230 EXPERIMENT STATION. [Jan. 



shape on its very central portion sixty-eight days after the 

 removal of the flowage. The distance from the center of the 

 12-acre bog to the upland at the nearest point is about 250 feet, 

 as roughly measured by pacing. The IGO-acre bog, in the mate- 

 rial collected twenty-seven days after the flowage was taken off, 

 gave distinctly larger counts and showed a greater variety of 

 spiders near the upland than at the center. At the same time 

 some kinds of parasitic insects were collected near the upland 

 which seemed to be entirely absent at the middle of the bog. 

 The distance from the center of this bog to the upland at the 

 nearest point is about 750 feet, as measured by pacing. 



While it is evident, therefore, that winter flowage seriously 

 reduces the work of the natural enemies of the fireworm, espe- 

 cially on the large bogs, it must be remembered that in spite 

 of this handicap they succeed in doing a great deal toward con- 

 trolling this insect on all bogs and that, in the first beginnings 

 of the most damaging infestation, only a few stragglers here and 

 there succeed in escaping them. The escape of these stragglers 

 is, however, a serious matter, for they increase the amount of in- 

 festation which these natural enemies must take care of the fol- 

 lowing season (a slight infestation probably coming onto the bog 

 from the upland every year) if they succeed in keeping the pest 

 under control. As the winter flowage comes in and sweeps 

 away these natural enemies again, they cannot increase on the 

 bog to meet the increase in the number of fireworms. The fire- 

 worms, therefore, tend to increase in number, Avhile the number 

 of their enemies tends to remain constant from season to sea- 

 son on account of the flowage interference (the bog is here con- 

 sidered as being winter-flowed, but not reflow^ed at a time to 

 reduce the fireworms). When once the infestation has devel- 

 oped beyond the ability of the natural enemies of the insect to 

 control it, its increase is very rapid unless artificial aids to 

 these enemies are provided by man. Theoretically, the escape 

 of 2 straggler fireworms one jenr may mean the escape of per- 

 haps 50 the next year, and of perhaps 1,200 tlie third year, and 

 of 30,000 the fourth year, and so on. 



The point toward which we have been working in this discus- 

 sion is this: prohnhly tJie ideal time to spray for tins insect with 

 arsenical poisons, especially on the large compact bogs and on 



