THE EVOLUTION OF ANIMAL COMMUNITIES 77 



only sand but also animals of many different 

 sorts. If the storm is severe a great collection of 

 shells of small lake snails or finger-nail clams may 

 be cast up together with an occasional crayfish 

 and many small and some larger fishes. In spring 

 and summer countless insects will be found in the 

 same drift line with these water-dwelling animals. 

 Normally these insects live in the trees or grass- 

 lands along the lake, from whence they were 

 caught up by a land breeze and carried out over 

 the water into which they dropped when ex- 

 hausted. They were then cast up by the onshore 

 drive of the waves. With them may be fragments 

 of birds and at times an occasional larger animal. 

 I have seen in this drift line a collection of beetles 

 that extended for miles in a row, from one to three 

 feet wide and with hundreds of beetles to the square 

 foot. At the time of the fall migration of monarch 

 butterflies, I have seen similarly a brownish 

 tinge in this drift line that could be distinguished a 

 quarter of a mile ahead caused by the brownish 

 color of the cast-up butterflies. This insect drift 

 furnishes season after season and year after year a 

 fair sample of the insects that are flying on the 

 nearby communities. 



Some of the animals of the drift have survived 

 their watery immersion and are still alive; others 

 are dead. Not all of the animals in this drift 



