
Standard Deviation 0.54 0.62
Significance of difference All 0.001

Sexual differentiation is evident in the pupal stage. The female pupa is larger and stouter than the male. It possesses two prominent papillae (Plate 31, fig. 2) at the distal end of the abdomen. In the male these papillae are noticeably smaller in size.

According to Norris (1894), who observed A. luminosa in the Botanical Gardens, Welligton, the male and female pupae are both luminous. He says, “The male is luminous in the pupa until the last two or three days before it hatches.” Until the present author commenced studying A. luminosa, no other worker on this insect since Norris had observed a luminous male pupa. On many occasions, at Waitomo, Waipu and the Waitakeres, male and female pupae have been observed to glow throughout all stages of their development. The pupal light is very intermittent. As in the larva, the luminous organ is situated in the last abdominal segment. Hudson (1886) considered that the light from the pupa was much fainter than in the larva, but on this point the author disagrees. While shining much less frequently than in the larva, the light can be fully as brilliant. One female pupa collected in the bush at Waitomo first attracted attention because the brilliance of its light was far greater than that of any of the surrounding larvae.

Luminescence of the female pupa is particularly noticeable during the latter period of its development. When the pupa is gently touched or rocked, the light flashes on immediately for a few seconds and then goes out again. Thus, when a male fly alights on a female pupa, the light goes on. Male flies have often been observed clinging to female pupae, but female flies have never been observed clinging to male pupae. When a female fly is about to emerge it is common to find one, two, or even three male flies clinging to the pupa. The length of the pupal period is twelve to thirteen days. During the last two or three days before emergence of female flies, eggs become visible through the transparent pupal skin.

Imago. The imago emerges head-first, pulling its wings and legs after it. This may occur at any time of the day, and has been observed by the author on several occasions. It is a fairly slow process taking up to an hour or longer, the fly often glowing brilliantly the whole time.

The anterior end of the pupa is split open by the dilated thorax of the imago, and the thorax emerges followed by the head and anterior segments of the abdomen. The three pairs of legs lie against the abdominal sternites, and the antennae are

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directed posteriorly towards the legs. The fly emerges by muscular contraction and expansion of the body and wriggling of the legs. In the female the body is distended by eggs which are visible through the body wall (Plate 33, fig. 2). The body of the male is smaller and much narrower. The tip of the abdomen is the final part to be withdrawn from the pupal case. (Plate 33, fig. 1.) The imago hangs head-down from the pupal case till it is dry; then it turns through 180° and hangs from the pupal case till its wings are strong enough for it to fly.

At emergence, the thorax of the imago is a creamy pink colour with a number of black setae on it arranged in rows. The abdomen is pale fawn and transparent. Over a period of several hours, the colour gradually intensified to dark brown with a dorsal, median fawn stripe on the thorax and lateral fawn stripes at the anterior end of each abdominal segment. The colouring is more strongly marked in the male than in the female.

Both male and female flies (Plate 36, figs. 1, 2) are very sluggish in flight. Male flies, however, are the more active of the two. They move only comparatively short distances, and consequently are easily caught. Both flies make a buzzing noise, that of the female being louder than that of the male. When at rest, the wings are folded over the thorax and abdomen (Plate 34, fig. 1).

There is a marked difference in size between A. luminosa flies living in caves and those living in tunnels or in the bush (Plate 35, fig. 1). This may be attributable to the greater food supply for larvae in caves (Table IV). The size ratio between the sexes remains stable.

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Table IV. —Variability in Length of Flies of Arachnocampa luminosa (Skuse).
Male Body Male Wing Female Body Female Wing
Number 17 17 16 15
Cave Mean 13.3 mm 7.9 mm 14 mm 10.2 mm
Type Range 12–15 mm 7–8.5 mm 13–16 mm 9–12 mm
S.D. 0.97 0.46 0.85 0.84
Number 9 9 12 12
Tunnel & Mean 10.6 mm 6.5 mm 11.4 mm 8.2 mm
Bush Type Range 9–11 mm 6–7 mm 10–13 mm 7.5–9 mm
S.D. 0.73 0.50 1.08 0.78
Significance of Difference All 0.001

At Waitomo Cave, male flies were always far more numerous than females; while in the Waitakere tunel the reverse appeared to be the case. On June 30, 1959, a count of pupae and flies in the Waitakere tunnel showed 37.5% of the population of about 100 were males and the rest females. On July 16, 1959, a population of approximately 500 individuals in the Tunnel of Waitomo Cave consisted of 13.3% females and the rest males. The sex ratio of flies in the bush has not so far been determined.

Both male and female flies are intermittently luminescent at the distal tip of their abdomens. The light from the female is larger and brighter than that from the male. Hudson and Norris both observed luminous female flies. Hudson never

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saw a male fly. Norris (1894), however, saw several. He stated, “I have three males, and none of them was luminous in the imago.” Hudson suspected that the female's light was used to attract male flies, but he was unable to prove this. Gatenby (1960) collected one male and two female flies from Waitomo and observed that none of them glowed. He sectioned the abdomen of the male and stated, “The malpighian tubule connectives are present as usual, but are shrunken. This would appear to support the findings of those naturalists who have stated that the male is not luminescent.” Gatenby illustrated his paper with a sketch of the posterior part of the abdomen of a male fly and a section through the abdomen. His sketch does not resemble the posterior abdominal segments and genitalia of the male Arachnocampa luminosa fly described and figured by Harrison (in press), so that he could not have collected the male fly of A. luminosa. This would explain his statement, “The adult male has degenerate light organs in which collapse of the tubules and some aggregation of the nuclei has taken place.” The adult male fly is definitely luminous. This phenomenon has been observed by the author on numerous occasions. Luminous male flies have been collected from Waitomo Cave, Waipu Cave, and the Waitakere tunnel and also reared in the laboratory.

In February, 1955, luminous male flies were observed for the first time by the author and Mr. D. K. Turner. About 8 p.m. a male and female fly were removed from Waitomo Cave and placed in a glass container in the dark. An hour and a-half later, a faint light was observed through the glass. This proved to be coming from the male fly, which suddenly produced a bright light. This lasted for a few seconds and then dimmed again. About midnight the male was again faintly and continuously luminescent. No light was observed from the female. At 9 a.m. the next morning the female was shining brilliantly. No further luminosity was observed till midnight, when the male fly was once more brilliantly luminescent. The light soon faded when electric light was switched on, but reappeared faintly when the light was turned off. After that neither fly showed any further signs of luminescence. Several other male flies observed to glow in the cave were not removed for further observation. A male fly, removed as a pupa from the Waitakere tunnel and placed in a glass container, glowed intermittently in a darkened room from 5.30 p.m. to midnight.

On several occasions in Waitomo Cave luminous female flies have been observed on the wing. This does not appear to have been previously recorded. It was thought by earlier workers that A. luminosa flies never luminesced in flight.

It has been suggested by Gatenby (1959) that in A. luminosa “both male and female adults may be negatively phototropic, which would keep them clear of snares,” but Gatenby admits that he has never seen A. luminosa flies on the wing. If he had, he could not have failed to observe that they are both positively phototaxic, and are often caught in the fishing lines of larvae. In most cases this is not a serious problem, as they are usually powerful enough to break free.

Mating. During 1955, A. luminosa flies in Waitomo Cave exhibited two different types of mating positions. In the first, which was the more usual, the two flies hung from the pupal case. The abdomen of the male lay to the side of the female's and the tip was turned to effect coitus. (Plate 33, fig. 2.) The wings of the female were folded while those of the male were widespread.

In the second the two flies mated vertically, tail to tail. The male hung head down clinging to the empty pupal case from which the female had just emerged, while the female clung to the limestone wall. This was observed on two occasions.

In July, 1959, a male and female fly were put together in a glass container in the laboratory, and the whole process of mating observed. The female immediately settled on the side of a piece of paper, while the male flew round excitedly for several minutes till he found her. Copulation lasted for one hour thirteen minutes. For the first forty minutes their position was as described for the first mating position.

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Then the male tried to break free. While still remaining attached, they became extended end to end as described for the second mating position. Over a period of almost twenty minutes the male made numerous attempts to break free before he finally succeeded. The female was passive throughout. Thus the two mating positions observed in Waitomo were part of the one process.

The female usually mates as soon as she emerges, but copulation may not occur till several hours later. She often glows brilliantly when the male attempts to mate with her. Occasionally the male also has been observed to glow. Only one mating takes place.

Two or more male flies often hang from the female pupa waiting for the fly to emerge. Each attempts to fertilise her the moment the tip of her abdomen becomes free from the pupal case. The successful male has to fight off the attempts of the other males to separate him from the female. In Plate 8, figs. 2, 3, taken in Waitomo Cave, the unsuccessful male fly is shown clinging to the body of the female as it strives to separate the mating pair. In this particular case mating continued for seven hours. Fighting among several male flies over a female has been observed to continue for several hours.

To show that female flies can attract male flies from a distance, a newly emerged unfertilised female fly was placed on a stalactite in a part of Waitomo Cave where no flies had been seen for several days. Five hours later, the female fly was observed in the same position as when left, but she had now mated with a male fly.

Observations were also kept on another female fly that was not fertilised immediately she emerged. She used her light to attract a male fly, flashing it on and off till one arrived. Then she extinguished it and flew a short distance away. Having settled, she exhibited her light till she had succeeded in attracting him again. This pattern was repeated several times till mating was finally accomplished. Throughout the whole period the male fly did not glow.

The light in the female is used as a mating device to attract the opposite sex, while that from the male does not appear to be used in this connection. The light from the female is larger and brighter than that from the male, so that it would be possible for flies on the wing to distinguish between the sexes. This may help to explain why several male flies become attracted to the same female. It is possible that tactile and olfactory organs may also play important parts in the attraction of male flies to females in darkness.

After copulation the female fly can still turn her light on and off at will, but females seldom glow once egg laying has commenced. The length of life of the female fly can range from less than 24 hours up to 76 hours. Male flies usually live longer than females, and are capable of fertilising more than one female. They can survive up to four days.

Discussing the ability of the female fly to luminesce, Gatenby (1960) wrote, “there is reasonable doubt if this is done to attract the male, for if he is positively phototropic he is then in danger of being snared by the lights of the larvae.” Later in the same paper he wrote, “The female remains quiescent and shows her light till she has paired, and then the light fades away.” The second statement is correct.

Oviposition. Egg laying may commence almost immediately after fertilisation, or it may be delayed for several hours. During this time, the female flies about looking for a suitable spot to lay her eggs. Usually over 100 eggs are laid. Actual counts of eggs laid by single female flies isolated immediately after mating were 84, 93, 107, 112, 118, 130, 160, 160, 170, 170; an average of 130. Gatenby's (1960) statement that “the female can lay up to about eighty eggs,” was based on two female flies taken from Waitomo Cave. Both specimens were killed, and the eggs inside them counted. From these counts of 65 and 75, he deduced that “about 75 eggs” were laid. However, he appears to have overlooked that egg laying may have commenced before the flies were collected.

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When about to lay an egg, the female feels with the tip of her abdomen for a suitable spot. Having located it, she brings the tip of her abdomen back under the body. This is followed by violent contractions and flexing movements of the body. Then the abdomen is brought back to a normal position, and the tip gently touches the substratum depositing an egg. (Plate 8, fig. 4.) Each egg is deposited singly. Occasionally groups of up to six may be deposited in quick succession and adhere together. Egg laying is either continuous or sporadic over a period of from one to 24 hours until all eggs are laid. The female usually dies immediately afterwards. The eggs are laid in large numbers close together on the substratum. Over 30 eggs have been laid by a female fly in the seven minutes required to carry the caged fly the 300 yards from Waitomo Cave to the Hotel. As can be seen from Plate 8, fig. 4, the actual posture of oviposition in A. luminosa is quite different from Gatenby's (1960) drawing of how he imagined it might occur.

When kept in captivity in a test-tube, female flies usually laid their eggs on the cork, while those kept in a trough laid them on damp cotton wool in preference to glass.

In June, 1955, Mr. C. Voerman set up an observation box in one of the unfrequented corridors in Waitomo Cave. He placed male and female pupae in the box, and watched the flies emerge, mate and the females lay their eggs. Eggs were laid on the wooden frame of the box, on limestone slabs inside it, on wire suspending the limestone and on wire gauze at the back of the box. The wire gauze was covered with verdigris, yet the female clung to the wire with her legs, thrust the tip of her abdomen through one of the holes, twisted it round, and deposited eggs on the outside of the wire. Thus the female fly is apparently not selective in her choice of sites for egg-laying.

In the laboratory, unfertilised female A. luminosa flies have been observed to lay eggs. This was first recorded from a female fly that emerged from a pupa collected from the Waitakere tunnel. She was placed in a glass container with a male fly, but mating did not take place, and after about an hour she laid 16 eggs in quick succession. A short time later she died. The eggs were kept, but did not hatch.

Later, a female fly that had emerged from a pupa collected in the bush at Waitomo, was placed in a container with two male flies from Waitomo Cave. Mating did not take place, but over a period of an hour she laid 15 eggs. These were kept, but did not develop. No further eggs were laid, and four hours later she was dead.

It is possible, that unfertilised eggs are also laid under natural conditions, although this has not been observed. This suggests that although virgin females are capable of laying eggs, parthenogenesis does not occur.

Although spending all their time in total darkness, A. luminosa flies are diurnal rather than nocturnal in their behaviour. Mating and oviposition may occur at any time, but oviposition appears to be more common during daylight hours. Light itself does not stimulate this activity, as in all observed cases the flies were kept in total darkness.