James G. (James George) Needham.

The life of inland waters; an elementary text book of fresh-water biology for students online

. (page 21 of 26)
Online LibraryJames G. (James George) NeedhamThe life of inland waters; an elementary text book of fresh-water biology for students → online text (page 21 of 26)
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of more or less limpet-shaped invertebrates.

The animals of lotic societies are mainly small inver-
tebrates. There are fishes, indeed, like the darters that
live in the beds of rapid streams. These lie on the
bottom where the current slackens, lightly poised on
their large pectoral fins, or rest in the lee of stones,
darting from one shelter to another. It is only a few


364 Aquatic Societies

lesser animals, of highly adapted form and habits, that
are able to dwell constantly in the rush of waters.

These lesser animals may be roughly divided into two
categories according to the sources of their principal
food supply:

1 . Plancton gathering forms, that are equipped with
an apparatus for straining minute organisms out of the
open current.

2. Ordinary forms that gather home-grown food
about their dwelling places.

I. Plancton Gatherers. These are they that live
mainly on imported food, which by means of nets or
baskets or strainers they gather out of the passing
current. These are the most typical of lotic organisms,
for they must needs live on the exposed surfaces that
are washed by the current. They dwell on the bare
rock ledge, over which the water glides swiftly, or on the
top of the boulders in the stream bed, or on the exposed
side of the wave- washed pier. They are few in kinds,
and very diverse in form, and show many signs of
independent adaptation to life in such situations.
Among them are four that occur abundantly in the
Ithaca fauna. These four and their mode of attach-
ment and of plancton gathering are illustrated in the
accompanying diagram. The fly larva, Simulium,
adheres by a caudal sucker, gathers plancton by means
of a pair of fans placed beside its mouth, while its body
dangles head downward in the stream. The larva of
the caddis-fly, Hydropsy che, lives in a tube and con-
structs a net of silk that strains organisms out of the
water running through it. The caddis-worm, Brachy-
centrus, attaches the front end of its case firmly to the
top of a boulder in the stream bed, and then spreads its
bristle-fringed middle and hind feet widely to gather in
organisms that may be adrift in the passing water.

Plancton Gatherers


The nymph of the "Howdy" Mayfly, Chirotenetes, fixes
itself firmly with the stout claws of its middle and hind
feet clutching a support, and extends its long fore feet
with their paired fringes of long hair outspread like a
basket to receive what booty the current may bring.
These four are so different they are better considered
a little further separately.

The larva of Simulium (the black-fly, or buffalo gnat)
perhaps the most wide-spread and characteristic animal



FIG. 217. Plancton-gathering insects
of the rapids. The arrow indicates
direction of stream-flow.

of running water, is unique in form and in habits. It
hangs on by means of a powerful sucker that is located
near the caudal end of its soft and pliant bag-shaped
body. But it may also attach itself to the stones by a
silken thread spun from its mouth: and if it then
loosens its sucker, it will dangle at the end of the thread,
head upstream. By means of these two attachments,
it may travel from place to place without being washed
away, but in the swiftest water, it can make only short
moves sidewise. It travels by loopings of its body, like
a leech. So it shifts its location with changes of water
level, always seeking the most exposed ledges which a
thin sheet of water pours over. There it gathers in
companies, so closely placed side by side as to form
great black patches on the stones.

366 Aquatic Societies

There is little movement from place to place. The
larvae hang at full stretch, their pliant bodies swaying
with little oscillations of the current, their fans out-
spread, straining what the passing stream affords.
Each of these fans is composed of several dozen slender
rays, each one of which is toothed along one margin
like a comb of microscopic fineness, and all have a
parallel curvature like the fingers of an old-fashioned
reaper's cradle. They are efficient strainers.

When grown the larva spins its half cornucopia-
shaped straw-yellow cocoon on the vertical face of a
ledge where the water will fall across its upturned open
end, then transforms to a pupa inside. The pupa bears
on the prothorax a pair of long, conspicuous, many
branched respiratory horns, or "tube gills" (see fig. 171
on p. 280).

The eggs are laid at the edge of the swiftly flowing
water on any solid support, on the narrow strip that is
kept wet, and, by oscillations of the current occasionally

Hydropsyche, the seine making caddis-worm, lives in
sheltering tubes of silk, spun from its own silk glands,
fixed in position on the surface of a stone (oftenest in
some crevice) , and covered on the outside with attached
sticks or broken fragments of leaves or stones. Always
one end of the tube is exposed to the current, and at
this end, the larva reaches out to forage. Here it con-
structs its net of cross woven threads of fine silk. The
net is a more or less funnel-shaped extension of silk from
the front of the dwelling- tube. The opening is directed
upstream, so that the current keeps it fully distended.
The semi- circular front margin is held in place by
means of extra stay lines of silk. The mesh is rather
open on the sides, but on the bottom there is usually a
small feeding surface that is much more closely woven.

Plancton Gatherers 367

The larva lies in its tube in readiness to seize anything
the current may throw down upon its feeding surface
or entangle in the sides of its net. The whole net is so
delicate that it collapses on removal from the water.
To see it in action, it is best examined through a
" water-glass."*

Brachycentrus, the "Cubist" caddis-worm, is re-
stricted in habitat to spring-fed streams flowing
through upland bogs. It constructs a beautiful case
that is square in cross-section. Each side is covered
with a single row of sticks (bits of leaf stalks, grass
stems, etc.) placed crosswise. The larva fastens its
case by a stout silken attachment to the top of some
current-swept boulder and then rests with legs out-
spread as indicated in figure 217 in a receptive atti-
tude, waiting for whatever organic materials the current
may bring within its grasp.

The Nymph of Chirotenetes, the "Howdy" Mayfly, lives
on the rock ledge or where the water sweeps among the
stones. Its body is of the stream-line form discussed
in the last chapter the form best adapted to diminish-
ing resistance to the passage of water, as well when at
rest as when swimming. The nymph sits firmly on its
middle and hind feet. Holding its front feet forward, it
allows the current to spread out their strainer-like
fringes of long hairs. These retain whatever food is
swept against them, and the mouth of the nymph is
conveniently near at hand. It uses its feet for stand-
ing but moves from place to place by means of swift
strokes of its finely developed tail fin, supplemented by
synchronous backward strokes of its strong tracheal gill
covers. It has almost the agility and swiftness of a

*A "water-glass" is any vessel having opaque sides and a glass bottom, of
convenient size for use. An ordinary galvanized water pail with its bottom
replaced by a circular glass plate set nearly flush, is excellent.

368 Aquatic Societies

2. Ordinary Foragers. These are the members of
lotic societies that lack such specialized means of
gathering food from the passing current, and that forage
by more ordinary methods. They live for the most
part on the sides of stones and underneath them, and
not on their upper surfaces. These also live where the
water runs swiftly, and, for the most part, out of the
reach of those fishes that invade the rapids. There are
two principal categories among them: a. Free-living
forms that are more or less flattened or limpet -shaped.
b. Shelter-building forms, that are in shape of bo^y
more like the ordinary members of their respective


The limpet-shaped forms are members of several
orders of insects, worms and snails. Their flattened
form and appressed edges are doubtless adaptations to
life in currents. They adhere closely, and are on
account of their form, less likely to be washed away;
the current presses them against the substratum.

Not the most limpet -like but yet the best adapted
for hanging on to bare stones in torrents is the curious
larva of the net-veined midge, Blepharocera (see fig. 159
on p. 259), an inhabitant only of clear and rapid streams.
The depressed body of this curious little animal is
equipped with a row of half a dozen ventral suckers,
each of which is capable of powerful and independent
attachment to the stone. So important have these
suckers become that the major divisions of the body
conform to them and not to the original body segments.
On these suckers, used as feet, the larva walks over the
stones under the swiftest water, foraging in safety where
no enemy may follow.

Most limpet-like in form of all is the larva of the
Parnid beetle, Psephenus, commonly known as the

Ordinary Foragers


" water-penny " (see fig. 160 on p. 260). It is nearly
circular and very flat with flaring margins that fit down
closely to the stone. It adheres closely and is easiest
picked up by first slipping the edge of a knife under it.
Viewed from above, it has little likeness to an ordinary
beetle larvae, but removed from the stone and over-
turned, one sees under the shell a free head, a thorax
with three short legs, an
abdomen and some minute
soft white segmentally
arranged tracheal gills on
each side.

Other insect larvae that
have taken on a more or
less limpet -like form, are
the nymphs of certain May-
flies and of many stoneflies
(fig. in on p. 204). The
body is strongly depressed.
The lateral margins of the
head and thorax are ex-
tended to rest down on the
supporting surface. The
legs are broadened and are
laid down flat so as to
offer less resistance to the
currents, and stout grap-
pling claws are developed
upon all the feet. Such is
Heptagenia whose nymphs

FIG. 218. The nymph of a may-
fly (Heptagenia) from the

rapids, snowing depressed form

of the body and legs.
(Photo by Anna H. Morgan.)

abound in every riffle and

on every rocky shore.

One may hardly lift a stone from swift water and

invert and examine it without seeing them run with

sidelong gait across its surface, outspread flat, and

when at rest appearing as if engraven on the stone.


Aquatic Societies

The head is so flat and flaring that the eyes appear
dorsal in position instead of lateral as in pond-dwelling
Mayfly nymphs.

A more remarkable form is the torrent-inhabiting
nymph of Rithrogena whose gills are involved in
the flattening process. They also are flattened and
extended laterally and rest against the stone. But,

FIG. 219. Parallel development of limpet-like form of body-
in two mayflies. Right, the nymph of Ephemerella doddsi;
A, the overturned abdomen. Left, the nymph of Rithro-
gena mimus; B, the overturned abdomen ; C, the foremost
gill ; D, the second gill. (Courtesy of the Utah Agricultural
Experiment Station).

most remarkable of all, the anterior pair is deflected
forward and the posterior pair, backward, to meet on
the median line beneath the body, and both are
enlarged and margined; By the close overlapping
of all the gills of the entire series there is formed a large
oval attachment-disc of singularly limpet-like form.

A similar flat attachment-disc is formed on the
ventral side of the mayfly nymph shown in figure 219,

Shelter -building Forms 371

but on a wholly different plan. The gills are not
involved in the disc, but instead the body itself is
flattened and shaped to an oval form underneath, and
fringed with close set hairs.

There is in the mayflies a rather close correlation
between the degree of flattening of the body and the
rate of flow of the water inhabited. It is well illus-
trated by the allies of Heptagenia; also by those of
Ephemerella, among which occur swift -water forms.
Epeorus, Iron and Rithrogena form an adaptive series.
Among the Parnid beetles, Elmis (fig. 2i4b), Dryops
and Psephenus (fig. 160) form a parallel series.

There are snails that dwell in the rapids. The most
limpet-shaped of these is An cylus (fig. 160 on page 260)
whose widely open and flaring shell has in it only a
suggestion of a spiral. Certain other snails (such as
Goniobasis livescens) are of the ordinary form and are
able to maintain themselves on the stones by means of
a very stout muscular closely-adherent foot. Simi-
larly, a number of flatworms, that
adhere closely are found creeping
in the rapids.

Shelter-building foragers are num-
erous in individuals but few in
kinds. One tube-dweller, Hy-
dropsy che, is a planet on gatherer
and has been already discussed.
There are other shelter building
caddis-worms living among stones
in running water. Ryacophila FIG. 220. TWO pupal
builds at close of larval life a barri- cases of the caddis-fly,
cade of stones as shown in the fig. fS^^**^
125 on page 217, and shuts itself in
and spins about itself a brownish parchment-like cocoon
of the form shown in the accompanying figure. Heli-
copsyche constructs a spirally coiled case that is


Aquatic Societies

strikingly like a snail shell, and fastens it down closely
in the shallow crevices of stones on exposed surfaces.

FIG. 221. The spirally coiled cases of the
caddis-worm, Helicopsyche.

A number of other caddis-worms build portable cases
of sand and stones. Those of Goera (fig. 222) are
heavily ballasted by means of stones attached at the
sides with silk. These lie down flat against the bottom

and doubtless serve the

double purpose of de-
flecting the current and
preventing the case from
being washed away.

The tubes of the midges
are here made of less
soft and flocculent ma-
terials than in still
waters. Tanytarsus
makes an especially
tough case of a pale
brownish color, like dried
grass. It is of tapering
form, and easily recog-
nized by the three stay
lines that run out from
the open forward end.

FIG. 222 . Stone-ballasted cases of ^ Small greenish ydlow
caddis-worms of the genus Gcera. larva With rather long


Limpet-shaped Shelters


antennae lives within, and protrudes its pliant length

in foraging on the algal herbage that grows about its

front door. And

there are many

other lesser

midges whose

larvae dwell in

silt - covered

tubes on rocks

in the rapids.

Of ten they occur

so commonly as ,

- FIG. 223. Larval cases of the midge, Tanytarsus,

tO almost COVer attached to a stone in running water.

the surface.

Shelters also limpet-shaped It should be noted in
passing that this flattened form, which is characteristic
of so many members of lotic society, is characteristic
not only of the living animals but also of their shelters.
The tarpaulin-like web of the moth Elophila fulicalis
is flat, and the pupal shelter is quite limpet-shaped.
The case of Leptocerus ancylus is widely cornucopia-
shaped, its mouth fitted to the stone. The coiled
case of Helicopsyche is a very broad spiral, closely

FIG. 224. The maxilla of a mayfly, Ameletus ludens,
showing diatom rake.


Aquatic Societies

attached in the hollows of stones and crevices of rock
ledges. The case of the caddis-worm, Ithytrichia, (fig.
162 on p. 262) is broadly depressed.

Thus the impress of environment is seen not only
in the form of a living animal but also in that of the
non-living shelter that it builds. In this there is a
parallel of form in the secreted shell on the back of the
snail, Ancylus, and manufactured shell on the back of
the caddis- worm, Helicopsyche. One would have to
search widely to find better examples of the effects of
environment in molding to a common form these
representatives of many groups of very diverse struc-
tural types. Two of them, at least, were sufficiently
like lotic mollusca to have deceived their original
describers. Psephenus was first described as a limpet
and Helicopsyche as a snail.

Foraging habits The food of the herbivores in lotic
societies is algae. There are none of the higher plants

present, save a few
mosses of rather local
distribution. It is not
surprising therefore
that the food gather-
ing apparatus of these
forms should present
special adaptative
peculiarities. The
mouth-parts of may-
flies and of midges
show much develop-
ment of diatom rakes
and scrapers. For
scraping backward
the labrum is often

used. In the net-spinning caddis-worms it is bordered
on either side by a stiff brush of bristles, and in midge

FIG. 225. The sheltering tubes of
midge larvae. Photographed under
running water on the rocky bed of a

Foraging Habits


larvae there is developed both before and behind its
border a considerable array of combs and rakers. In
use the head is thrust forward, and these are dragged
backward across the surface that supports the growth
of diatoms and other algae.

The principal carnivores of the rapids are the nymphs
of stoneflies (see fig. HI on p. 204) and a few small
vertebrates. Among the latter are the insect-eating
brook salamander, Spelerpes, and a number of small
fishes, such as darters, dace and minnows.


Aquatic Societies


From the senior author's Report on a Biological Survey of Lake George
Courtesy of the New York State Conservation Commission


The Shoreward

The Openwafer &ssociat/or?.


May fry Mft/fe C/0m.

/>7ayf/y Cb&isf/y




ARDLY any native
species found by the
white man in America
had done so much to
alter and improve its
environment as had the
American beaver. Cer-
tainly the red man had
done less. Thousands
of acres of fertile valley
land now tilled by Amer-
ican plowmen was
___^ levelled up behind
beaver dams. These followed one another in close
succession in the valley of many a woodland stream.
The wash from the hills settled in their basins. As
they were filled, dams were built higher, and thus the
rich soil grew deeper.

The beaver was a builder of ponds. His only method
was by damming gentle streams. He cut down trees
with his great chisel-like teeth, trees often six, eight, or
ten inches in diameter. He cut off their boughs and



Inland Water Culture

drew them to the place where a dam was to be con-
structed. He piled them as a framework for a dam,
weighted them in position with stones, filled the inter-
stices with trash and leafage and covered the water
side over completely with mud, making it impervious.
And when the water had risen behind it he built him a
dome-shaped house on the edge of the pond thus
created, having passageways opening beneath the
water, and he plastered it over with mud. When
marsh plants grew about the edges of the lands he had
thus inundated, he cut channels through them for easy
passage to his favorite feeding grounds. His staple
food was the bark of aspens and birches that grew
thickly near at hand, but this he varied with succulent
shoots and tubers of aquatics. These nature planted
for him, as soon as he had prepared his water-garden.
This was aboriginal water culture.

FIG. 226. An aboriginal water-garden. A beaver dam and pond. (From Morgan.)


ERTILITY dwells at the
water side, where the
essential conditions for
growth m o i s t u r e ,
warmth, air and light
abound. There Nature's
crops are never failing.
They are abundant crops
compared with which the
herbage of the uplands
appear thin and scatter-
ing . If they are not our
crops, that is not Nature's
fault but our own. We
have given all our toil and care to the cultivation of the
products of the land, and have left the waters to pro-
duce what they might, often in the face of neglect and

Time was when the waters furnished to man the most
dependable part of his livelihood fish and oysters and
edible roots and excellent furs. That was before the
days of agriculture. Primitive man, while gathering
his fruit and roots and grains from the wild, saw the
supply failing and planted a garden to increase his
sustenance. Had he by like means endeavored to
supplement his stores of water products, we might now
have had a water culture, comparable with agriculture.
A number of native water plants furnished food to
the red men in America. One of these, the wild rice



Inland Water Culture

(fig. 227), ^ is ob-

tainable in our


own markets in

very limited

quantity and at

fancy prices : it

grows as a wild

plant still. The

Indian ate both


the nut-like seeds



and the stocks of


the wild lotus ;

* . V


also the tubers of


the arrowhead,


the stocks of the


arrow- arum, the

enormous rhizo-


i i *

mes of the spat-


X*. . t\*~^'

terdock, the suc-



culent shoots of

'f- -1 y~

P r^i^/ '

the cat- tail, and

^ "7 ! <;

^ v M '^ V /

other rather


^ /

coarse and watery


wild plant pro-

/& i



ducts, that we
esteem better


food for muskrats


than for men.



The starch-filled


tubers of the sago


pondweed (fig.


228) are choice


food for water-

fowl, and if ob-

PIG. 227. A flower-cluster of wild rice, fertile tainable in Suffi-

above, staminate below. Little brown syrphus cient nuantitv
flies of the genus Platypeza cling to the stem- ' ., - iT 1*1
inate blossoms. Would probably

Water Crops

be prized by men, for when cooked they are both pleas-
ing in appearance and very palatable.

A number of rushes of different sorts were in aborigi-
nal times used for coarse weaving of mats, etc.; and
one of these, the narrow-leaved cat-tail, we have of late
begun to use in new ways; in paper making and in

FIG. 228. Tubers of the sago pond weed.
Potamogeton pectinatus.

cooperage. The initial cut on the preceding page shows
a field of cat-tail carefully cut and shocked for use in the
calking of barrels that are to hold watery liquids. The
leaves are placed singly between the staves of the
barrels, where they swell when wet, packing the joints

It may be that none of these plants will ever be cul-
tivated. Some are abundant enough for present needs

382 Inland Water Culture

without it. Wild rice is but another cereal grain, tho
an excellent one. We already have garden roots in
great variety of sorts that we prize more highly than
we do these wild aquatics. The white water lily will
be cultivated in the future for its beautiful flowers
rather than for its edible tubers.

FIG. 229. The white water lily, Castalia odorata.

The animal products of the water are more important.
Aquatic molluscs, crustaceans, and vertebrates have
ever furnished staple foods. Tho fresh water molluscs
are no longer eaten, immense accumulations of their
shells along some of our inland waterways bear silent
testimony to the extent to which they were once con-
sumed by the aborigines. Their shells also served
other primeval uses, as cups and as scrapers. In our
own day a new and important use has been found for
them in the manufacture of pearl buttons and orna-



ments. They make the best of buttons, neat and dura-
ble and beautiful, a great improvement over the buttons
of wood and metal formerly in use. The annual
product of pearl buttons from this source is now worth
many millions of dollars. It is all derived from wild

FIG. 230. Valve of a mussel shell, with "blanks" cut from it,
in process of manufacture into pearl buttons.

mussels ;

the method in use is exploitation, not hus-

Fish The great staple food product of the water is
fish. In our day frogs are used but locally and fresh
water crustaceans and other animals, hardly at all;
but fishes are used everywhere. They have been a
staple food from the beginning of human history, and
probably will be to the end. Hence it is that inland

384 Inland Water Culture

water culture means to a large extent the raising of

Fish culture* in America is in a very backward state
as compared with animal husbandry in other lines.

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Online LibraryJames G. (James George) NeedhamThe life of inland waters; an elementary text book of fresh-water biology for students → online text (page 21 of 26)