C. B. Davenpokt 13 



here. To test the quickness with which these flies accumulate I took a recently 

 drowned turtle from the water at 3 P. M. July 7, and left it at the edge of the retreat- 

 ing tide. At 4:15 p. m. (wind south) I counted over thirty of the bronze flies upon 

 it. It remains to be determined whether it is chiefly sight or smell that attracts them. 



Underneath the carcasses of the horseshoe crabs one will find also large numbers 

 of the carrion beetle, Necrophorus, and larvaB of the museum pests (Dermestidse). 



The rich fauna of carrion feeders and herbivorous and omnivorous species deter- 

 mines still another fauna, namely, a predaceous one. Thus, running spiders, almost 

 as white as the sand, frequent the upper beach and sometimes pass down to the upper 

 part of the lower beach. These belong to the species Lycosa cinerea — a species that 

 occurs commonly in Europe also, and is by no means confined to the sand of beaches. 

 I have seen them carrying off Orchestia toward the storm bluff. More powerful still 

 are the robber flies (Asilidse) which pounce upon carrion flies. Their path of flight is 

 curved, and at the moment of alighting an offset is taken several centimeters to one 

 side. Altogether the irregular flight seems well adapted to the end of putting the vic- 

 tim off its guard, like the curve in the path of the ball thrown by an expert baseball 

 player. Tiger beetles also occur abundantly on the beach in the bright sunlight, 

 especially in August and September. They are chiefly of the species Cicindela repanda 

 Dej. They are the most rapid fliers among beetles and feed upon the other insects of 

 the beach. Finally, all these insects must fall victim to the swift and powerful swal- 

 lows which course up and down the beach, especially in the latter part of the afternoon. 



On the upper part of the upper beach there occur also a few stragglers from the 

 vegetation-grown top of the sand spit. Here one finds grasshoppers almost as white 

 as the sand. The white color of this species seems partly determined by the color of 

 the background, for placed in a cage on grass these spiders become darker, as experi- 

 ments at the Biological Laboratory have repeatedly shown. Whether the grasshop- 

 pers feed upon the dead vegetation of the tide-line was not ascertained. Crickets, 

 Gryllus abbreviatus, quite as black as those living in the grass, occur scatteringly on the 

 upper beach; and under the waste lumber the sow-bug, Oniscus, which is only half 

 adjusted to a terrestrial existence, finds a living on the water-soaked wood. 



B. THE BEACH ON THE TIP OF THE SAND SPIT 



The tip of the spit is transitional between the inner and the outer sides. Here 

 the sandy beaches of the north side gradually pass over into the mud-flats of the south 

 side with their thick growth of marsh grass, Spartina. Indeed, at the tip of the spit 

 there is a constant struggle going on between the upbuilding tendencies of the Spar- 

 tina, which tends not only to hold the mud in which it grows together, but also to 

 accumulate additional silt, and the scouring away tendencies of the tide that rushes 

 through the gut* Wherever a weak spot appears in the mass of Spartina there a chan- 

 nel becomes gradually worn through (Fig. 6). These channels gradually widen and 

 may anastomose, and thus the Spartina be left on elevated hummocks, which would 



167 



