1986] Herbers & Tucker — Leptothorax longispinosus 227 
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Figure 4. Schema of changes on floor 1 A in late July. 
separate experiments where 2 nests of L. longispinosus were posi- 
tioned naturally on floors. They also examined the closely related L. 
ambiguus, for which fusions occurred in 16 of 21 replicates. Their 
experiments were apparently conducted on nests collected from 
spring through mid-summer, which probably included parts of 
polydomous colonies. That we observed only 2 fusions in a com- 
parable study may reflect the fact that we placed functional colonies 
on our floors; a lower fusion rate would be expected for entire 
colonies than for subunits of polydomous colonies. 
In contrast to fusion events, reports of spontaneous polydomy 
show rough similarity between species. Stuart (1985) found that 12 
of 57 nests of L. curvispinosus underwent fission in the laboratory, 
events that were dispersed throughout the season. Our fission rate (4 
events for 17 nests) is quite comparable, although we observed spon- 
taneous polydomy primarily in spring. Thus fission events may not 
be as strongly seasonal as our results imply. 
The above data are entirely consistent with the cyclic polydomy 
hypothesis, since activities associated with colony fractionation 
(brood transport, tandem running, fissions, worker exchange) 
occurred mainly in early spring. The fluid nature of this L. longispi- 
nosus population is quite evident, and can help to explain summer- 
winter differences in queen and worker distribution (Herbers 
1986a). The causes of cyclic polydomy are obscure at present. Col- 
ony fission during spring and summer may serve to alleviate compe- 
tition for food (Herbers 1985), but nest coalition in fall is more 
