Simulia australiensis (Plate [VI]., fig. 1, 1a larva, 1b pupa).
Every one knows the sandfly, the little black insect that so persistently perches on our hands and faces and inflicts its painful punctures, which in many cases are followed by large swellings, often lasting for several days and causing much irritation. Its larva (Fig. 1a) inhabits clear running water, climbing about in strong currents by means of a pair of suckers situated at each end of the body, two being placed on the prothoracic segment just behind the head and two others close to the anal extremity. These the insect employs rather curiously, the anterior pair being first affixed and the others drawn up close behind them, its elongate body consequently forming a loop. Clinging by the posterior suckers for a moment the larva then reaches forward, re-affixes the anterior ones, and draws up the posterior as before. Breathing is performed by two spiracles situated on the last abdominal segments near the hind pair of suckers. Two large air-tubes originate from these and run forwards, giving off branches to all parts of the body; they terminate in a number of air-sacs in the thorax. The food of this larva consists of animalculæ, which are no doubt obtained by drawing the two ciliated appendages rapidly through the water several times in succession, their contents being afterwards gathered up by the smaller organs and passed into the mouth. When about to assume the pupa state the insect covers itself with a glutinous envelope, which is firmly joined to the under side of a leaf, the transformation taking place within a few days. The pupa can hardly be distinguished from a small moth chrysalis except for a pair of branching filaments, which arise from the top of the thorax and serve the purpose of gills (Fig. 1b). Before emergence the anterior segments are projected nearly out of the cocoon from which the perfect sandfly makes its escape, and floating to the surface of the water ascends the stem of an aquatic plant to expand its wings. I should here remark that as with the mosquitoes, the bloodthirsty propensities of the present species have no doubt been acquired since the arrival of man and other warm-blooded animals.
Group Brachocera.
Family Tabanidæ.
Tabanus impar (Plate [VI]., fig. 6).
I have figured this fine species as a representative of a most important family of Dipterous insects, but am at present quite unacquainted with its life-history. It occurs plentifully on the margins of the forest throughout the summer.
Family Bombylidæ.
Comptosia bicolor (Plate [VI]., fig. 2).
This conspicuous species is very abundant in glades throughout the summer, flying with great rapidity, and delighting to suck honey from the numerous shrubs which are in blossom at that time of year. It is a social species, and is usually found in companies of fifteen or twenty individuals, which engage in endless dances, two insects often seizing one another on the wing and then revolving together like a wheel in rapid motion. Their manœuvres in avoiding the strong gusty wind, so often prevalent in early summer, are also interesting; the insects play upon the wing whilst the air is quiet, but if a breeze springs up they instantly settle on the nearest bush, rising to renew their sports when it is again calm. These flies are rather variable in colour, some specimens being dark brown, whilst others are more or less covered with greyish-white hairs; individuals are also often met with quite black and shining, their hirsute covering having been completely rubbed off. The female may be at once recognized by her solid, fleshy abdomen, that of the male being inflated by two great air-bladders, which cause that portion of the body to appear semi-transparent when the insect is held up to the light. The figure (2) is taken from a specimen of the latter sex.
Closely allied to the present insect is Comptosia virida, n.s. (Fig. 3), which can be at once distinguished by its brilliant green eyes and pale grey clothing. The larva of this species is a large white maggot, rather robust, and possessing a small head. It inhabits the dense moss growing on the trunks of trees in the forest, feeding on the roots of these plants, and finally forming an oval cocoon, in which it changes into the pupa shown at Fig. 3b. The perfect insect appears in a few weeks' time, when it may be taken in similar situations to C. bicolor, but in much fewer numbers.