ECOLOGY OP ISLE ROYALE. 67 



mvariably in locations so bounded by rocks or shore that the waves 

 strike them always in one direction. An instance of this was seen 

 near the light-house. A small inlet about 5 m. in length and width 

 opened towards an island. Waves struck it in two directions, both 

 ■diagonally, but rebounding from the rocks continued into the inlet in 

 one direction. At its back was a small but typical beach, the only one 

 in the immediate vicinity and likewise the only spot where the waves 

 always came in the same direction. As a consequence of this directive 

 action the beaches always lie at right angles to the direction of wave 

 action. 



The gravel of which they are composed varies in size from fragments 

 as large as one's flst to mere sand, but the biota of the sand beaches 

 is so diffei-ent that it requires separate discussion. There is no vege- 

 tation, but the beaches are frequently strewn with dry drift wood in 

 which several kinds of fruits, dead insects and shells may be found. 

 The gravel is dry on top, but is always moist at a depth of one or two 

 decimeters or even less. The broader beaches have full exposure to 

 ithe sun, but the narrower are shaded, and all are bounded at the rear 

 by a narrow but dense zone of alder. 



The fauna of these beaches is limited in species, probably owing to 

 ■the lack of food, although the number of individuals is relatively large. 



Caddice flies are rather common running about over the finer gravel 

 just above the reach of the waves, or sometimes taking short flights 

 (No. 10). Stoneflies are associated with them; they crawl about 

 actively over the wet gravel near the water's edge and do not attempt 

 to fly. They are frequently struck by waves which merely wash them 

 a little farther up the bank. A few species of ants are also common, 

 running over and through the gravel (No. 38). They prey on dead 

 caddice flies or even on live ones when they succeed in capturing them. 

 The most characteristic group, however, consists of several species of 

 spiders, which fire found in great abundance on the coarser gravel in 

 the sun (Nos. 16, 25, 38, 39, 60), Lyco^a pratensis Emer., Pardosa 

 lapidicina Emer., Pardosa groenlandioa Thor., Eho latkhorax Keys. 

 They run Avith great rapidity and at the least alarm crawl under the 

 rocks, where it is almost impossible to find them. After the first alarm 

 they usually show themselves in 10 to 15 seconds, but being frightened 

 again, they crawl for some distance under the gravel and are lost 

 permanently. Many of them carry egg cases, and if forced to drop them 

 they spin a web which they follow back in a short time. These spiders 

 are very numerous, probably 10 or 12 to every square metre over all 

 "the gravel beaches. 



Other insects observed were, a small beetle (38) crawling over the 

 ■sandiest part of the beach; two species of small beetles (89) crawling 

 through the coarse sand and fine gravel at the water's edge; a click 

 "beetle, Gorynibites medianus Germ. (41) crawling over sand in a shaded 

 place near a rock cliff; a Scarabaeid, Serica vespertina Gill. (43) ; a 

 heetle, Macropogon rufipes Horn (60). Some fish worms (40) were 

 also found buried 3 dm. deep in moist coarse sand under the gravel 

 "beach in front of the light-house. They were above the level of the 

 -ground water. Butterflies and wasps, which were so abundant on the 



