48 



Seasonal Succession of the Species 



That the different species of May-beetles do not make their first 

 appearance on the wing in spring at the same time is a fact familiar 

 to all collectors, but the actual order of their succession is not easy 

 of determination. Species rare in any locality are much less likely 

 than abundant ones to be taken at the very beginning of their period 

 of activity ; even the same species may seem, consequently, to differ 

 in position in the seasonal list in different years according as it is 

 relatively abundant or relatively scarce; the position of a species in 

 the seasonal list may differ in different parts of the state, since the 

 assemblage of species themselves will be different ; a species sensitive 

 to cold may be relatively early in the south and yet relatively late in 

 the north, where its activities are restrained by too low a temperature ; 

 an apparent difference of date between two species may be due to the 

 fact that collections were not made from their respective food-plants 

 at the same times ; if collections from lights are depended on, it may 

 easily happen that the distances from these lights to the places where 

 the different May-beetles breed and emerge most abundantly or to the 

 food-plants on which the different species assemble, are widely differ- 

 ent ; or the abundance of these food-plants in the neighborhood of the 

 lights may differ so widely that, of equally common species, some may 

 appear in collections abundantly and early and others sparingly and 

 late; the various weather of different seasons and of different parts 

 of the same season may have its disturbing influence ; and finally, in 

 our case, these differences of successive years in respect to the distri- 

 bution of our collections in time, space, and food-plants must have 

 introduced differences in succession which are artificial and apparent 

 only. The subject is, nevertheless, sufficiently important to those who 

 would understand the economy of our May-beetle population to make 

 it worthy of careful inquiry. 



For this purpose I have prepared tables showing the precise dates 

 on which all our dated collections of each species were made, in each 

 part of the state and in each of the four years from 1907 to 1910 

 inclusive, the species of each table being arranged substantially in the 

 order of their first appearances in spring. In a few cases this order 

 has been slightly changed where the mass of one species appeared 

 earlier than that of another, even tho the first collections of the latter 

 might have antedated a little those of the former. By a comparative 

 study of these seasonal tables, all necessary allowances being made for 

 differences in abundance of the various species in the collections of 

 each year, it seems possible to arrive at a fairly correct idea of the 

 normal order of succession of the more important kinds of May-beetles 

 for northern, central, and southern Illinois respectively — the succes- 

 sion which would be exhibited if collections were sufficiently numerous 

 and so distributed in space and time as to draw at each collection in 



