THE SYRPHIDAE OF OHIO 25 



generations occur in a year and become to some extent confused, the date 

 of the appearance of young can not be stated in a general way for all spe- 

 cies. Some of the aphidophagous species, whose stages have been worked 

 out, were studied only^ in the autumn generation. The larvae of this 

 generation occur quite generally in the latitude of Ohio from the middle 

 of September to the middle of November, or even later, depending on 

 the season. Some species were found, as larvae, as early as the first of 

 May, and others very commonly during June. Larvae of certain species 

 seem most abundant during June, July and August. 



Duration in the larval stage in those species for which I have records 

 varies from one to three weeks and seems to be determined in part b\- the 

 amount of food at hand. 



Wheeler states that young larvae of Microdon tristis may be found in 

 the nest during July; that these mature by autumn and after passing the 

 winter in the ant nest, pupate in April or May. There is, in his opinion, 

 only one annual brood in temperate regions, the adults emerging in June. 

 The larva of Mesogramma polita is said by Ashmead to mature in from 

 eight to ten da3's. 



Those species which as larvae are predaceous, are to be looked for 

 wherever small soft-bodied Homoptera, especially Aphididac, occur in col- 

 onies. They are to be found alike on trees, shrubs, herbaceous plants, 

 weeds, field-crops and garden-crops. The phytophagous species have been 

 found on corn, working either between the base of the leaf and the stem 

 or on the tassels. The larvae of Microdon live in the nests of ants, 

 wasps, or termites, either in the soil, under stones, in decaying logs or 

 in cavities in or under the bark of trees. In the United States the most 

 frequent hosts are probabl}' species of Formica. 



Species of Eristalis were found abundantlj'in evaporating vats at the 

 Columbus sewage-disposal plant where sewage in an advanced state of 

 decay is left exposed for some time. They are to be found in all sorts 

 of foul or stagnant pools, in organic debris, excrement, ooze about drains, 

 in watering troughs, etc. Other "rat-tailed" species, e. g. Mallota sp., are 

 said to live in decaying wood or trees. 



The habitat of others may be noted from the outline of larval habits 

 given below, p. ^yi, and ranges from various positions on or within living 

 plants, including bulbs, cacti, and fungi, thru decaying wood or exuding 

 sap, decaying vegetable matter, manure, and soft mud impregnated with 

 decaying organic material, to a strictly aquatic condition in stagnant or 

 foul water. Another line of specialization from the same original habitat 

 has taken up the predaceous habit; certain specializations from this have 



