Page:The New International Encyclopædia 1st ed. v. 07.djvu/856

* FLOWERS AND INSECTS. 760 FLOWERS AND INSECTS. here again we have long, slender, beak-like mouth- parts adapted for probing flowers. The modifications of the maxillae (jaws) of cer- tain flower-visiting insects, adapting them in some - for playing the part of butterflies and bees, are remarkable. Leaf-feeding beetles, such as chafers and chrysomelids, do much harm by de- vouring petals or entire flowers, but there is no resulting modification. "A review," says Jluller, "of the mode of life of insects which visit flowers, and of the families to which they belong, shows continuous gradations from those which never visit flowers to those which seek them as a sec- ondary matter, and finally to those which en- tirely depend upon them." In the great group of longicorn beetles (Cerambycidse), in which the head is generally short, the jaws are directed downward, so they can use them in biting the bark of trees in order to oviposit in it. There is a group (Lepturidse) which frequents flowers. These have the head lengthened out in front, a neck-like constriction behind the eyes, and con- sequently the power to direct the mouth forward while the prothorax is elongated and narrowed in front; besides this, the lobes of each maxilla are furnished with a brush of hairs. All these departures from the normal type and customary habits are the result of a process of adaptation to a floral diet. Miiller attributes this to natural selection, but one will readily perceive that this view is not practical nor adequate. There may be another point of view. As this type of beetles multiplied and ordinary food became scarce, com- petition set in, necessities of existence drove t he insects to the unusual diet of pollen and honey, and probably the body became modified as the re- sult of constant effort in straining after the nec- tar at the bottom of flowers, and the creature became long-necked, long-headed, and its tongue- M W1I.1.A OF nkioi;natha. 1. Maxilla (entire), showing the prolonged galea. 2. En- larged view of biiHa! part, of maxilla, to show the taste- papillae (tp), and cups (to) on the galea (g&): n, nerve — a i. d.il nerve supplies eueh t asl e-pa pilla or CUp; /. lacinla: /-. palplfer; s, subgalea. :t. Part of end of galea, more enlarged to show the Imperfect segments ami the taste-organs, i Henslov. ) like maxilla especially adapted for brushing off nl i oiler-ting grains of pollen. The case reminds One of I lie probable series of causes which led to the formation of the long neck anil slender head and tongue of the gira lie Other beetles gather pollen, and their mouth- appendages are adapted in accordance with this habit, while among certain families (e.g. Mor- dellidae, CEdenrerida; ) all the species in a perfed state depend entirely on a floral diet. The most remarkable of all beetles adapted for sucking honey is the flower-visiting Nemognatha (which means 'thread-like jaws'), in which the galea of each maxilla is of enormous length, so that the two together form a rude sucking-tube, roughly comparable with the tongue of the butterflies. It is believed to be very sensitive, as it contains many taste-cups. Here we see carried out almost to excess the idea of a tongue adapted for prob- ing deep corollas. It is a case of convergence, where the action of similar efforts and mechanical strains have gradually resulted in structures of the same form in insects belonging to entirely different orders. Flies. The majority of the flies (Diptera) re- sort to flowers for the little food they require in the imago state. And here the mouth-parts are very different in structure from those of bit- ing insects, the long proboscis being a modifica- tion of a portion of the labium, representing the tongue or "lingua' of other insects. The beauti- ful yellow, wasp-like drone-flies (Syrphidse), so abundant about flowers and so important as fer- tilizers, depend mainly or exclusively on a floral diet; and here, as Miiller states, "are found the most perfect adaptations to a diet alternately of pollen and honey." The complicated proboscis ends in two broad flaps. These flaps are "admi- rably adapted for seizing the pollen, for grinding it down, and for passing it backward, the ap- posed surfaces of the two Haps being closely set with parallel ridges of chitin, by which the pollen- grains are easily held fast and shoved into the entrance of the groove. Diptera, like the house and allied flies (Muscida?, also the Stratiomyi- dse), visit flowers to obtain both pollen and honey. These flaps are wanting in other flies, as the mosquito, and in the Bombyliidse, which have enormously long tongues, as well as in other families (Empida? and Conopida?). and these flies visit flowers, probing them for the honey alone. Now, in these flies the head itself is not espe- cially modified, but in Rhingia the head is devel- oped into a long snout, the tongue being longer than the whole body. This fly (one of the Syr- phida?) is remarkably intelligent, probing the deeply hidden nectary of the iris and many other flowers. The species of Empis carry their long, thin, straight proboscis directed downward; hence they chiefly resort to erect flowers, into which they can plunge their proboscis vertically. In all these Hies there is great variation in the shape and degree of specialization of the mouth- parts, these being in intimate relation with the Jiahits of these highly specialized insects. Hymenopteba. Still better adapted than the flies arc the wasps, anil especially the bees, which rely almost exclusively on a floral diet, and are most important as fertilizers of flowers. In bees (q.V.) the mouth-parts are wonderfully adapted for probing flowers, the maxilla being specialized in a variety of ways, while with its stout mandi- bles the bumblebee can cut a hole through the corolla of Salvia or Wistaria, without taking the trouble, as tin. honey bee does, to seek out the nectary. Besides the mouth parts, the hairy legs. especially those of the hinder pair, arc so modified as to form pollen-baskets (corbicula), in which the pollen is heaped, or the bristly hairs on the