190 Annals Entomological Society of America [Vol. XIII, 



8. HYMENOPTERA.* 



By T. D. A. CocKERELL, University of Colorado. 



In discussing the life history of the Hymenoptera, we 

 naturally turn more especially to those problems which center 

 about metamorphosis on the one hand, and parasitism on the 

 other. My work on fossil insects has caused me to speculate 

 on the origin of these habits and characteristics, without 

 enabling me to reach any definite conclusion. To many, 

 these speculations will doubtless seem rather futile, yet no 

 intelligent person travels a road without some thoughts about 

 his journey's end. Hypotheses not only quicken the imagina- 

 tion, but at once increase the significance of every scrap of 

 information which tells for or against the opinions one has 

 formed. Thus the discovery of a fragment in some ancient 

 rock becomes a dramatic event. 



Overlooking the town of Boulder is a hill from which one 

 can look north across the flank of the front range. A series 

 of red rocks, now standing on edge, once formed the shore of 

 the Upper Carboniferous sea. A narrow valley separates these 

 from another sharp ridge, belonging to the lower part of the 

 Upper Cretaceous. It is interesting to look at these strata and 

 realize that in the interval between the first and the second, 

 the typical flowering plants, the birds, the mammals and the 

 insects with complete metamorphosis all came into existence. 

 Were these striking events accidentally coincident, or was 

 there some causal connection between them? The sea was the 

 mother of life and the land was discovered, so to speak, by 

 successive types of organisms. During the Carboniferous, 

 the terrestrial arthropods, especially the insects, were abundant 

 and often of immense size. The Amphibians represented an 

 invasion of the vertebrates, doubtless preying upon the rich 

 insect fauna. Reptiles, with hard-shelled eggs, finally solved 

 for the vertebrates the problem of completely terrestrial exist- 

 ance. Birds and mammals must have owed the possibility 



*I took part in the symposium as a substitute for another, to whom the topic 

 had first been assigned. I prepared no manuscript, and indeed have no special 

 knowledge of the matters which I should have discussed. It has not seemed 

 worth while to compile a summary from the literature, in order to secure approxi- 

 mate uniformity of treatment. 



