1926] Sequential Distribution of Formica exsectoides Foret 137 
the above process of substitution of younger for older did not 
succeed in any one mound. Of external inimical factors there 
are many, such as man’s culture of the field, his domesticated 
animals tramping on ants and the mounds, his direct hostile 
acts and the attacks from animals that feed on ants, as the skunk 
and the woodpecker, also adverse influences of mosses and other 
vegetation. In this Timonium region, the direct causes of the 
extinction of life in moulds are not at all known. 
On the other hand the differential dying off of many mounds 
in one part of the area and the coincident appearance of new 
mounds in another section of the area is a phenomenon that may 
be correlated with environmental factors. As far as known 
important enemies of the ants are largely absent from the whole 
area and as impotent in one as in another section of the region 
and the success or the failure of groups of mounds would seem 
more likely due to some factors that have changed slowly through 
the many years. 
As in general Formica exsectoides is found where there are 
trees but not dense old forests, it may be regarded as a dependent 
upon certain stages of forestation. 
In the north region of the diagram during the slow dis- 
appearance of so many mounds there was greater growth of the 
trees and increase in their age. In the middle region the inrush 
of new mounds in fifteen years has been accompanied by the up- 
springing of a new growth of young trees. 
This correlation of many new mounds with new trees and 
many empty mounds with old trees may well be significant. It 
is supported by such facts as: the vestiges of old mounds in the 
region between the ant “town and village” where the woods are 
dense and old; the failure of a mound transplanted to the large 
woods of “Homewood” and its better success when the ants 
migrated spontaneously to the open edge of the wood in Wyman 
Park; the great success of colonies in the Holidaysburg region 
where mining operations kept the forest cut down in part; the 
present flourishing of a large colony in the cut-over forests of 
the neighboring Warriors Mark. (Andrews, Ent. News, 1925), 
and the observation that this ant in early spring is more active in 
regions of sunny exposure than in older woods. 
