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It has been ascertained that plants have a certain zone of temperature 

 outside of which it is impossible for plant-growth to take place ; and 

 also, that at a certain degree of temperature plant-growth proceeds 

 more rapidly than at any other degree. 



Now, from what we stated above, it is natural to suppose that 

 insects also have a zone of temperature, and also that at a certain 

 degree of temperature insect growth progresses more rapidly than 

 at any other degree. It is not to be supposed that the highest 

 degree which the air ever attains in our northern States exceeds the 

 zone of temperature in insects, as they appear to develop the most 

 rapidly during the hottest weather. In this latitude the tempera- 

 ture seldom exceeds 100'' Fahrenheit. Taking this for the degree at 

 which insects develop the most rapidly, it follows that as the tem- 

 perature sinks below this the development of insects is retarded in 

 proportion to the number of degrees which the temperature lowers. 

 During a wet season the temperature is much lower than during a 

 dry one. • This is easily explained by the simple fact that when the 

 rain falls upon the surrounding objects it withdraws from them a 

 sufficient amount of heat to evaporate it, and thus reduces their 

 temperature very materially. It follows that durmg such seasons 

 the life of the insects is greatly extended to what it would have 

 been in a dry season, and it is thus subjected to the attacks of its 

 enemies and diseases for a longer period ; and it is very probable 

 that when its temperature continues for some time above its natural 

 zone of temperature, that this alone would prove fatal to it, although 

 it is more likely that this would simply cause it to pass into a 

 lethargic or torpid state. 



The reason for this insect appearing in such great numbers dur- 

 ing wet seasons may be found in the following passages. 



A dry season nearly always precedes a wet one, and the inter- 

 vening winter is usually a steady cold one — just the sort best suited 

 to the successful hibernation of insects of all kinds. It follows that 

 during the dry season the Army Worms will become greatly multi- 

 plied, and the following winter being favorable to them, the major- 

 ity of them will hibernate in safety, and thus they will appear in 

 great numbers in the forepart of the following year. It is only the 

 midsummer brood of these worms that migrate ; and as the rain 

 seldom begins, in a wet season, earlier than the month of August, 

 this brood will have attained a sufficient size to travel from one 

 field to another, and commit their ravages, before the rainy season 

 fairly begins. In the months of June and July but little rain falls ; 

 and it is in this period that the Army Worms appear in the greatest 

 numbers. Later in the year, in wet seasons, the heavy rains occur, 

 and these very materially lessen the number of the worrns in the 

 succeeding broods, and thus prevent them from appearing in de- 

 structive numbers the following season, which is usually a dry one. 

 Moreover, the winter which follows a wet season is usually a mild, 

 open one, and this, contrary to the popular belief, is very unfavor- 

 able to the successful hibernation of all kinds of insects. 



We see, then, the reason why the Army Worms are so much more 

 abundant during a wet than during a dry season; and also that, 

 were two wet seasons to occur in succession, these insects would not 

 be so plentiful the second season as they were the first. 



