16 The Animal Ecology of the Cold Spring Sand Spit 



the sand spit to about two-thirds of the way toward its eastern point. Then pugilator 

 abruptly comes in. For a distance of a meter or so the two species occupy ground 

 in common, and, so far as I could make out, peacefully. The pugnax alone occurs at 

 the head of the inner harbor. It burrows in the banks at a level that is reached only 

 by the high tides. Walking along the beach at high tide July 7, I found that many 

 of the fiddlers had migrated to above the high-tide level. It is clear, I think, that 

 they do not find submergence altogether agreeable, and it is probable that prolonged 

 submergence would drown them as it does Ocypoda arenaria, the sand crab of the 

 beaches south of Cape May. G. pugnax prefers the marshier ground and the higher 

 water, and it is probably that preference which determines its spacial separation from 

 pugilator on the sand spit. 



D. THE TOP OF THE SAND SPIT (TERRESTRIAL BORDER ZONE) 



Above the storm bluff on the outer beach, and at a less well-defined line on 

 the inner beach, lies the zone of permanent vegetation in which certain shrubs 

 have gained a foothold. Here the fauna at once assumes a strictly terres- 

 trial aspect. No close ally, even, of a marine form occurs. On the contrary, 

 the animals living on vegetation are precisely those species that occur in the 

 fields, especially the plant feeders: the plant lice (Aphidse), the leaf beetles (Chry- 

 somelidse), the bright-colored Buprestidse, and the various blister beetles. On the 

 sandy ground are sand-colored grasshoppers, sand-colored spiders, Lycosa cinerea, and 

 also small black spiders (Lycosa communis; of. Emerton, 1885), black crickets, and little 

 red ants apparently identical with species that people the upper beach. Over the vege- 

 tation wandered, in early July, an abundance of the predaceous dragon-flies, a black 

 wasp (Polistes), and an occasional dusk-flying butterfly (Hesperidse) — quite the fauna 

 of a meadow not far from water. 



SUMMARY ON THE ANIMAL ECOLOGY OF COLD SPRING BEACH 



The outer beach is a region of breakers where debris is thrown on the shore. 

 The submerged zone is crowded with marine animals, some of which make their 

 way out of the water and others of which contribute the debris with which the upper 

 beach is strewn. The lower beach is covered with Collembola that feed upon micro- 

 scopic organic debris and crawl into the sand at high tide. The line of debris is a 

 rich feeding-ground for animals that live on vegetable matter and on carrion. The 

 debris feeders — Amphipoda, staphylinids, earthworms, ants, carrion flies, necrophorous 

 beetles, attract a predaceous fauna of spiders, robber flies, and tiger beetles. These 

 predaceous species are fed upon, in turn, by the swallows. 



The tip of the beach, where the marsh grass grows, is a region of swift currents 

 which the lamellibranchs (mussels) find advantageous because of the food that the cur- 

 rents bring. The currents tend to wear away the spit, but the mussels grow so abundantly 

 on the banks of the channels as in turn to protect these banks from further erosion. 



170 



