The Naturalist on the Thames

by C. J. Cornish

Many of the flowers are not quite what their names imply. The true lilies are among the oldest of plants. But "water-lilies" are not lilies. They have been placed in order between the barberry and the poppy, because the seed-head of a water-lily is like the poppy fruit. The villarsia, which looks like a water-lily, is not related at all, while the buck-bean is not a bean, but akin to the gentians. Water-violet might be more properly called water-primrose, for it is closely related to the primrose, though its colour is certainly violet, and not pale yellow. By this time all the bladderworts have disappeared under water. In June in a pool near the inflow of the Thames at Day's Lock, opposite Dorchester, the fine leafless yellow spikes of flower were standing out of the water like orchids, while the bladders with their trapdoors were employed in catching and devouring small tadpoles. There is something quietly horrible about these carnivorous plants. Their bladders are far too small to take one in whole, but catch the unhappy infant tadpoles by their tails and hold them till they die from exhaustion.

The bank flora of the Thames is nearly all the same from Oxford to Hampton Court, made up of some score of very fine and striking flowers that grow from foot to crest on the wall of light marl that forms the bank. Constantly refreshed by the adjacent water, they flower and seed, seed and flower, and are haunted by bees and butterflies till the November frosts. The most decorative of all are the spikes of purple loose-strife. In autumn when most of the flowers are dead the tip of the leaf at the heads of the spikes turns as crimson as a flower. The other red flowers are the valerian, in masses of squashed strawberry, and the fig-wort, tall, square-stemmed, and set with small carmine knots of flower. In autumn these become brown seed crockets, and are most decorative. The fourth tall flower is the flea-bane, and the fifth the great willow-herb. The lesser plants are the small willow-herbs, whose late blossoms are almost carmine, the water-mints, with mauve-grey flowers, and the comfrey, both purple and white. The dewberry, a blue-coloured more luscious bramble fruit, and tiny wild roses, grow on the marl-face also. At its foot are the two most beautiful flowers, though not the most effective, the small yellow snapdragon, or toad-flax, and the forget-me-not. This blue of the forget-me-nots is as peculiar as it is beautiful. It is not a common blue by any means, any more than the azure of the chalk-blue butterflies is common among other insects. Colour is a very constant feature in certain groups of flowers. One of these includes the forget-me-nots, the borage, the alkanet, and the viper's bugloss, which keep up this blue as a family heirloom. Others of the tribe, like the comfrey, have it not, but those which possess it keep it pure.

The willows at this time are ready to shed their leaves at the slightest touch of frost. Yet these leaves are covered with the warts made by the saw-flies to deposit their eggs in. The male saw-fly of this species and some others is scarcely ever seen, though the female is so common. The creature stings the leaf, dropping into the wound a portion of formic acid, and then lays its egg. The stung leaf swells, and makes the protecting gall. It is difficult to say when "fly," in the fisherman's use of the term as the adult insect food of fish, may not appear on the water. Moths are out on snowy nights, as every collector knows, and on any mild winter day flies and gnats are seen by streams. In the warm, sunny days of late September, numbers of some species of ephemerae were seen on the sedges and willows, with black bodies and gauzy wings, which the dace and bleak were swallowing eagerly, in quite summer fashion. The water is now unusually clear, and as the fish come to sun themselves in the shallows every shoal can be seen.

Among the typical Thames-valley flowers, all of which would be the better for protection, are the very rare soldier orchis (Orchis Militaris) and the monkey orchis (Orchis Simia), the water-snowflake, the hottonia, or water-violet, the water-villarsia, more elegant even than the water-lilies, the flowering rush, with a crown of bright rose-pink flowers. The two orchids named are very interesting plants. Of the monkey orchis Mr. Claridge Druce says in his "Flora of Oxfordshire" that it has become exceedingly scarce, not so much from the depredations of collectors, but from the fondness of rabbits for it and the changes brought about by agriculture. The soldier orchis is very rare indeed; both are only found in a few woods in the Thames valley, and possibly in Kent. The bladderworts fade instantly, and are not much interfered with, and though the fritillaries are picked for market, the roots are not dug up because that would injure the meadow turf in which they grow, and business objections would be raised.

[INSECTS OF THE THAMES]

Except among the select few, generally either enthusiastic boys or London mechanics of an inquiring mind, who keep fresh-water aquariums and replenish them from ponds and brooks at "weekends," few persons outside the fancy either see or know much of the water insects, [1] or are aware, when floating on a summer day under the willows in a Thames backwater, of the near presence of thousands of aquatic creatures, swift, carnivorous, and pursuing, or feeding greedily on the plants in the water garden that floats below the boat, or weaving nests, tending eggs, or undergoing the most astonishing transitions of form and activity, on or below the surface. Many of them are perhaps better equipped for encountering all the chances of existence than any other creatures. They can swim, dive, and run below water, live on dry land, or fly in the air, and many are so hardy as to be almost proof against any degree of cold. The great carnivorous water-beetle, the dytiscus, after catching and eating other creatures all day, with two-minute intervals to come up, poke the tips of its wings out of the water and jam some air against its spiracles, before descending once more to its subaqueous hunting-grounds, will rise by night from the surface of the Thames, lift again those horny wing-cases, unfold a broad and beautiful pair of gauzy wings, and whirl off on a visit of love and adventure to some distant pond, on to which it descends like a bullet from the air above. When people are sitting in a greenhouse at night with no lamp lighted, talking or smoking, they sometimes hear a smash as if a pebble had been dropped on the glass from above. It is a dytiscus beetle, whose compound eyes have mistaken the shine of the glass in the moonlight for the gleam of a pond. At night some of the whirligig beetles, the shiny, bean-like creatures seen whirling in incessant circles in corners by the bank, make a quite audible and almost musical sound upon the water. The activity of many of the water insects is astonishing. Besides keeping in almost incessant motion, those which spend most of their time below water have generally to come up constantly to breathe. Such are the water-bugs, water-scorpions and stick insects, which, though slender as rushes, and with limbs like hairs, can catch and kill the fry of the smaller fishes. Most of these are like divers, who have to provide themselves with air to breathe, and work at double speed in addition.

If a group of whirligig beetles is disturbed, the whole party will dive like dabchicks, rising to the surface again when they feel the need for breathing-air again. The diving-bell spiders, which do not often frequent the main Thames stream, though they are commonly found in the ditches near it, gather air to use just as a soldier might draw water and dispose it about his person in water-bottles. They do this in two ways, one of which is characteristic of many of the creatures which live both in and out of the water as the spider does. The tail of the spider is covered with black, velvety hair. Putting its tail out of the water, it collects much air in the interstices of the velvet. It then descends, when all this air, drawn down beneath the surface, collects into a single bubble, covering its tail and breathing holes like a coat of quicksilver. This supply the spider uses up when at work below, until it dwindles to a single speck, when it once more ascends and collects a fresh store. The writer has seen one of these spiders spin so many webs across the stems of water plants in a limited space that not only the small water-shrimps and larvae, but even a young fish were entangled. The other and more artistic means of gathering air employed by the spider is to catch a bubble on the surface and swim down below with it. The bubble is then let go into a bell woven under some plant, into which many other bubbles have been drawn. In this diving-bell the eggs are laid and the young hatched, under the constant watch of the old spider. Few people care to take the trouble to gaze for any time into a shallow, still piece of water, in which the bottom is plainly discernible, and a crop of water-weeds makes a wall on either side of some central "well." If they do find some such pond near the Thames banks or a shallow backwater, they may see after a few minutes much that is new and suggestive of strange activities. Everything will be quiet and motionless at first, for water beasts are very suspicious of movement above them, and all sham dead, or lie quite still, and are strangely invisible. On the other hand, they have none of the power of remaining motionless for half-an-hour like land animals. Soon what look like sticks, but are caddis larva, begin to creep on the bottom. Then more brown objects, larvae of dragon-flies and water-beetles, detach themselves from the stems of the plants and cruise up and down seeking what they may devour. Other creatures feeding and swimming among or beneath the plants crawl out on to the upper surface, and the water-beetles come up to breathe, or to play upon the surface. One of the largest of these is a very fine black beetle, a vegetable-feeding creature. It is most interesting to see two of them--they generally live in pairs--browsing on one of the fern-like plants of the Thames. This plant has leaves like fern blades, each having in turn its own small spikelets. The big beetles work along the leaf like a cow in a cabbage yard, biting off, chewing, and swallowing each in succession, and leaving the stem perfectly bare. Sometimes it looks as if the two beetles were eating for a match, like the beef-eating contests held in country public-houses, in which the winner once boasted that he won easily "afore he came to vinegar."

The number of carnivorous creatures found in the water seems out of all proportion to the usual order of Nature. But this is perhaps because the minute, almost invisible creatures, or entomostraca, of which the rivers and ponds are full, and which are the main food of the smaller water carnivora, live mainly on decaying vegetable substance, which is practically converted and condensed into microscopical animals before these become in turn the food of others. It is as if all trees and grass on land were first eaten by locusts or white ants, and the locusts and white ants were then eaten by semi-carnivorous cows and sheep, which were in turn eaten by true carnivora. The water-weeds, both when living and decaying, are eaten by the entomostraca, the entomostraca are eaten by the larvae of insects, the perfect insects are eaten by the fish, and the fish are eaten by men, otters, and birds. Thus we eat the products of the water plants at four removes in a fish; while we eat that of the grass or turnips only in a secondary form in beef or mutton.

The water-shrimp is a very common crustacean in the small Thames tributaries, and valuable as fish food. It has a very rare subterranean cousin known as the well shrimp. A lady in the Isle of Wight, who in a moment of energy went to the pump to get some water to put flowers in, actually pumped up one of these subterranean shrimps into a glass bowl. The well was eighty feet deep. The shrimp was absolutely white, and probably blind.

Flesh-eating insects are fairly common on land; wasps will actually raid a butcher's shop, and carry off little red bits of meat, besides killing and eating flies, spiders, and larvae. Dragon-flies are the hawks of the insect world, and slay and devour wholesale, when in the air as well as when they are larvae on the water, though few persons actually witness their attacks on other creatures, owing to the swiftness of their flight. Some centipedes will attack other creatures with the ferocity of a bulldog. An encounter between one of the smaller centipedes and a worm is like a fight between a ferret and a snake, so frantic is the writhing of the worm, so determined the hold which the hard and shiny centipede maintains with its hooked jaws. But the ferocity and destroying appetite of some of the water creatures would be appalling were it not for their small size. The desire of killing and devouring appears in the most unexpected quarters, among creatures which no one would suspect of such intentions. Of two kinds of water snail found in the Thames, and among the commonest molluscs, one is a vegetable feeder. It is found living on water plants, the snails being of all sizes, from that of a mustard seed to a walnut. The other will feed not only on dead animal substances, but on living creatures, and is equipped with sharp teeth, which work like a saw. One of these kept in an aquarium fastened on to and slowly devoured a small frog confined in the same vessel. The large dytiscus beetle is the great enemy of small fish. If the salmon is ever restored to the Thames these creatures will be among the worst enemies of the fry, though in swift rivers they are not plentiful. Frank Buckland states that in Hollymount Pond they killed two thousand young salmon. One of these was put into a bowl with a dytiscus beetle, which, "pouncing upon him like a hawk upon an unsuspecting lark, drove its scythe-like horny jaws right into the back of the poor little fish. The little salmon, a plucky fellow, fought hard for his life, and swam round and round, up and down, hither and thither, trying to escape from this terrible murderer; but it was no use, he could not free himself from his grip; and while the poor little wretch was giving the last few flutterings of his tail, the water-beetle proceeded coolly to peck out his left eye, and to devour it at once." The larva not only of the carnivorous dytiscus but also of the vegetable-feeding water-beetle are ferocious and carnivorous, and deadly enemies of young fish and ova.