This section is from the book "On British Wild Flowers Considered In Relation To Insects", by John Lubbock. Also available from Amazon: Nature Series On British Wild Flowers Considered In Relation To Insects.
Fig. 27. - Right hind-leg of Bombus Scrimshiranus.
Fig. 28. - Right hind-leg of Hive-bee.
It is difficult to account for the relations which exist between flowers and insects, by the hypothesis of a mere blind instinct on the part of the latter.
Thus Sarcophaga carnaria visits Polygonum Bistorta in search of honey, although that flower does not contain any. Genista tinctoria again, though not melliferous, is visited by the males of several species of bees in search of honey. The same is the case with Ononis. H. Muller records a case in which he watched a female Humble-bee (B. terrestris) examining an Aquilegia; she made several vain attempts to suck the honey, but after awhile, having apparently satisfied herself that she was unable to do so, bit a hole through the corolla. Having thus secured the honey, she visited several other flowers, biting holes through them, without making any attempt to suck them first; conscious apparently that she was unable to do so He also observed a similar instance in relation to Primula elatior. In Vicia cracca and some other species, Bombus terrestris habitually obtains access to the honey by biting a hole at the base of the flower; and these holes are then subsequently used by other bees. Indeed anyone who has watched bees in greenhouses will see that they are neither confined by original instinct to special flowers, nor do they visit all flowers indifferently.
It would also appear that individual bees differ somewhat in their mode of treating flowers. Some Humble-bees suck the honey of the French bean and Scarlet runner in the legitimate manner, while others cut a hole in the tube and thus reach it, so to say, surreptitiously; and Dr. Ogle has observed that the same bee always proceeded in the same manner some always by the mouth of the flower, others always cutting a hole. He particularly mentions that this was the case with bees of one and the same species, and infers, therefore, that the different individuals differ from one another in their degrees of intelligence; these observations, though of course not conclusive, are interesting and suggestive.
Lastly, some insects confine themselves to particular flowers. Thus, according to H. Muller Andrena florea Halictoides Andrena hattorfiana Cilissa melanura Macropis labiata Osmia adunca Visits exclusively.
Bryonia dioica Species of Campanula Scabiosa arvensis. Lythrum Salicaria. Lysimachia vulgaris. Echium.
The arrangements to which I have hitherto called attention are for the most part of such a nature as to adapt the flowers to the visits of insects. There are others, however, of much interest which serve to protect them from unwelcome visitors, such as ants, who would rob them of their honey without fulfilling any useful purpose in return. Some plants are protected by downward pointing hairs, others by viscid glandular hairs, others by the extreme smoothness of their surface. In other cases the flower is closed by barriers, which only leave sufficient space for the slender proboscis of the bees, while others again, such as the Foxglove, are closed boxes which bees only are able to enter.
Another remarkable peculiarity of plants, which may I think possibly have reference to their relations with insects, is the habit of "sleeping," which characterises certain species.
Many flowers close their petals during rain, which is obviously an advantage, since it prevents the honey and pollen from being spoilt or washed away. Everybody, however, has observed that even in fine weather certain flowers close at particular hours. This habit of going to sleep is surely very curious. Why should flowers do so?
In animals we can understand it; they are tired and require rest. But why should flowers sleep? Why should some flowers do so, and not others? Moreover, different flowers keep different hours. The Daisy opens at sunrise and closes at sunset, whence its name "day's-eye." The Dandelion (Leontodon taraxacum) is said to open about seven and close about five; Armaria rubra to be open from nine to three;1 Nymphaea alba from about seven to four; the common Mouse-ear Hawkweed (Hieracium Piloselld) from eight to three; the Scarlet Pimpernel (Ana-gallis arvensis) to waken at seven and close soon after two; Tragopogon pratensis to open at four in the morning, and close just before twelve, whence its English name, "John go to bed at noon." Farmers' boys in some parts are said to regulate their dinner-time by it. Other flowers, on the contrary, open in the evening.1
Now, it is obvious that flowers which are fertilised by night-flying insects would derive no advantage from being open by day; and on the other hand, that those which are fertilised by bees would gain nothing by being open at night. Nay, it would be a distinct disadvantage, because it would render them liable to be robbed of their honey and pollen, by insects which are not capable of fertilising them. I would venture to suggest, then, that the closing of flowers may have reference to the habits of insects, and it may be observed also in support of this that wind-fertilised flowers do not sleep; and that some of those flowers which attract insects by smell, emit their scent at particular hours; thus, Hespeiris matronalis and Lychnis vespertina smell in the evening, and Orchis bifolia is particularly sweet at night.
1 In my own observations the opening and closing was more gradual . and more dependent on the weather than I should have expected from the statements quoted above.
Bees appear, moreover, to be skilful in adapting the hour of their visits to the habits of the plants. Thus M. Boissier tells us ("Les Nectaires," p. 166), that he observed some species of Sempervivum (S. tectorum, S. arachnoideum, S. montanum, S. rejiextim, and S. maximum) growing abundantly on rocks, which secreted honey in the morning only. These plants were much frequented by bees up to midday, but quite deserted in the afternoon. He has also observed that some bees which specially frequented Limes and a field of Clover (Trifolium repens), went to the former in the early morning, and did not commence visiting the clover until the dew was off. During the height of summer in Provence, the flowers, he tells us, secrete no honey in the heat of the day; and the bees also remain at home. Mr. Todd even assures us that at Blidah in Algeria the bees during summer do not work after eight in the morning.