4IO Btdletm American Museum of Natural History. [Vol. XXII, 



even 1.5 m. The cone of the exsecta nest is, speaking more precisely 

 a crater, consisting of soil and felted plant growth, filled in at the top 

 with dry vegetable detritus. The nests therefore belong to Forel's 

 'combination nests,' in which an earthen substructure is combined 

 with a superstructure of plant detritus. The exsecta nest is peculiar 

 in having the earthen portion much more extensive than the top and 

 enclosing it like a crater. " 



The development and decay of the nests of this ant have been 

 studied near Aborrtrask in Gellivare, Lapland, with results that show 

 a remarkable similarity to the conditions above recorded for the 

 American exsectoides , if we make due allowance for the fact thai* the 

 European ant nests in damp meadows or bogs whereas our American 

 species prefers dryer soil or even hill-slopes covered with open woods. ^ 



I here reproduce the summary of Holmgren's observations: 



" I. The ant-hills in the willow zone are larger, but less numerous 

 than those in the Sphagnum zone of the bogs. The greater size 

 depends on the accessibility to more abundant building materials. Their 

 smaller number is likewise attributable to the same conditions, since 

 a greater number of ants are constrained to secure their food and 

 building materials in a relatively small area. Migration for the 

 purpose of founding new nesting sites is unnecessary on a large scale 

 where food and especially building materials are abundant. Access 

 to an abundance of the latter also explains the fact that in the willow 

 zone the nests are not overgrown by Polytrichum strictum, for here the 

 ants can inhibit the invasion of the moss by uninterrupted building. 



"In the Sphagnum zone, however, building materials are scarce 

 and on this account the ant colonies must be smaller and migration 

 occurs on a larger scale. This accounts for the smaller size and greater 

 number of ant-hills in this zone. 



"In the damp bog, building materials are relatively very scarce. 

 Here the hills are very much reduced in size and number. Owing to 

 the moisture in this zone there are few spots that will permit the ants 

 to build hills, for these insects require rather dry soil in which to 

 establish themselves. 



"2. The position of the hills in damp places prevents the ants 



'There are in America two other forms closely related to F. exsectoides, namely F. exsectoides var. 

 opacive^t'-is Emery and F. tdkei Emery. The former is known only from Colorado, where it nests 

 in dry, open situations at an altitude of 6000-8000 ft. Its nest-cones resemble those of the typical 

 exsectoides in shape but are covered with pebbles instead of vegetable detritus. F. rdkei which is 

 unquestionably a boreal species, was originally described from South Dakota, but I have recently 

 received worker and female specimens from Nova Scotia. Its nesting habits are unknown but 

 probably resemble those of exsecta or exsectoides. 



