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(7) Oestridce. — None of these flies attack insects or any invertebrates, 
but are without exception parasitic on mammals. They are of much 
economic importance, but unlike the other families of parasitic Diptera, 
they are highly injurious on account of the hosts which they infest. 
Nearly all of our domestic animals, and man himself, are liable to their 
attack. Seven North American genera are known. 
(8) Phasiidce. — Seven North American genera are known. All are 
parasitic, without known exception, on Orthoptera, Hemiptera, and 
Coleoptera (locusts, Pentatomids, Coreids, and a beetle). 
(9) Gymnosomatidce. — Two genera occur in North America. They are 
parasitic on Hemiptera and Lepidoptera. The species attack Penta- 
tomids, and Oistogaster has been bred from Leucania. 
(10) Ocypteridce. — Seven genera are known in North America. They 
are parasitic, so far as known, on Orthoptera, Hemiptera, Coleoptera, 
and Lepidoptera (locusts, Pentatoma, Cassida, Leucania). 
(11) Phaniidce. — Two North American genera occur. So far, they 
have been found parasitic only on Coleoptera. 
(12) TachinidcB s. str. — Over one hundred and twenty genera are 
known in North America. These, without any known exception, are all 
parasitic on insects of the orders Orthoptera, Coleoptera, Lepidoptera, 
Hymenoptera, but more particularly on Lepidopterous larvae. This 
family is preeminently parasitic on Lepidopterous larvae. Hundreds of 
species exist, which destroy immense numbers of them annually. The 
Tachinidae, from this fact, are perhaps the most important group of 
beneficial insects which exists. 
(13) Dexiidce. — Over forty North America genera are known. These 
are parasitic, so far as recorded, on Orthoptera, Coleoptera, and Lepi- 
doptera. A Dexiid has also been bred from a scorpion, and from snails. 
(14) Sarcophagidce. — About seven genera are known in North America. 
The Sarcophagids are largely creophagous, and also coprophagous, but 
some species are occasionally parasitic on Orthoptera, Coleoptera, and 
Lepidoptera. Phrissopoda has been bred from Lepidopterous larvae, 
and from snails. Sarcophaga has been bred from all three orders. 
Sarcophaga has likewise been bred from snails, and a species is also 
parasitic beneath the skin of turtles. 
(15) Muscidce s. str. — About sixteen North American genera are 
known. These flies are largely coprophagous and creophagous, but 
some species have been bred from lepidopterous larvae. A Lucilia has 
been found parasitic on toads. 
(16) Anthomyiidce. — Twenty-one North American genera occur. Some 
species are occasionally parasitic on Orthoptera, and some other insects. 
(17) Ochthiphilidce. — So far as known, these acalyptrate Muscids, 
of which there are two genera in North America (one introduced from 
Australia) are parasitic on Aphids and Coccids. It is noteworthy that 
the Cecidomyiidae and this family furnish the only parasites of Aphids 
and Coccids among the Diptera. 
