Art. XXVI.—Bionomic Observations on certain New Zealand Diptera.
[Read before the Otago Institute, 8th June, 1909.]
This papaer is composed from the notes on the Diptera which I have collected in Otago during the last two seasons.* The species dealt with are to be found described in the “Synopsis of the Diptera Brachycera of New Zealand” (Trans. N.Z. Inst., vol. xxxiii), by the late Captain Hutton; those described elsewhere have the references attached. Only a few of the more common species are figured in colour in this paper, as diagrams and coloured plates of all the species will appear later in a series of papers which I hope to publish, dealing with both new species and those flies already described by Captain Hutton. Where it is deemed necessary, I insert a brief account of the general characters and habits of the families.
I am indebted to Professor Benham for his invaluable suggestions during the preparation of this paper.
To avoid repetition I shall here give a description of the general features of the localities mentioned:—
Ocean Beach forms the ocean side of the isthmus connecting Otago Peninsula with the mainland. This isthmus, which is about a mile in width, is formed, for the most part, of blown sand and alluvium, and is bounded on the opposite side to the beach by the mud-flats at the head of Otago Harbour. The sandhills of Ocean Beach are covered with lupinbushes and marram-grass.
Tomahawk is separated from Ocean Beach by Lawyer's Head. Behind the sandhills of Tomahawk is a lagoon into which run the streams from the surrounding hills; the overflow finds a course over the sand to the sea. Lupin-bushes and marram-grass abound.
Purakanui is the district to the north of Otago Heads. The coastline of this locality is formed of a series of precipitous headlands with intervening sandy beaches, behind each of which there generally exists a mud-flat or swamp fed by streams originating from the hills. Of these, Murdering Beach is a short strip of sand, surrounded by steep hills, and backed by a swamp in which rushes and other forms of vegetation grow. Long Beach is a stretch of sand of considerable length, and an extensive area of cultivated land (often under water) exists behind the sandhills. Mapotaki Beach faces the north (the last two face the north-east), and is somewhat similar in form to the preceding, differing in the fact that the sea gains an entrance to the mud-flat by a small stream which runs across the beach after draining the swamp. The surrounding hills of Purakanui are in places covered with what remains of the native vegetation.
Mount Cargill (2,232 ft.) is situated toward the north of Dunedin, and is still more or less covered by the native bush, which is either being felled or burned off.
[Footnote] * Owing to the loss of a note-book, the remarks concerning several of the species mentioned below are somewhat meagre. However, since these observations went to press, additional facts have been collected for another paper, which I propose to publish as soon as possible.
The Nuggets is a rocky headland about sixty-five miles south-west of Dunedin. To the north of this headland are extensive stretches of sandy sea-beaches backed by dense native undergrowth; in certain places swamps exist.
Barewood is situated inland, about twenty-five miles north-west of Dunedin, and about 820 ft. above sea-level. This locality is well named, the vegetation consisting of tussock, matagouri scrub, and a small plant with a yellow flower called the Maori onion (Bulbinella Hookeri). The Taieri River runs, in a deep gorge, through this locality.
Taieri Mouth is the name applied to the beach where the Taieri River meets the sea, about twenty-two miles south-west of Dunedin. This beach has much the same formation as that at the Nuggets.
Series O R T H O R R H A P H A B R A C H Y C E R A.
The members of this family inhabit flowers, and very in size, some being small, while others are inclined to be large. Certain of the species are distinguished by the bright green of the abdomen.
This is a small species measuring about 4 mm. in length. I found a single specimen at the head of Mapotaki Bay in November (1907); this fly was resting on a bramble-bush growing near the mud-flat, which is covered by the sea at high-tide.
Odontomyia chloris. (Plate XXVIII, fig. 1)
Common during the season, but not to be observed in swarms. In January (1908) I captured two specimens on the sea-beach of Taieri Mouth, where, I think, they had been blown from the swamps behind the sandhills. The weather was very warm, sunny, and windy. At Roslyn, during February of the same year, I captured another specimen, which was at rest on a daisy exposed to the sun. Two more specimens were found in January (1909) on Murdering Beach, and under similar weather conditions to the preceding. Specimens of this species are common in gardens, and may be found in most situations.
About the same length as the preceding, but sometimes smaller, the sexes differing in size. One bright, warm, and windy day during December (1908) I captured a single specimen at Barewood, Central Otago.
Fam. Asilidæ (Robber-flies).
Robber-flies, the most predaceous form of Diptera, are, as a general rule, large insects which prey upon others. When a victim is captured, the aslid bores a hole in the thorax by means of the horny proboscis, and thus obtains the nutritive portions of the prey.
Saropogon fugiens. (Plate XXIX, fig. 4)
During December (1907), at Taieri Mouth, this fly was exceedingly common. A number were captured among long grass near the bush. Vast numbers were found lying in a helpless condition at the margin of the sea, into which they had been blown by a strong offshore wind. I
observed one specimen, which had been wet, struggle to a dry piece of sand (about a quarter of an inch in diameter), and, mounting this, stand up with its feet held closely together and stretch out its wings to dry in the wind. In this, I think, it would have been successful had it not happened that a wave coming up a little farther than usual enveloped the fly, and carried it back into the struggling mass of its fellows. As the tide went out there was left stretching along the beach a sinuous line composed of these flies and also representatives of other genera. Enormous numbers of Diptera are thus destroyed. When walking along Ocean Beach one day I was surprised to see a black continuous band stretching along the sand as far as the eye could reach; on examining it I found this dark line to be composed of myriads of small black flies belonging to the family Mycetophilidœ, which were evidently carried there by a strong breeze.
Found at Taieri Mouth in company with S. fugiens. I also captured a single specimen on Mount Cargill during February (1909); the weather was very hot and sunny, there being no wind.
Itamus varius. (Plate XXIX, fig. 6.)
Captured on the sea-beach at Taieri Mouth, January (1908). This fly was not then common: only a single representative was captured in this locality. It was more abundant at Barewood, Central Otago, where I captured several during December (1908). The specimens observed at Barewood would, when approached, either fly for a short distance and again alight or run into a tussock.
The members of this family are not so active as those of the Asilidœ, but otherwise they agree in habits.
Length, 16 mm. I captured a single specimen at Taieri Mouth, January (1908), and two on Murdering Beach during the same month of the following year. This species is not common; it is to be found on sandhills during warm weather.
Smaller than the preceding, being about 10 mm. in length. This species does not appear to be common, since only two specimens were found, on ivy, in the sun, at Roslyn, November (1907).
These flies are predaceous in their habits, and are seldom found in barren situations, on account of the presence in these localities of their more powerful allies, the Asilidœ.
This is a small, abundant species, about 4 mm. in length, to be found in swarms hovering over bushes and flowers from November to February.
The males of this family bear sexual ornamentations on the legs, head, the third joint of the antennæ, as well as on other parts. The species of this division are small.
Very common in the bush at Taieri Mouth during January (1908). These flies were found, basking in the sun, on tree-trunks. I captured only two at Murdering Beach in January (1909), and these were resting on rushes which grew in a swamp behind the sandhills.
Series C Y C L O R R H A P H A A S C H I Z A.
Fam. Syrphidæ (Hover-flies).
The members of this family are both large and small, and are beautifully coloured with yellow and green. They are usually found hovering over flowers in the sun, and can be recognised by their mode of flight alone, which is described thus by Kirby: “They hover motionless in the air, and, if alarmed, dart off with a rapid motion that the eye cannot follow, and hover again as soon as they stay their course.”* The larvæ are beneficial to gardeners, as they destroy large numbers of injurious insects.
Eristalis tenax (introduced).
Abundant everywhere from February to March; also found—but in decreasing numbers—in April and May. This species is found hovering about flowers in the sun. When it alights, the abdomen may often be seen moving up and down, and the wings are held in such a position as to expose the abdomen. I observed a specimen feeding on the pollen of a dandelion: the fly took hold of the stamen of a flower with its proboscis—which appears to be bifid at the distal extremity—and passed it once or twice up and down the stamen in order to rub off the pollen. After this operation had been indulged in two or three times, the fly held out its proboscis at full length, and moved the bifid portion as if it were in the act of tasting. Another specimen I observed to rest on the broken end of a holly-twig, by alighting so that the sharp edge of the broken twig came between the bases of the fore and middle legs; the fly steadied itself with the posteriortarsi pressed against the sides of the twig, while it cleaned its fore tarsi and proboscis; the middle legs meanwhile were outstretched. This specimen remained thus for about four minutes.
Helophilus trilineatus. (Plate XXIX, fig. 5.)
Not very common. I captured one specimen at Taieri Mouth in January (1908) as it alighted on a blade of grass in the sun. At Roslyn, during February of the same year, two were obtained resting on a marigold-flower exposed to the sun.
Found at Roslyn, November (1908). I captured this species amongst some long grass in the sun, the day being very warm. A large number were observed hovering over a stream on Mount Cargill during February
[Footnote] * I have lately observed a distinct difference between the flight of S. novœ-zealandiœ and that of M. fasciatum: the movement of the former being jerky contrasted with the gliding motion of the latter.
(1909), and in the same month, as well as in March, several were captured on the hills of Purakanui. H. antipodus produces, during flight, a humming sound like that of a bee, but of a more acute tone.
Common at Roslyn during February and March (1909). One very hot and sunny day in January I captured this fly on the banks of a small stream above Murdering Beach.
There is no record of this fly having been found before in New Zealand, since Captain Hutton's specimens were captured at the Chatham Islands. I found an individual on the sea-shore of Taieri Mouth, where it had been blown by a strong wind, in January (1908), and the following month I captured another hovering above a clump of marigold-flowers at Roslyn. On a small cliff at Tomahawk, during October (1908), a large number were taken while at rest on or hovering over some wild flowers attached to the rock; at the foot of this cliff a stream runs into the sea.
Captured on a hillside near the bush at Taieri Mouth, December (1907). Two specimens were obtained at Roslyn during September (1908), and two more from Tomahawk in the following month.
Syrphus novæ-zealandiæ. (Plate XXIX, fig. 1.)
One of the most abundant of New Zealand Syrphids: it is to be found everywhere during the season, appearing about September and becoming less common in April; only a few are to be seen during May, and then only in sunny weather. This species varies greatly in colour, the yellow being in some a deep in others a very light shade, and may even be tinged with green. If a specimen be captured shortly after it has emerged from the pupa, the yellow spots are transparent, the black colour transmits the light, and thus the organs contained in the abdomen are rendered visible. I kept two specimens in confinement—a male and a female—for a few days. The male flew about more than the female, the latter feeding, most of the time, on the pollen of daisies which I had put in for food. These observations were made during May (1909), at which period the weather was becoming cold, so that the Syrphids were inert; but on the application of a little warmth they immediately showed signs of returning animation—the female returned to the flowers, while the male amused itself by endeavouring to find an exit. After a few minutes the female would stop feeding and stretch out the proboscis to its full length; this action having been accomplished once or twice, feeding was resumed; occasionally the fly would rub the proboscis with the fore tarsi. When this species alights, the wings are either held outstretched or folded over the abdomen, which is frequently kept in motion, as in E. tenax. On a drop of nitric acid being held about a quarter of an inch from the antennæ of a female, the fly immediately started back or dodged from side to side, endeavouring to avoid the acid; when held at the side of the thorax the acid did not appear to affect the specimen.
Syrphus ortas. (Plate XXIX, fig. 2.)
This species is rare. I have found only one specimen, which was resting on a dandelion exposed to the sun—Roslyn, September (1908).
Melanostoma fasciatum. (Plate XXIX, fig. 3.)
Common; usually to be observed from January to April. I found no specimens at Taieri Mouth at the beginning of 1907, but they were abundant at and round about Dunedin during January 1908. A large number were captured amongst long grass and upon rushes growing in swamp exposed to the sun.
Series C Y C L O R R H A P H A S C H I Z O P H O R A.
Division 1.—Muscidæ Calyptratæ
Gasterophilus hæmorrhoidalis (Bot-fly, introduced).
During February (1909) I observed a large swarm hovering about a young horse, attacking the animal at the knees and sides, and, as they flew about the place upon which they wished to alight, they would suddenly dart in and out, each time coming into contact with the horse's flesh.
This is an extensive family, the members varying more or less in size; they abound in various situations, some in barren localities, others upon the inflorescences and leaves of plants; they are parasitic, at certain stages of development, upon the larvæ of other insects, thus being invaluable factors in the destruction of injurious species.
Not common. This species was captured on a hillside near the bush at Taieri Mouth one very sunny day in December (1907).
A single specimen was captured amongst long grass in the evening, at Roslyn, February (1909), and another on the sandhills at Ocean Beach during May of the same year.
Very common on the tree-trunks of the bush at Taieri Mouth, December (1907), but I only found a single specimen on a flax-leaf at Tomahawk, October (1908).
Captured in large numbers, together with the preceding, at Taieri Mouth, December (1907). I obtained another specimen at Mount Cargill, February (1909).
Not common. I have only a single specimen, which was captured on Mount Cargill during February (1909).
Not common. Specimens captured during December (1908) at Barewood, Central Otago.
Common. Captured on a red rata bush at Roslyn, September (1908), and on a laurel hedge during May (1909).
Phorocera tecta. (Hutton, Trans. N.Z. Inst., vol. xxxvi, p. 151.)
Common at Barewood, Central Otago, during December (1908).
I have only obtained a single specimen of this species, which was captured by sweeping the net through long grass at Roslyn, February (1909).
Fam. Sarcophagidæ (Flesh-flies).
The members of this family are to be found upon decaying animal and vegetable matter.
Sarcophaga impatiens. (Plate XXVIII, fig. 2.)
This common fly is found in most situations. During December (1907), at Taieri Mouth, I captured a specimen near a swamp. About the middle of June (1908) I picked up another individual which was lying on the Tomahawk sea-beach, and several were obtained from the swamp behind Murdering Beach during January (1909), as well as from Long Beach during the two following months of the same year.
Fam. Muscidæ (House-flies; Blow-flies).
Lucilia cæsar (Green Bottle-fly, introduced).
Abundant everywhere, living upon decaying animal matter.
Calliphora erythrocephala (introduced Blow-fly).
Abounds in all situations.
The common New Zealand blow-fly. Abundant throughtout the season from about September onwards.
Common. During October (1908) I captured a large number on Ocean Beach. On stirring up the heaps of dried seaweed which lay about the sand above high-water mark I was surprised by the large numbers of this species which emerged, together with numerous semi-transparent flies. By examining the latter I found that they were specimens of C. hortona which had evidently just completed pupation. When first obsrved, the wings were crumpled or folded up longitudinally along the margin of the dorsal surface of the abdomen. At this stage the whole body was greyish in colour, and the abdomen, when held to the light, was seen to be semitransparent. After about three hours the coloration of the mature fly began to develop: the abdomen became opaque and assumed the final blue tint, the thorax became gradually darker, the bristles took on their permanent colour, and the wings unfolded, the whole fly becoming transformed in colour. Before this transformation commenced, the ptilinum projected considerably, but was gradually withdrawn as the fly became mature. The wings of this species presented a peculiar appearance immediately after they had unfolded: two cross veins, connecting the first and second longitudinal veins, were absorbed as maturity approached. I have observed this structure in the wings of other genera.
This species is common throughout the season.
Evidently rare. I have captured three specimens in all—one at Ocean Beach, October (1908); a second on the beach at the Nuggets a few days later; and a third at Barewood, Central Otago, December (1908).
Found in most localities during the season, common.
Not uncommon. I captured a number at Roslyn during September (1908 and 1909); also in May and October (1908).
I captured a single specimen on a very warm day at Roslyn, February (1909).
Three specimens were captured at Purakanui during January (1909), and two others at Dunedin in the following month.
I captured one specimen during a very sunny day, at Roslyn, November (1908); two more were obtained from Mount Cargill, also during a sunny day in Febrauary (1909).
Abundant. Found in a swamp at the Nuggets, October (1908), and captured in a swamp behind the sea-beach of Murdering Bay during January and February (1909).
Not very common. In October (1908) four specimens were obtained from a swamp at the Nuggets, and only one from among rushes, Purakanui, February (1909).
Two specimens were captured in a swamp at the Nuggets, October (1908).
Trichophthicus villosus. (Hutton, Trans. N.Z. Inst., vol. xxxiv, p. 171.)
Abundant. This fly is recorded from the Auckland Islands, but not from New Zealand, by Captain Hutton. Taken in large numbers from a swampy locality at Purakanui, January (1909).
Limnophora rapax. (Plate XXVIII, fig. 3.)
Common during December (1908) and January (1909) at Roslyn, and on the banks of a stream on Mount Cargill.
A common house-fly, which is introduced.
Not common. Two specimens were captured on Mount Cargill, February (1909).
This species was common on sandhills and patches of dried kelp during October (1908) at the Nuggets, and less common at Ocean Beach, March (1909).
Division II.—Muscidæ Acalyptratæ.
Not common. Found on sea-beaches during the whole year, several being captured near the mud-flats at the head of Otago Harbour in the middle of winter (1909). If examined microscopically, the contents of the stomach are found to be composed of various portions of algæ, upon which the fly evidently feeds. This species is not very rapid in flight, and, since it only flies for a short distance near the ground, it can easily be run down; when on water it rests with the wings incumbent, and supports itself by placing the five tarsal joints along the surface. Being aquatic, this fly runs more rapidly on water than on land. If it happens to alight on its back, it wriggles about on the distal extremities of the long femora until it rights itself. The habits of this species are, generally speaking, sluggish.
Common. Several specimens were captured on a window at the Nuggets during October (1908), and in the bush of the same locality; others were found in a swamp behind Murdering Beach, January (1909), and at Roslyn in February of the same year.
Common. Has been previously captured at the Chatham Islands, but not in New Zealand. Found in the same localities as C. monstruosa, and resembles that species in being aquatic as well as in its mode of flight. It burrows in the sand under the heaps of dried seaweed. This fly did not suffer from being placed in a jar of water which I kept agitated, and from which the specimen flew when the water was allowed to become smooth. I held another specimen under water for a short time (a minute and a quarter), but when released it rose to the surface, ran about for a few seconds, and flew away. This species is buoyed up by the numerous globules of air which adhere to the bristles and hairs.
Abundant about Dunedin from November (1908) to February (1909). To be observed resting upon grass, lupin-bushes, and other forms of vegetation.
An aquatic fly abounding on the surface of pools and on the damp banks of streams on the sea-shore. From my observations, they are to be found from January to May (1909). The larvæ live in saline pools on the sea-shore, and have been described by Dr. Benham in the Trans. N.Z. Inst., vol. xxxvii, p. 308.
A minute fly about 2 mm. in length. This species is not common, only two specimens having been obtained, during August and September (1908).
Fig. 1. Odontomyia chloris.
Fig. 2. Sarcophaga impatiens.
Fig. 3. Limnophora rapax.
Fig. 1. Syrphus novœ-zealandiœ.
Fig. 2. Abdomen of Syrphus ortas.
Fig. 3. Abdomen of Melanostoma fasciatum.
Fig. 4. Saropogon fugiens.
Fig. 5. Helophilus trilineatus.
Fig. 6. Itamus varius.