February, '10] piske : superparasitism 91 



eral experiments which have been planned and executed for the ex- 

 press purpose of determining this point have indicated in each instance 

 that the reproductive capacity of two parasites which developed on a 

 host just large enough for one, was very much less, combined, than 

 that of one developing under otherwise identical conditions. In one 

 instance in particular, although several times as many individuals 

 were secured as the result of superparasitism, they were unable to 

 reproduce at all. It is, therefore, evident that the indirect results of 

 superparasitism may be greatly to the disadvantage of the parasite, as 

 weU as the direct results following the premature death of the host. 



Classified somewhat more formally, the manifestations of super- 

 parasitism are as follows : 



(I) One parasite lives ; the other dies. 



(a) The survivor preys upon the other as an accidental sec- 



ondary parasite. Of common occurrence. 



(b) The survivor destroys the other by bringing about prema- 



ture death of the host, and may or may not devour it 

 incidentally. Of common occurrence. 



(II) Both parasites live. 



(c) Neither are the worse for the circumstances. Very rare. 



(d) One or both are so seriously weakened and stunted as to 



bring about a material reduction in their capacity for 

 reproduction. Common. 



(III) Neither parasite survives. 



(e) This may be brought about through premature death of 



the host through excessive parasitism (commonly) ; or, 



(f ) Through inability of either parasite to complete its trans- 



formations on the limited supply of food. Common. 



Instances illustrative of several of the above conditions were men- 

 tioned in the paper upon the parasites of the Saturniidae, to which 

 reference has already been made. 



It is interesting and important, in this connection, to note that in 

 those instances which fall in di\asion I, the surviving parasite is not 

 infrequently seriously dwarfed and proportionately weakened. The 

 results, therefore, are equivalent to those obtaining in section III. 



Prevalence. The prevalence of superparasitism depends entirely 

 upon whether or not the female parasite is gifted with a prescience 

 which will enable her to select healthy hosts for her offspring. Pre- 

 supposition that she possesses this instinct is equivalent to a denial of 

 the existence of superparasitism. This is indubitably not in accord- 

 ance with conditions as they exist in the field and laboratory. 



