REPORT OF THE STATE ENTOMOLOGIST I9O9 95 



land where hordes of the pest appeared, though none were ob- 

 served on either side. The only difference that was known 'to 

 exist between infested and uninfested territory was that the 

 infested territory had a little earlier in the season suffered 

 rather severely from a hailstorm. It is probable that the hail 

 destroyed enough of the grass so that the caterpillars were 

 compelled to seek food elsewhere, though under normal con- 

 ditions they would not have attracted notice. 



An army worm outbreak requires prompt treatment. Grass 

 or grain in badly infested fields, if of any value, should be cut 

 and removed at once and the migration or marching of the 

 hungry caterpillars prevented by digging slight ditches or. turn- 

 ing furrows toward the advancing horde. The ditches and fur- 

 rov/s can be made more effective by digg'ing small holes at 

 intervals of 15 or 20 feet in which the caterpillars turning to 

 either side, fall. They can then be readily destroyed by bury- 

 ing. Bands of tar are serviceable in checking the advance of 

 the pests and may be made more effective by putting the tar 

 upon boards and setting the latter on edge. Conditions occa- 

 sionally w^arrant the poisoning of a strip in front of the march- 

 ing caterpillars, in order to destroy them and prevent further 

 injury. Paris green, london purple or even white arsenic is 

 preferable for this purpose to the slower acting arsenate of 

 lead. Masses of caterpillars can be killed by liberal spraying 

 with a kerosene emulsion or a strong soap solution. Not in- 

 frequently these outbreaks are accompanied by the presence of 

 numerous natural enemies such as Tachina flies which are 

 similar to and larger than the ordinary house fly. These bene- 

 ficial parasites deposit oval, rather conspicuous white eggs on 

 the caterpillars, usually just a little behind the head. An 

 abundance of these flies or other natural enemies such as the 

 ferocious ground beetles may render it unnecessary to take ac- 

 tive measures for the destruction of the caterpillars, because 

 under such conditions there is comparatively little dang'er of 

 any number attaining maturity. On the other hand, indis- 

 criminate destruction of the parasitized caterpillars may result 

 in the annihilation of numerous beneficial insects. 



Luminous larvae ( P h e n g o d e s p 1 u m o s a Oliv.) . The 

 common lightning bug or more properly lightning beetle, 

 Photuris pennsylvanica DeG. is well known, though 

 its luminous larvae, occasionally observed in decaying wood, 



