THE POLLINATION OF THE PRIMROSE 341 



as pollinating agents, though the mites (Trombidium) which infested 

 several flowers at Erbistock on one occasion would be as effective as 

 Thrips in aiding self-pollination. Spiders have been seen on several 

 occasions in different localities waiting on the flowers for victims. 

 Burkill (I. c.) has recorded the similar habit of an Araneid (Xysticus 

 pini), which he observed lurking on the capitula of Coltsfoot and 

 Daisy, where pollination could certainly be brought about by such an 

 agent. In the case of the Primrose, old spiders may now and again 

 aid as pollen-distributors to a limited extent, and may occasionally 

 assist in autogamy of the short-styled flowers. Coleoptera are regular 

 visitors, feeding upon the pollen and petals. Some eighteen species 

 have been observed, most of which were previously unrecorded. This 

 is doubtless due to the fact that the observations of previous writers 

 were confined to the daytime, while many beetles are characterised by 

 nocturnal activities. From what I have seen of their habits and 

 structure I have no doubt that such Coleoptera are often of value in 

 bringing about pollination. 



There can be no doubt that the handsome bee-like Bombylii are 

 of considerable importance in pollinating the Primrose : the observa- 

 tions in North Wales and Sussex fully confirm those of Briggs and 

 Weiss in South Devon and Shropshire as to the frecpiency of such 

 visitors. These flies are entirely anthophilous and suctorial, with 

 long, projecting, conspicuous probosces, which are excellently adapted 

 for'probing such a tubular flower as the Primrose. Bombylius major 

 has a proboscis of 10 mm. in length ; in the case of the other Primrose- 

 haunting species (£. discolor) it is rather longer (11-12 mm.) : B. 

 major appears to be the more common. On visiting a Primrose, the 

 fly pushes its hairy head into the aperture as far as possible, so that 

 it is able to secure nectar at a depth which may be more than the 

 length of its proboscis would suggest. It is quite probable that in 

 some of the larger flowers the nectar may be out of reach, though it 

 does not follow that Bombylii would avoid them on this account, as 

 H. Muller (Fertilisation of Flowers, p. 43) has shown that the 

 proboscis is provided with effective piercing structures which can 

 easily penetrate soft tissues. He has often seen them insert their 

 proboscides into various nectarless flowers ; in such cases he supposes 

 that the boring apparatus was being employed. Whether Bombylius 

 evinces any discrimination or not as regards Primroses with longer 

 corolla-tubes than usual I cannot say ; but it has a characteristic 

 habit of hovering while apparently selecting particular blossoms 

 before alighting. It seems strange that Darwin and other observers 

 should have failed to detect these important pollinating agents 

 at work. On the other hand, Bombylii are essentially sun-lovers 

 and comparatively inactive in the absence of sunshine or in cold 

 exposed situations. Although our knowledge as to the distribution 

 of Diptera in Britain is very scanty, it would appear ( Verrall, British 

 Flies, v. 496-9 ; 1909) that B. major and B. discolor are not un- 

 common in the southern half of England, the latter being specially 

 noted for Sussex where it occurs in "all large woods and even open 

 roadsides." B. major would seem to have a wider range, as it has 

 been seen in the south of Scotland. 



