June, 1902] 



PSYCHE. 



357 



in the early morning liours and often not 

 even tlien. Spring is also the only sea- 

 son in which we can count with certainty 

 on securing guests of ants without extra 

 trouble. Later in the year success is 

 very doubtful, unless one happens, for 

 instance, to strike the e.xact time when 

 some of them, as Xcnodusa cava Lee, 

 eiTect a change of hosts. 



Formica exsectoides For., easily recog- 

 nizable by its shining abdomen and 

 slightly concave occiput, is the second 

 species which builds its formicary in the 

 shape of a hill. But these hills are 

 usually much lower and flatter. In any 

 case they never approach in shape the 

 truncated cones of F. obsciiripes. Nor is 

 there to be noticed so great a regularity 

 in their structure. They sometimes 

 resemble heaps of dirt dumped out at 

 random. Besides, they consist for the 

 most part of earth, although the latter 

 is often mixed with vegetable remains. 

 A favorite location of their nests seems 

 to be some clearing in the brushwood. 

 At least I found several nests on such 

 spots and when, owing to frequent dis- 

 turbances on my part, the ants preferred 

 to change their domicile, they established 

 their new dwelling in a precisely similar 

 situation. The nest entrances are dis- 

 tributed without any apparent order. 

 At any rate, they are not located merely 

 "at the base and about the periphery." 

 Formica exsectoides is one of the ants 

 most frequently met with in this region, 

 and often tiieir colonies consist also here 

 of ten and more nests.* 



*iBy the way, Forel maintains to have ascertained that 

 "unlike the exsecta of Europe these ants have not the in- 



Whereas the two preceding species 

 habitually build hills, they are to be 

 found rarely or not at all with the follow- 

 ing species. Thus they are rather rare 

 with Formica riil>icunda Em. and Formica 

 dakoteiisis Em. The cause of this may 

 be partly ascribed to their slaves, which 

 generally do not construct real mounds. 

 Of the two species just mentioned F. 

 riibiciinda., which may be easily recog- 

 nized by its subsericea-abdomen, with 

 almost unvarying constancy builds within 

 and around the stumps of trees, which 

 then present the following appearance. 

 The remains of some sturdy oak are still 

 standing firmly in the ground and are 

 surrounded by leaves, twigs, etc. Merely 

 a few entrances, which happen to exist 

 in the trunk itself or have been con- 

 structed through the sod near the roots, 

 establish communication with the inte- 

 rior. In such cases the use of explosives 

 is almost unavoidable in order to lay 

 bare the inner sanctum. Now and then 

 the nests built by rubicunda are exceed- 

 ingly similar to those of F. subsericea. 

 This happens whenever the superior 

 number of slaves exerts a greater influ- 

 ence on the structure of the nest. For- 

 viica dakfltensis, on the contrary, finds 

 its home usually under some flat stones 

 and mostly so, as far as I could observe, 

 when they have slaves. In the latter 

 circumstances the nest presents the ap- 

 pearance as if two different "architects " 

 had "evolved the plan." It is half 



stinct to seize their enemies by the neck in order to saw it 

 apart." .According to my observation the analogy with 

 their European congeners is complete also in this partic- 

 ular, so far as southwestern Wisconsin is concerned. 



