May, 1920] The Syrphid Fly and Apocynum 263 



manently held. Prof. M. E. Stickney, of Denison University, 

 confirmed this observation and we repeated it together a 

 number of times. 



The proper explanation appears to be that the flies are not 

 held until the proboscis becomes sufficiently gummed-up with 

 the sticky secretion. Larger insects appeared to have but little 

 trouble, though in one case a drone fly {Eristalis tenax) was 

 caught, by the proboscis, between the anthers. This is a robust, 

 active fly a half inch or more in length. 



The patch of Apocynum plants, on which these observations 

 were made, was some sixty feet long by five or six feet in width. 

 There were many thousands of the flowers and, if the 100 

 carefully examined form a sufficient basis for an estimate, there 

 must have been at least as many of the flies caught as there 

 were flowers. A careful survey of the flowers in the patch indi- 

 cates that this estimate is not far from wrong. 



Mesogramma marginata is a common little fly, 5 to 6 mm. 

 long, but one seldom sees in it in such numbers. Its habits 

 seem to indicate that in the larval stage it feeds on aphids, like 

 many other Syrphid larvae, and thus it is a beneficial insect. 

 This being the case, the dogbane is a detrimental plant in 

 regions where aphids do any damage. 



Insects Caught. — Aside from the Mesogramma, other 

 insects appeared to visit the flowers without difficulty, though 

 a few individuals of other species were caught. The list of 

 those captured, as observed in several hours collecting at the 

 patch on different occasions, is as follows: Mesogramma mar- 

 ginata, many thousands; Eristalis tenax, one; one small 

 Tachinid; one small Muscid; and one small Tineid moth. 



Insects Not Caught. — On each visit to the Apocynum 

 patch, observations were made as to what were the regular 

 visitors, and a collection was made of all the insects seen to 

 enter the flowers. Insects were swarming about the flowers 

 and most of the following list of 25 species were common: 

 Eristalis tenax, Syrphus americanus, Sphcerophoria cylindrica, 

 Syritta pipiens, Lim?iophora narona, Peleteria robusta, Pseudo- 

 pyrella cornicina. Anthrax alternata, Bombylius fulvibasis, Sto- 

 moxys calcitrans, Sarcophaga melampyga, Lygceus kalmii, Formica 

 fusca siibsericea, Apis mellifera, Megachile latimanus, M. brevis, 

 HylcEiis modestus, Heriades barbatus, Halictus sp., Basilarchia 



