Explanatlon ol the Female Dimorphism of 

 Paltostoma torrentium^). 



In his paper on ''Paltostoma toro'entinm, eine Mücke mit zweigestaltigen Weib- 

 chen" (Kosmos, vol. VIII. pp. 37 — 42), my brother Fritz Müller siipposes that this 

 species of Blepharoceridae originall}^ was blood-sucking, but in later times changed 

 its habits and became fond of flower-nectar. In the males, who need only little food, 

 this change of habits and the corresponding change of the mouth-parts was accom- 

 plished, my brother supposes, more rapidly and perfectly than in the females, who, 

 maturing eggs and passing the winter, stand in need of more albuminous food 

 than the males do. Whilst therefore in some females of Paltostoma torrentiitm 

 the same change of habits and mouth-parts has taken place as in the males, other 

 females have still more or less continued their orig'inal blood-sucking habits and 

 preserved their original blood-sucking instruments. 



This explanation given by my brother is not yet proved by any direct 

 Observation of Paltostoma' s habits. He mentions, as an indirect argument for 

 his opinion, that in several Diptera the females have been stated to be blood- 

 sucking, whilst the males take nectar of flowers. It may therefore be worth 

 Publishing, that in Empis pimctata really just the same takes place as m}'- brother's 

 explanation of the female dimorphism in Paltostoma torrentiiim requires to be 

 supposed : males who exclusively feed on flower-nectar, besides females, both 

 enjoying flower-honey and attacking living animals and sucking their blood. 

 Several weeks ago (May 26) a great many males as well as females of Empis 

 punctata roved on the flowers of hawthorn {Crata'gtis oxyacantha). The males 

 were exclusively occupied with sucking nectar. Of the females some did the same, 

 whilst others attacked, murdcred, and consvmied the most clever visitor of flowers 

 among all our Syrphidas, Rhingia rostrata. 



Hermann Müller 



I) Nature 1881. Vol. XVIV. p. 214. 



Fritz M ü 1 1 e r s gesammelte Schriften. 95 



