204 
If, as has already been referred to, Phora cleghorni is truly para, 
sitic on the Silkworm Tachiuid of India (Trycolyga bombycis), this would 
add another parasitic family to the Diptera, the Phoridae. Moreover, 
it would mark a very striking deviation in the parasitism of the order. 
Four genera of Phoridae are known in North America. The larvae 
usually feed on dead snails, insects, and fungi, or are necrophagous. , 
Eeviewing these families, we find that only two out of the seventeen 
can be classed as actually injurious. The Acroceridae ape parasitic on 
spiders, which latter are on the whole beneficial insects. The second 
family, the Oestridae, are highly injurious. 
The Conopidae and Bombyliidae, in so far as they destroy wild bees, 
including the humble bees, might be considered somewhat injurious, 
from the fact that the humble bees are of use in the fertilization of 
certain flowers, notably red clover. These two families contain about 
the only known dipterous parasites of bees. Four families are only 
partly parasitic in their habits. They are the Cecidomyiidae, Sarco- 
phagidae, Muscidae, and Anthomyiidae. Such members of them as are 
parasitic destroy injurious insects. 
The remaining families, the Conopidae and Bombyliidae being included - 
are practically without exception parasitic or injurious insects, if we 
may include the Dexiidae, which accidentally and rarely diverge from 
these habits. These make eleven families, the genera in which sum up 
more than 225 in North America. Four or five species to each genus 
is a low estimate, making fully 1,000 North American species. It 
should be noted that these flies are practically without enemies, and 
therefore increase rapidly. This accounts for their great abundance, 
both in individuals and species, especially in the Tachinidae. It can 
readily be imagined, therefore, that their agency in the destruction of 
injurious insects is of paramount importance. 
