THE SYRPHID FLY, MESOGRAMMA MARGINATA, AND 

 THE FLOWERS OF APOCYNUM.* 



Raymond C. Osburn. 



The flowers of the various species of the dogbane, Apocynum 

 spp., have long been known to catch some of the weaker sorts 

 of insects attracted by them, but as far as I am aware, no such 

 wholesale slaughter of a particular species as that herein 

 described has been noted. In fact, if I may judge by the con- 

 versations which I have held with both botanists and entomol- 

 ogists, the capacity of the dogbane for trapping insects has 

 pretty generally escaped notice. 



My own attention was drawn to the subject last summer 

 when Miss Edith Weston, a young student of botany at the 

 Ohio State University Lake Laboratory at Put-in-Bay, brought 

 in some flowers of Apocynum androscBmifolium and called my 

 attention to the fact that the flowers had "bugs" in them. A 

 glance at the flowers showed that there were insects in nearly 

 all of them and that these were all of one species, the common 

 little Syrphid fly, Mesogramma marginata (Say). Many of these 

 were still alive, though evidently held in such a manner that 

 they could not escape. As the flowers are open bells, my 

 curiosity was aroused and I began a careful examination. 



Having in mind the related milkweed, Asdepias, whose 

 flower clusters sometimes entangle the legs of insects by a 

 sticky secretion, I was a little surprised to find that all of the 

 flies in the Apocynum flowers were held by the proboscis. As 

 many as four were present in some of the flowers, the little bell 

 being as full as it would hold. Frequently the flies appeared to 

 have made their escape by pulling off the terminal portion of 

 the proboscis, and many of these parts were found in the 

 flowers. Less frequently they had pulled off their heads in their 

 struggles. In either case it would seem that the flies must 

 ^'permanently vitiate their future careers" just as certainly as 

 if they remained held. 



In order to obtain some estimate of the number of flies 

 caught, a hundred of the flowers were examined. These were 

 taken just as they came on various flower clusters, and all were 



*Contribution No. 61, Department of Zoology and Entomology, Ohio State 

 University, Columbus. 



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