The SIMULIDAE contains a number of small Diptera abundant in Europe and America, where they are known as “Sand-flies,” “Black-flies,” or “Buffalo-gnats”; they swarm in the marshy lands of the Mississippi where Howard says, “They rival the mosquito in their blood-thirsty tendencies, and not only do they attack human-beings, but poultry and domestic animals are frequently killed by them.” We are fortunate in having very few of these pests; only one species was discovered by Skuse, who named it _Simulium furiosum_, and says it is a rare fly only found in the Gosford district N.S. Wales. These flies must not be confounded with the midges known in Australia as “Sand-flies,” which are very different insects belonging to the Genus _Ceratopogon_, of the Family Chironomidae. The BIBIONIDAE are medium sized flies with thickset bodies somewhat hairy; smoky wings; robust legs; short antennae; and three ocelli. The females deposit their eggs in dung or vegetable matter, and the maggots have rows of transverse bristles on the segments; and traces of eyes can be found in the head segment. The perfect flies are sluggish in their movements and are commonly found upon flowers. Twelve species have been described from Australia, of which _Bibio imitator_ is our commonest species; it is very abundant in the early summer upon the flower heads of _Astrotricha floccosa_, which grows in most of the valleys round Sydney; it has a wide range from Tasmania northwards in similar forest country. The male is under ½ an inch in length and is of a uniform black tint, with the thorax dull red; while the larger female is of a uniform reddish brown, and both sexes have the typical dark clouded wings. The South American Genus _Plecia_ is represented by four species, two of which I collected in North Queensland. The North American Genus _Scatopse_, the larvae of which breed in all kinds of decaying matter and in sewers, is represented by two species, of which _Scatopse fenestralis_ is so common about Sydney that Skuse says: “In the spring months it is scarcely possible to find a window without one or two specimens, while I have frequently seen hundreds swarming on the inside of shop windows in the city.” Family 3. Mosquitoes. CULICIDAE. No insect pests are better known or more world wide in their distribution than mosquitoes. As might be expected, they are abundant in tropical countries, yet one would hardly expect them to be much of an annoyance in the temperate regions. Yet in Lapland, and even farther north, they worry the inhabitants and the reindeer all through their brief summer. [Illustration: Plate XXVII.--DIPTERA. Family CULCIIDAE. 1. _Culex fatigens_ (Wiedermann). Larva. 2. _Culex fatigens_ (Wiedermann). ♀. 3. _Culex fatigens_ (Wiedermann). Wing. 4. _Anopheles annulipes_ (Walker). ♀. 5. _Anopheles annulipes_ (Walker). Wing.] [Illustration: _Plate XXVII.--DIPTERA._]