The third species—the Great English Sundew (D. anglica)—is still rarer. Its leaves are still longer and narrower, being sometimes an inch or more in length, and more erect; and the flower-stalk sometimes attains a length of eight inches.
The carnivorous habits of these plants are very similar to those of the Butterworts, but the movements connected with the capture of the prey are more marked in the red filaments which cover the upper surface of the leaves than in the leaves themselves. Those filaments which are situated on the margin of the leaf are longest, and spread outwards, while the others are erect and decrease in length from the edge towards the middle.
Each filament is swollen at its extremity, and supports an enticing globule of glistening fluid which it secretes, for the enlarged extremity is really a minute gland. The fluid, though quite clear, is so viscid that it can be drawn out into threads, and it serves a purpose similar to that of the sticky globules on the spiral thread of a spider's web.
If some grains of sand or other inorganic material be sprinkled on the leaf, the sticky secretion of the glands is appreciably increased, and at the same time assumes an acid character; but it contains no digestive ferment, nor do the filaments change their position to any considerable extent. When, however, a small insect alights on the leaf, attracted by the glistening drops which are probably mistaken for nectar, the secretion not only increases and becomes acid, but a digestive ferment is produced, and the little creature is soon besmeared with the fluid, its condition becoming more and more hopeless through its struggles, till at last further movements are impossible and it dies of suffocation.
A few minutes later the filaments of the leaf immediately around the insect begin to bend towards it, and others a little farther off soon partake in the movement, which may finally extend more or less to all the filaments of the leaf, and thus a large number of glands are brought in contact with the prey. The process of digestion now goes on, and, in a day or two, all the digestible portions of the insect are dissolved and absorbed, and the filaments that were concerned in the work have resumed their original position, leaving the indigestible portions to dry and to be eventually blown away.
The principal food of the Sundews consists of small insects such as ants, midges, flies, small butterflies and moths, caddis-flies, and even small species of dragon-flies. Some of these, more particularly the long-bodied dragon-flies, the smallest of which are over an inch in length, are much too large to be caught and devoured by a single leaf; and in this case it is not at all uncommon for two or more leaves to be concerned in the capture and digestion of a single insect, each one converging its filaments towards the part of the body within its reach, and each one digesting and absorbing the portion against which it can apply its glands.
Insects, however, do not constitute the sole food of these plants, for small worms, spiders, centipedes, &c., are caught and digested in the manner described; and the plants may also be fed artificially on small pieces of meat or other nitrogenous substances, which give rise to the same processes and movements as we have observed in connection with the natural mode of feeding.