November, 1923. The Irish Naturalist. 109 



THE LARVA OF A HYDROPHILID BEETLE, 

 MEGASTERNUM BOLETOPHAGUM. 



BY K. C. JOYCE PHILLIPS. 



The larva described in this paper was found by Mr. James 

 L. McWhinney, A.R.C.Sc.L, in the course of the investiga- 

 tion on the fauna of a pasture soil, in which he is engaged 

 at the Albert Agricultural College, Glasnevin. For the 

 purpose of this research, samples of soil are taken from a 

 field in permanent pasture at intervals of a week or ten days, 

 each sample being a nine-inch cube, which is divided into 

 five horizontal layers, the topmost an inch, and the other 

 four two inches in depth. The live animals found in each 

 layer are counted and identified as far as possible, larval 

 insects being kept for rearing ; this is specially desirable 

 in the case of larvae of which no description appears to be 

 available. 



In the topmost layer of a sample taken on 6th February, 

 1922, two small unknown beetle-grubs were found. They 

 were of a dirty pale brown colour, difficult to see in the 

 soil when at rest, with large head and conspicuous asym- 

 metrical mandibles, the remarkable appearance of which 

 at once aroused curiosity. The larvse moved forward at 

 a steady rate, the mode of progression being quite distinct 

 from that of a maggot. Similar larvae were seen in most 

 of the samples taken until May 22nd, and they were always 

 found in the topmost layer, that is within an inch of the 

 surface. Most of them, unfortunately, died, but two 

 specimens pupated in I\Iay, and the adult beetles emerged 

 on i8th June. Mr. J. X. Halbert, M.R.LA., of the National 

 Museum, kindly identified these as Megasternum holeto- 

 phagum Marsh, one of the smaller Hydrophilidse common 

 in most parts of Ireland. Reference to Schiodte's great 

 work on beetle-larvae showed that a similar asymmetrical 

 condition in the mandibles is characteristic of the allied 

 Cercyon analis Payk.^ As no larva belonging to the 



ij. C. Schiodte : De Metamorphosi Eleutheratorum Observationeti. 

 Natiirh. Tidsskr. (3) i., (1861), pp. 219-20, pi. vi., figs. 16-25. 



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