132 NATURE SKETCHES IN TEMPERATE AMERICA 



be modified after the many biological interests that centre 

 here have once been awakened. Muller found that a number 

 of insects were instrumental in cross-fertilizing this species 

 of plant in Europe. Among them were the honey bee and 

 bumblebee, besides other species of bees, wasps, and Syrphus 

 flies. He says: "From my own observations it is clear that the 

 small pollen-feeding bees (Prosopis) and Syrphidae are very 

 frequently the fertilizers of this genus (Verbascium)." 



Similarly, our forms play an important part in cross-fertiliza- 

 tion of this plant, as well as others. The body vestiture of 

 many of the Syrphus flies is composed of bra,nched and spiculate 

 hairs which gather pollen. Some of the Syrphus flies mimic the 

 bumblebees and wasps, while others resemble the honey bee. 

 In the colored photographic plate illustration is pictured one 

 of these insects resting on the flower of a purple aster. It is 

 known as the drone fly, Eristalis tenax. This insect's resem- 

 blance to a male honey bee is so perfect that inexperienced 

 observers often mistake it for the real bee. In the late fall 

 of the year, after the first frost, it becomes very sluggish, and 

 many of them, benumbed by the cold, appear on sidewalks 

 and sides of buildings. The larva of this insect is the well- 

 known "rat- tail" form, which is sometimes found in hollow 

 tree stumps where the rain water has stood for a long period. 

 Here the larva living in the stagnant water is provided with a 

 long, projecting, tail-like structure, at the end of which a 

 number of spiracles occur, through which it can breathe the 

 air when thrust above the surface. 



On the same plant of the purple aster is shown the moth, 

 Plusia simylex, as an associated guest. It is one of the night 

 flying moths, but they are sometimes found on cloudy days 

 visiting flowers in the afternoon. The forewings are marked 

 by a pair of silvery spots; these spots, together with the rich 

 brown coloring on the forewings, simulates the ground upon 

 which they often rest during the day. 



In another chapter is mentioned the aerial performances 

 of the Tabanid flies. These insects obtain their nourishment 

 principally by sucking the blood of animals, but the Syrphus 

 flies are almost always flower frequenters. From these facts, 

 and other interesting features gleaned from their life histories. 



