134 



[November, 



tennsB and the upper apical portion of the posterior femora pitchy-black, 

 and the suture very slightly rufescent ; whilst in the darkest, the an- 

 tennse, head, posterior femora almost entirely and anterior and middle 

 femora slightly, apex of all the tibije and tarsi, and the suture (especially 

 behind), are pitchy. This darkness, however, I suspect must principally 

 be attributed to a mere suffusion of fluids in drying after death. 

 7, Park Field, Putney, S.W. : Uth October, 1868. 



ON THE ABUNDANCE OF CERTAIN INSECTS IN CERTAIN YEARS. 

 BY E. C. E. JOEDAN, M.D, 



It was formerly a favourite hypothesis with me that either the eggs 

 or pupae of some insects lay dormant until a favourable season for their 

 development ; but I am growing more and more weaned from this idea 

 yearly. I do not wish to deny that the pupae of Eriogaster lanestris, 

 for example, may pass over a year when February and March are 

 unusually bleak, but this latent state is not the reason for the periodic 

 abundance of certain insects. Every moth lays a vast number of eggs, 

 and generally the greater number of these perish before arriving at 

 maturity, the usual time for such destruction is probably the very young 

 stage of larval life, and a heavy rain about that period may cause great 

 mortality ; in some years all circumstances prove favourable, and the 

 usually rare insect becomes abundant. Some lepidopterous insects are 

 peculiarly subject to this periodic plenty, such as Golias B.yale and 

 Edusa (both I believe always abundant on the continent). Sphinx convol- 

 vuli, Agroiis saucia, insects of the genus Heliothu, and many others. 

 These remarks have occurred to me " in populous city pent," and with 

 too much work to touch entomology for the season, from the unusual 

 abundance of two insects in the streets of this town. They have been 

 Chrysopa perJa and Goccinella septempunctata. Of the former I counted 

 more than twenty on each of two consecutive lamps one night, and 

 every other lamp seemed to have an equal number ; as for the latter, 

 they have been so plentiful that I have seen children of ten collecting 

 them from the walls in little baskets and paper bags. Now it is well 

 known that the larvae of these two insects are subject to very similar 

 conditions as far as regards the general " struggle for existence," widely 

 different as the perfect states may be. These few remarks are given in 

 the hope that some interesting observations may be drawn out from 

 entomologists as to their experiences during the very peculiar and 

 almost tropical summer through which we have just passed. &yrphus 

 pyrastri has been only a little more plentiful than usual. 

 35, Harborne Road, Birmingham : Sept. \2thy 1868. 



