REPORT OF THE ENTOMOLOGIST. 305 



IMPOETANCE OF THE NATURAL ENEMIES OP THE COTTON-WORM — 



SUMMARY. 



From a perusal of this section it is doubtful if the reader has obtained 

 a very detinite idea of the actual amouut of good performed by the nat- 

 ural enemies of the cotton-worin, except that it is by uo means insignifi- 

 cant. It would, indeed, be a difiicult task to estimate the number of 

 cotton -worms, in one stage or another, that are destroyed every year by 

 the different birds and insects; but we will bring together in this sum- 

 mary such points as relate to the amount of good performed, hoping to 

 set the importance of the subject forth in a more definite light. 



Among the vertebrate enemies, it will be of interest in this connection 

 to be able to form an idea of the actual numher of insects destroyed by 

 the average insectivorous bird. As concise a statement of facts upon 

 this point as we have met with is given in Professor Anghe;^'s report 

 to the United States Entomological Commission. Professor Aughey 

 says : * 



Few unobscrv;int people have any comprehensiou of tlie vast number of insects that 

 birds actually destroy. During tlio breeding-season this destruction of insects by birds 

 reached its culmination. The young of some species will cat about 50, others about 

 60, some about 75 insects each day. The average cannot be far from 60. At this rate 

 five young birds would eat about 300 insects each day, or about 9,000 a month for each 

 mouth, exclusive of the parents. There have been widely different estimates as to the 

 numberof insects that the old birds eat, but it ought not to be difficult to api)ro5imate 

 the quantity. Only a small part of a bird's stomach is entire enough to be distin- 

 guished a.nd counted. If the balance is composed as largely of insects, which is more 

 than probable, then the whole number eaten during a day by an insectivorous bird 

 must be near 200. I reached the s.ame conclusion by actual tests. In the fall of 1874 

 I bought two Bastrauiian jjlovers from some boys who had trapped them, and kept 

 them for a weelc in a cage before they were set free. I fed them om locusts and other 

 insects, which I counted for four days with the following result : 



First day 277 



Second day 452 



Third day 448 



Fourth day 4;^i9 



Total 1,016 



Average per day 4()4 



Average for each 'J02 



I was compelled to go away or else the experiment would have been continued 

 longer. 



About one-fourth of the insects were locusts, and the balance were flies, ants, beetles, 

 «fec. I gave them whatever insects the boys that I hired gathered for me. My im- 

 pression, however, is that they ate less than they would have done if they had"^been 

 at liberty. But, lest there might be some mistake, and to avoid all possibility of error 

 on the wrong side, we will base our calculations on an estimate of 150 insects each day 

 for a mature plover. At this rate 20 old plovers would eat 3,000 insects each day, or 

 93,000 a month. And suppose further that these 20 plovers had nests v.-hich averaged 

 four young ones each. At (K) insects a day (or each young [ilover the 40 would con- 

 sume 2,400 every twenty-four hours, or 72,000 a month. The 20 plovers and their 

 progeny together would consume 162,000 insects each mouth. At this same rate 1,000 

 plovers and their young would consume in one month 8,100,000 insects. That many 

 insects removed in one year from a farm of 160 acres would probably render it capable 

 of producing crops even when these insects were doing their worst. As there are 

 many birds that eat more insects than do the plovers, as well as many that eat less, 

 150 insects a day is probably a fair average for all insectivorous birds. 



This extract is eloquent as a defense of birds, and puts us on a sound 

 basis of a])parcntly unexaggerated facts. Too much, then, can hardly 

 be said in favor of insectivorous birds in cotton -fields. 



With the exception of the ants, predaceous insects are hardly to be 



'' First annual report of the United States Entomological Commission, 1877. Rocky 

 Mountain Locust, Department Interior, 1878. 



20 AG 



