Sarcophaga carnaria is another species which occasionally infests human sores, and which enters houses in search of filth or carrion on which to lay its eggs; it is viviparous and produces not eggs but live larvae. One female can give birth to 20,000 young; and Redi states that the larvae of these flesh-flies will in twenty-four hours devour so much food and grow so quickly that they increase their weight two-hundredfold.
Finally, there is a group of flies whose larvae penetrate under the skin of human beings and give rise to definite subcutaneous troubles. But, fortunately, these are, with few exceptions, confined to the warmer regions of the earth, and there is very little risk of their causing real trouble in Northern or Central Europe.
Fig. 28.—Side view of blow-fly (Calliphora erythrocephala) (× 5). A, Cheek (jowl); B, squama; C, halter. (From Graham-Smith.)
The troubles or diseases caused by the presence of fly larvae in the body are grouped in medical language under the term ‘myiasis,’ which Graham-Smith defines as follows:—
‘The term myiasis signifies the presence of dipterous larvae in the living body (whether of man or animals), as well as the disorders (whether accompanied or not by the destruction of tissue) caused thereby. Though not strictly coming within this definition, the sucking of blood by larvae through punctures of the skin, which they themselves produce, may be included for the sake of convenience in classification.
Myiasis in man may be produced by dipterous larvae:—
(a) Sucking blood through punctures in the skin (Auchmeromyia luteola).
(b) Deposited in natural cavities of the body (Chrysomyia, Lucilia, Sarcophaga, Calliphora, Oestrus).
(c) Deposited in neglected wounds (Chrysomyia, Lucilia, Sarcophaga, Calliphora).