136 - THE ENTOMOLOGIST. 



Diptera I have found at present almost confined to the 

 Syvphidae. In my own litlle garden, and in tlie gardens of 

 the Royal Botanic Society, in the Regent's Park, I have been 

 in the habit, during the last few summers, of capturing 

 specimens of the two most common species, Eristalis tenax 

 and Syrphus clypeata, eviscerating them, and examining the 

 contents of the abdomen under the microscope, which I 

 found to be coloured a bright orange, by the presence of 

 enormous quantities 'of the peculiar spined pollen-grains 

 characteristic of Composilae, and evidently obtained from the 

 various species of Aster, over which such numbers may be 

 seen hovering. That ihey are not accidentally taken up, but 

 form an actual article of food for the flies, is sufficiently 

 proved by finding them in every stage of digestion, the fluid 

 contents of the pollen-grains being apparently the nutritive 

 substance, and the skins being ultimately excreted. Speci- 

 mens of several species of Muscidae, captured on the flowers 

 of the Aster, when examined in the same manner furnished 

 only a very few grains of pollen, apparently sucked up acci- 

 dentally through the proboscis with the fluid food. During the 

 present spring I captured, on the flowers of the sloe, Eristalis 

 tenax and Andrena fulvicrus (male and female). The abdo- 

 men of the former was full of pollen-grains, belonging to at 

 least three kinds of plants, — the sloe, the dandelion, and 

 some large triangular pollen-grains, apparently those of 

 Fuchsia. The tubes of the latter species contained only a 

 very few grains, as was also the case with the honey-bee, the 

 pollen belonging in the latter case apparently to the dande- 

 lion. I was interested at the same time in watching the 

 constancy with which insects visit only the same species of 

 flowers on the same visit. In the case of a bank covered with 

 the white dead-nettle, red dead-nettle, and ground-ivy, the 

 white dead-nettle was visited only by one species of humble- 

 bee, Bombus Pratorum and Anthophora retusa; the ground- 

 ivy only by the hive-bee, except on two solitary occasions by 

 the Anthophora; while the red dead-nettle was entirely 

 neglected by both, the only insect observed to visit it being 

 a butterfly, Vanessa Urlica^. An examination of the pollen 

 carried away on the thighs of the hive- and humble-bees con- 

 firmed this observation, the pollen-grains of the three species 

 named being particularly easy to distinguish by their colour : 



