DIPTERA— HOVER-FLIES 179 



to pollen-transference. Perhaps, too (according to Loew), the extremely well-developed 

 hairy covering of the eyes of numerous flower-visiting flies is a similar adaptation, 

 although this character is also possessed by many species that do not visit 

 flowers. 



In observing hover-flies at vcork among flowers, the impression is forced on 

 us that they delight in gaudy colours that are disagreeable to us. I observed that 

 even artificial flowers fastened to a lady's hat exercised a powerful attraction on 

 a medium-sized species of Syrphus, so that it persistently hovered in the air in front 

 of the flower, now and then darting to the side, but soon again to return to its former 

 position. Hermann Muller (' Befruchtung,' p. 278, note) describes the conduct of 

 Syrphus balteatus Deg. when visiting the flowers of Verbascum nigrum as follows : — 

 ' The behaviour of this beautifully coloured hover-fly clearly proved to me its well- 

 developed colour-sense. I watched it for over a quarter of an hour from a very 

 small distance, without disturbing it by my presence. It hovered for a considerable 

 time (ten seconds or more) at the same spot in front of the beautiful flowers 

 6-10 cm. away, to all appearance absorbed in gazing at them; it then rapidly 

 darted forwards, touched one of them for a moment, and immediately retreated. 

 After these manoeuvres had been repeated a number of times, until the insect 

 had gloated over the sight of the flower to satiety, it alighted upon a petal, seized 

 the middle of a filament with the fore-legs, and its lower part with the hind-legs, 

 and began to loosen and grind the pollen for itself by actively moving the flaps of the 

 proboscis to and fro. After carrying on this operation for five to ten seconds or more, 

 it worked for some seconds with its flaps among the club-shaped violet hairs of the 

 filament, and then went to another stamen of the same flower, treating this similarly. 

 It also licked and pollinated the stigma. After having fed sufliciently from a flower, 

 it renewed the hovering and gazing already described.' 



Miiller also observed (' Fertilisation,' pp. 440 and 80) the similar visits of Syritta 

 pipiens L. to Veronica Beccabunga L. and of Eristalis intricarius L. to Caltha 

 palustris L. The delicate little Syritta, enjoying the sunshine, hovers in one place 

 before the beautiful blue flowers of Veronica Beccabunga, approaches it backwards, 

 and then hovers again, till suddenly with a fresh dart it settles on a blossom. The 

 beautifully tinted hover-fly Eristalis intricarius when visiting the flowers of Caltha 

 also shows very clearly the pleasure it takes in bright colours. Just as the male 

 Eristalis is wont to hover in its love-sport above the female, so does this insect often 

 poise itself for a considerable time over one of the golden-yellow flowers, suddenly 

 darts down upon it to suck nectar or eat pollen, and then flies abruptly above 

 another blossom, there to repeat the same conduct. 



This noteworthy proclivity of hover-flies, which can be observed on all occa- 

 sions, indicates that they possess marked preferences with regard to choice of flowers, 

 and it is therefore intelligible that special 'hover-fly flowers' (see pp. 135-6) should 

 have been evolved. 



With regard to the visits of Syrphidae to flowers, I have shown ('Bliitenbesucher,' 

 II, p. 11) that though they are specially attracted by social flowers, they neverthe- 

 less seek with almost equal zest flowers with half-concealed or exposed nectar, and 

 more rarely those with entirely concealed nectar, provided this is hidden at a level 

 corresponding to their proboscis, which is usually of medium length. The}' also 



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