C) CONXECTICUT GEOL. AND NAT. HTST. SITKVEY fBull. 



females. In some species the eyes of the males touch, a condition 

 known as holoptic, while the eyes of the female remain separated, a 

 dichoptic condition. This ditference is not always found, for the 

 eyes of both sexes may be widely sepai-ated m some species and may 

 touch in others. The extreme of sexual dimorphism in wing structure 

 is reached among flies of which the female sex is wingless and the 

 males winged, as some Phoridae. The wings of the males of some 

 mosquitoes are smaller and narrower than those of the females of 

 the same species. 



Flies are of great economic importance to the people of Con- 

 necticut, not being exceeded in this respect by any other grou}) of 

 insects. They are both deleterious and useful. Aside from their role 

 in the mechanical and CTclical transmission of diseases of man and as 

 irritating nuisances, tliey directly affect nuui's economy in several 

 ways. It is not possible to go into great detail in the nuitter here, 

 so a few illustrations will have to suffice. 



Several species are of more or less value to man. The larvae 

 of many aquatic crane-flies and midges serA^e as food for small Hsh. 

 Adult syrphids pollinate flowers. Many species of muscoid flies feed 

 on dead and decaying organic matter and can be considered useful 

 in disj^osing of this material. The larvae of a great many flies are 

 parasitic on other insects, and larvae or adults, or both, of other 

 species are predaceous on insects. Whether or not such species are 

 usef id to man depends on what they attack. If the prey is deleterious 

 to man, the parasite or predator ma}^ usually be considered beneficial, 

 liobber-flies (Asilidae) are predaceous in both adult and larval stages, 

 the adults capturing other insects, sometimes honey bees, on tiie 

 wing and the larvae seeking their prey in the soil. The larvae of 

 bee-flies (Boudndiidae) are parasitic (m bees, wasps, grasshoppers, 

 etc., and cyrtid larvae parasitize spiders. Adult dolichopodids capture | 

 and eat smaller insects, and larvae of many Syrphidae prey uj^on 

 aphids. Our white grubs are parasitized by the larvae of the Pyrgo- i 

 tidae. The most important and best known family of parasitic flies 

 is the Tachinidae. Their larvae live in the larvae or adults of nuuiy 

 otlier species of insects, and some are very valuable in reducino- the 

 abundance of certain pests. Some tachinids attack a large number of 

 different insects, and others are very restricted in their host relation- 

 ships. One species commonly found in Connecticut. Compsilnra con- 

 cinnafa, was brought to the' United States from Europe to combat 

 tlie gypsy moth. It attacks a number of different species of cater- 

 l)ij]ars. The very connnon little reddish tachinid. Trkhopoda pm- 

 nipe^-, confines itself mainly to the common squash bug. The army 

 worm is lieavily parasitized by flies of this family, and during an 

 army woruj (nitbreak, fly eggs can be seen on a large proportion of 

 the catei-pillai's. 



The use of flies in purely scientific investigations should be 

 mentioned. The little red-eyed* vinegar fly. Drosophila. is probably 

 the most famous animal known to geneticists and has been the source 

 of more information on hei-edity than any other species of aninud. 



