CHAPTER XXI.

PLANTS WHICH EAT INSECTS

As a rule, plants are the sufferers and are eaten by animals, but there are cases known in which this state of things is reversed; the plants catch and devour the tinier animals and small insects such as flies. But, you may ask, how can they do that, for the insects move so quickly, and the plants are fastened by their roots to one spot. Just as a spider builds a web and then waits quietly beside it till the flies are caught, so the plants build traps which catch the unwary insects. There are not very many plants growing wild in England which do this, but there are one or two that you might be able to find.

There is the sundew, which grows among bog-moss in wet, swampy places at the edges of lakes, or on the wet patches on hillsides. It is fairly common in such places, a little distance from big towns, but it does not like smoke, so that it will not live within a few miles of London, Manchester, or any big smoky town. It is a small plant with round, reddish-coloured leaves, covered over with little fingers or tentacles each with a sparkling drop of sticky moisture at the end, so that even in the heat of the day when all the dew is dried up, the whole plant looks as though it were spangled with tiny dew-drops. Perhaps it is this cool, sparkling appearance which attracts the insects to it, but when once a fly alights on one of the leaves, its fate is sealed. The tentacles with their sticky tips bend over one by one till the fly is quite covered in by them and cannot get away. It dies, and is digested by the juices given out by the leaf, which are very much like the digestive juices of animals.

You can watch the movement of the tentacles very well if you drop a minute piece of meat or white of egg on to the leaf. They will close over it one by one till it is quite shut in, and when the egg is all digested, they slowly open out again. The time that this takes depends a little on the health of the plant and the time of the year, but generally all the tentacles are bent over in a few minutes. The digestion takes longer, of course, at least several hours and often more, partly depending on the size and nature of the piece of food. The sundew leaves contain chlorophyll and do some of the usual work of leaves, but the plant gets much of its nourishment from the insects it catches.

In the butterwort there is a different arrangement for catching its prey. You will find its little clusters of broad, spoon-shaped, yellowish-green leaves growing in marshy places and beside streams in hilly districts. In the spring one or two lilac flowers on long stalks come up from the centre of the group of leaves. The leaves of this plant also act as insect traps; they are covered with little sticky glands, and when an insect settles on them, the edge rolls over and shuts it in, keeping it there till the juices given out by the glands have digested all that is worth digesting, when the leaf unrolls again, and the remains of the feast are washed away by the rain.

There is one more animal eater which you must try to see, which grows in the water of slow-running streams and in ponds. It is the bladderwort, on which we find very many tiny bladder-like structures on the finely divided leaves under the water. The bladders are built on something of the same plan as a lobster pot, with bristly hairs pointing into the entrance, across which there is a little flap, which makes it quite easy for the very minute animals living in such abundance in the water, to swim ~into~ the bladder opening, but extremely difficult or almost impossible for them to swim out again (~see~ fig. 114). So there they must finally die, and their nourishing juices are absorbed by little compound hairs, many of which are developed on the inside of the bladder.

In the tropical countries there are many kinds of “pitcher plants” with wonderful soup-kettle-like pitchers which catch insects. You may be able to see these plants in a big greenhouse, and should certainly find them in every botanical garden. Notice how large the pitchers are, and that they are really modified leaves which have become different from the other leaves of the plant because of their special work. They generally contain a considerable quantity of water as well as the flies they have caught, and are really “stock-pots” which keep the plant supplied with nourishing, ready-made food in addition to the food which it builds for itself in the green leaves.

Though these plants have specialised themselves to catch and use animal food, still there are not very many plants that do so, and the old fairy tales about trees with branches which caught men and devoured them, as a sea-anemone catches and devours its food, are only fairy tales, because no such plants exist.