THE STATE ENTOMOLOGIST. 129 



the present summer, it will suddenly be so subdued as not to be 

 noticed for some years to come. Its undue increase but combines the 

 assaults of its enemies, until they multiply so as to gain the ascend- 

 ency. Then, from insufficiency of food these enemies suddenly de- 

 crease in numbers, and their natural prey has a chance to increase 

 again. And so it goes on in the "Struggle for Life," and in the great 

 complicated net-work in which every animal organism is involved: 

 a check here and a check there, and no one of all the myriad 

 forms allowed to keep the ascendency beyond a limited time. The 

 most efficient cannibal insects in checking the increase of this Forest 

 Caterpillar, are the larger Ground-beetles belonging to the genus 

 [Fig. 54.] Colosoma. These beetles will pounce 



upon the worms with astonishing greed, 

 and are especially prone to attack them 

 when helplessly collected together during 

 the moulting periods. The Rummaging 

 Ground-beetle (Colosoma scrutator,. 

 Fabr.), which every one will recognize 

 from the figure (54), is especially fond of 

 them. The most common parasite which 

 occurs abundantly in the West, as well 

 as in the East, and which I have bred 

 from several other caterpillars, is a mag- 

 got producing a Tachina-fly, which differs 

 only from the Red-tailed Tachina-fly (Exovista leucanice, Kirk.), 

 which infests the Army-worm, in lacking the red tail.* The other 

 parasite which infests it in the East, but which I have not yet met 

 with, is a species of Pimpla very closely allied to P. melanocepJiala,. 

 Brulle, but differing from that species in the head being red and not 

 black.f 



SUMMARY. 



The Tent caterpillar of the Forest differs from the common Orchard 

 Tent-caterpillar principally in its egg-mass being docked off squarely 

 instead of being rounded at each end; in its larva having a row of 

 spots along the back instead of a continuous narrow line, and in its 

 moth having the color between the oblique lines on the front wings 

 as dark or else darker, instead of lighter than the rest of the wing. It 

 feeds on a variety of both forest and orchard trees; makes a web 

 which from its being usually fastened close to the tree is often over- 

 looked; is often very destructive, and is mosteasily fought in the egg 

 state. 



*Exorista Icucanim, Kirkpatrick = E. militaris, Walsh. I have bred the variety lacking the 

 red at tip of abdomen from larva; of Aitacus cecropia, Linn., Datana minis tra, Drury.. Agrotis , 

 inermis, Kilej', and of two undetermined Agrotidians. 



f Practical Entomologist, II, p. 114. 

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