ECOLOGY OF ISLE ROYALE. 75 



nests may be built at less depth, as one of Formica fusca L. (No. 100) 

 at a depth of 4 cm. These loose rocks tend to conserve the moisture 

 just as do the crevices. 



Beetle lai-vae are rarely found, owing to the abundance of ants which 

 feed upon them. TTiey occur under rocks or in the deepest soil deposits 

 where the moisture is conserved. (Nos. 80, 82, 102.) No. 102 contains 

 two species of larvae, one a Cistelid, the other Drasterius sp. The latter 

 when collected had been captut-ed by an ant, Formica fusca L. (No. 

 102). A dead beetle, Dipolataxis liberta (102), was collected under aflat 

 rock. 



Spiders are abundant, especially Drassus neglectus Keys (No. 101), 

 Cicurina arcuata Keys (No. 102), and Lycosa pratensis Emer. (103). 

 The former builds a small pocket-like web 2 by 3cm. in cavities under 

 rocks, at a depth of about 1 dm. Spider egg cases were frequently found 

 under stones or in rotten wood (No. 102). 



Myriapods were rarely seen. They seem to have regular runaways 

 excavated thi*ough the wood or soil (No. 103). A dead caterpillar was 

 also <found under a rock (No. 102). 



Besides the numerous dead shells of Polygyra alholahris Say (Nos. 23, 

 27, 81, 187) which are common on the ground, especially near dead 

 logs, others were taken below ground. They occur at a depth of 1-2 dm. 

 under angular rocks, or at a less depth under larger flat rocks. In 

 either case their presence seems to be controlled by the moisture (Nos. 

 81, 102). Other shells were also rather common under rocks, especially 

 flat ones at a depth of 1 dm. or less (81). This single collection in- 

 cluded Pyramidula cronUicitei anthonyi Pils., Zon/itoides arborcus Say, 

 Yitrea Mnnojana (Nise), Sfrohilops virgo (Pils.). Under angular rocks 

 down to a depth of 1.5 dm. Pyramidula cronkheitei anfhontyi (Pils.) and 

 Zonitoides arhoreus (Say) were found. There are vei"y rarely more 

 than one under each stone. Most of them were dead, and the shells 

 were frequently broken, but a few were alive. At but one place were 

 they associated with a Polygyra, and in this case the Polygyra was 

 sealed with a membrane across the orifice and was probably still alive. 

 No shells were ever found under rocks with ant's nests. 



One jumping spider, Lycosa pratensis Enaer. (103), was caught on a 

 dead jack pine tree, 6 dm. from the ground. 



The fly {Hydrophorus. philonibrius Wheeler) already observed on 

 beaches and clearings was again common. Ordinarily they fly about 

 near the surface in the sunniest places, alighting on the ground or on 

 low plants. As soon as any moist soil is exposed they congregate on 

 it in numbers, crawling over the surface, into ant burrows, and even 

 apparently attempting to eat the ant pupae. One species of ant was 

 seen catching them. 



Among other insects were bumblebees, Bomhus sp. (23), visiting the 

 flowers of Diervilla dicrvilla; grasshoppers Vircotcttix verruculatus Kby. 

 (27); cicadas, Tihiccii rimosa Say, var. (28, 84), frequent in the pine 

 trees. 



VIII. The Balsam-Spruce Forest. 



The ultimate tendency of all plant associations on Isle Royale is 

 toward the balsam-spruce forest. The succession is sometimies direct, 

 sometimes indirect; sometimes rapid, as upon the smaller Cladonia 



