SCIENCE-GOSSIP. 



345 



Large Swan Mussels. — Some children friends 

 found last autumn shells of the Swan-Mussel 

 (Anodonta cygnea) in the lake at Englefield, in 

 Berkshire, which was almost dry at the time. 

 These shells have been sent to me, and prove to 

 be exceptionally large. The greater of them is 

 nearly nine inches long, and more than ten and a 

 haK inches at the extreme girth of the shell. Can 

 any reader tell us anything about the approxi- 

 mate age of the animals bearing these shells ? 

 — Mrs. Emilt J. Climenson, Henley-on-Thames. 



The Sinqing-Flt. — Some months since there 

 appeared in a local journal a notice respecting 

 certain insects presented to the Natural History 

 Museum, South Kensington, by our townsman, 

 Mr. C. J. Watkins. In this notice special mention 

 was made of the dipterous fly Stncomyia borealis, 

 popularly known as the singing-fly, which, it 

 is said, has the ability to emit a peculiar sing- 

 ing sound without any vibration of its wings. 

 It may here be pointed out that this power of 

 emitting sound is not by any means confined to 

 one member of this family of flies, since it is 

 shared, in a greater or less degree, as far as my 

 observations have gone, by nearly every species 

 when resting on leaves in the sunshine. Some few 

 years ago I was much engaged in the preparation 

 and mounting of the diptera for microscopical 

 purposes, collecting my Syrphidae after sun-down 

 from the vmder side of leaves. When walking on 

 a pathway skirting a flower border, I have 

 frequently been attracted by the musical sound 

 emitted when the creatures were resting on a 

 leaf in the bright simshine, and could never detect 

 the slightest vibration in their wings. Mr. C. J. 

 Watkins, who spends no little time in one of the 

 richly-wooded coombes greatly affected by these 

 flies, tells me that they frequently settle upon his 

 coat-sleeves and entertain him with their pipings. 

 He states that he has distinctly observed a very 

 slight but rapid vibration of their wings. I 

 cannot, however, help thinking that he is mis- 

 taken. One thing seems tolerably certain : if the 

 Sericomyia borealis has power to emit the sound 

 when apparently perfectly quiescent, then it may 

 safely be assumed that other species of the family 

 have power to do likewise. If, however the 

 Syrphidae, more frequently observed, emit their 

 music by the rapid, though unseen, vibration of 

 their wings, then it may as safely be assuxned 

 that the so-called singing-fly produces its music 

 in a precisely similai; manner. There is a Syrphus 

 which almost invariably produces the sounds when 

 at rest in the sunshine, and suiEciently loud to 

 attract attention when one is passing the plant 

 on which it is resting. This insect is about half 

 an inch in length, with very large red eyes and a 

 dark thorax, beautifully shot with iridescent 

 colours. I have always attributed this sound to 

 one of distress, as on one occasion, when the 

 creatiure was making an unusually loud noise, it 

 was with its two fore-feet endeavouring to divest 

 itself of a red parasite firmly attached to its 



proboscis. I have, too, often observed, when 

 captiu'ed and lightly held between the two first 

 fingers and thumb, so as to imprison but not hurt 

 the fly, that it has emitted a particularly loud 

 and plaintive sovmd. In this sitviation it is 

 evidently impossible that any vibration of the 

 wings could take place. Whilst on the subject of 

 Syrphidae, another fact may be noted concerning 

 these dipterous flies. They are not, as so fre- 

 quently asserted in books, honey-loving flies. In 

 some works on natural history it is stated that, 

 after hovering over a flower, they will, with 

 astonishing velocity, dart into the cup to sip the 

 nectar therefrom. Although it cannot be sup- 

 posed that the whole statement is a pure 

 fabrication, it is, nevertheless, full of error. It 

 would indicate that the honey was spread upon 

 the petals of the flower, and that all the Syrphus 

 had to do was to dart at it and take its fill; 

 whereas every botanist knows that the honey is 

 secreted in the nectary of a flowex*, almost 

 invariably difficult of access, and requiring 

 special organs for its extraction — such as the 

 tongues of the honey- and humble-bees, or the 

 astonishingly-long proboscis of some butterflies 

 and certain moths. Nor, as may be at once seen, 

 does the proboscis of the Surphus in any wise 

 resemble those of the bees. The fact is that the 

 Syrphidae are pollen- and not honey-feeders, as 

 any entomologist may readily prove. Let the 

 student do as I have so frequently done for 

 microscopic preparations, pkmge the insect into 

 liquor potassae. When the contents of the body 

 have been partially dissolved by this powerfvil 

 solvent, gently press the insect in the usual 

 manner between two pieces of plate glass, so as 

 to express the contents through the posterior 

 part of the abdomen ; where this is not trans- 

 parent and empty, or nearly so, as very frequently 

 happens, a quantity of greenish or yellowish 

 substance is squeezed out. This will be found to 

 consist of pollen grains, usually from three or 

 four different species of flowers. Even after thus 

 squeezing out seemingly the whole contents of 

 the abdomen, upon examination, when fully 

 prepared for the microscope, it will be seen that 

 it still contains hundreds of grains, the majority 

 of them consisting of pollen from the Umbelli- 

 ferae, which are mostly affected by these flies, 

 notably by Bhingia rost7'ata. In two mounted 

 specimens lying before me, each contains a vast 

 number of grains from three species of flowers. 

 Some of them are of enormous size relatively to 

 that of the insects, others of medium size, and 

 some small. It is a subject of continual wonder- 

 ment to me how these flies contrive to get these 

 pollen balls into their stomachs, so large are they. 

 It is as though a man swallowed whole platefuls 

 of large oranges, sundry apricots, and hundreds 

 of greengages. I am not by any means prepared 

 to deny that any species of the Syrphidae have a 

 taste for or can collect honey, but, so far as my 

 observations are concerned, the species are few. 

 I have, during the autumn months on warm 

 sunny days, when the ivy blossom is literally 

 alive with both dipterous and hymenopterous 

 flies, noticed that Eristalis tenax will be found 

 amongst them, claiming his share of the sweets. 

 These, however, as every botanist knows, can 

 be licked up without difficulty. — Edward H. 

 EoBERTSON, Woodville, Greenhouse Lane, Pains- 

 wick, Gloucestershire. 



