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although not all of them lay their eggs around circular holes in
water-lily leaves, it appears that at least one of the rather widely
distributed species does have this habit. The extent of this
egg-laying interrelation of the two groups of insects is a problem
for the future.

Description, — The eggs are elliptical, smooth, slightly com-
pressed, and constant in size. When first hatched, the max-
imum dimensions are 0.396 mm. and 0.549 mm. The development
of the egg is accompanied by an increase in size so that just
before hatching the dimensions are 0.450 mm, and 0.648 mm.
Of the considerable number of measurements made, none
varied more than 0.03 mm. and even this variation was excep-
tional. It will be noticed that measurements of the egg made



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164 Annals Entomological Society of America [Vol. IX,

previous to the time of hatching agree quite closely with those
reported by Forbes ('10, p. 221). Apparently his measurements
were made on eggs which were well advanced in development.
Development, — The egg period was found to be about eleven
days, a result which agrees closely with that reported by
Forbes. When first laid, the eggs are yellowish, having about
the same color as the lower surface of the yellow water-lily leaf.
They are also slightly translutent. As development goes on
they become darker and proportionately more conspicuous on
the leaf. During the first 2-4 days following oviposition, little
if any change is apparent but subsequently internal differentia-
tion becomes noticeable. The eggs develop uniformly and
usually after a lapse of 3-5 days each begins to show a dark
band within, shaped somewhat like the letter J. The position
of this dark band is constant, the more curved end being in that
extremity of the egg remote from the margin of the hole in the
leaf. This band gradually becomes more conspicuous, ulti-
mately revealing itself as the developing body of the larva.
The triangular, chitinized pieces of the epicranium begin to
appear at the end of the fifth day and it was noted that they
develop in that end of the dark band nearest the margin of the
leaf puncture, showing that there is a definite orientation of the
egg and that the head of the larva develops at the less curved
end of the band. At the close of the eighth day, the larva is
quite distinct and occupies practically all of the space within
the egg. At the end of about ten days, the egg has lost all of
the original yellow appearance and the shell has become trans-
parent. The tiny caterpillar can be easily examined and it
begins to show movements within the egg. The primary regions
of the body are now distinct (Fig. 4), the epicranium and the
tips of the mouth parts are dark brown, the fronto-clypeal and
the occipital regions are light yellow in appearance, and the
chitinized, dark brown prothoracic shield and the dark bands in
the regions of the intersegmental grooves are distinctly visible
through the egg shell. In the eggs studied in this connection,
the dark color appeared first in the ocelli and on the dorsal
margins of the intersegmental grooves, later in the head and
prothoracic shield. The larva is doubled upon itself with the
caudal end extending around and beyond the head.



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1916] Biology of Aquatic Lepidoptera 165

Hatching. — In almost every case, the entire egg mass hatched
at about the same time. Occasionally, a few eggs lagged behind
but they hatched not later than five hours after the main group
of caterpillars had emerged. The first observed manifestations
of the hatching process were motions of the larva within the
egg, consisting of a series of body contractions and expansions
combined with movements of the head. The mandibles were
also in active motion. Apparently, the combined action of the
mandibles and the body movements were responsible for the
breaking of the egg shell. In the egg masses under observation,
the movements of the larvae preliminary to hatching began
from four to six hours before the final escape. The larva
emerged from one end of the egg, escaped quickly, and assumed
an active habit. In egg masses deposited under natural condi-
tions, the number of imperfect eggs was very small, not
exceeding three per cent.

The dates of collection of egg masses varied from July 10 to
August 20. Possibly, differences of seasons have some influence
on the egg-laying period since in 1913 numerous egg masses
were found as late as August 20, while during the preceding
summer none were found later than July 30.

The Larva (PL VII, Figs. 1-3).

First Instar. — The first instar has been briefly described by

Forbes ('10, p. 221) as follows: ''Stage I { )

Slightly larger than N. gyralis? described below, with propor-
tionately much larger anal setae, without trace of gills. Head
nearly .3 mm.; length of large anal setae 1 mm." A careftd
study of this instar has made it possible to extend the
description.

The larva, in this instar (Fig. 1), is light yellowish brown in
general appearance. The body is elongate, subcylindrical, and
tapers very slightly caudad. Body length of newly hatched
larvae varied from 1.26 to 1.5 mm. The maximum diameter is
in the region of the prothorax where it is about 0.32 mm. The
main divisions of the body and the intersegmental grooves are
distinctly marked. Duration of first instar in specimens reared
in aquaria, about 7 days.

Head approximately 0.3 mm. in width, smooth, shining, and
dark yellowish brown. Epicranial suture distinct. Front,
clypeus and labrum light yellow. Labrum emarginate, setose.



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166 Annals Entomological Society of America [Vol. IX,

Mandibles toothed, tips blackish. Labial palpi distinct,
penultimate segment truncate-conic, ultimate segment smaller
and cylindrical, not more than twice as long as thick, ter-
minating distad in three short, stout spines. Maxillary palpi
minute and inconspicuous, terminating in three minute articles.
Antennae distinct, basal joint truncate-conic, second segment
slender, cylindrical, about three times as long as thick; distal
•extremity with an apical seta nearly twice as long as segment
bearing it, and four minute articles, one of which bears a short
seta. Ocelli five, arranged in semicircle just caudad of base of
each antenna; dark area in connection with each group. One
pair of setae on epicranium near mid-dorsal line; a similar pair
near mesal margins of ocelli groups; two strong setae on each
lateral surface of head near ocelli.

Thoracic segments very finely granulose. Cervical shield
broad, black in color, strongly chitinized, smooth, widest at
mid-dorsal region; margins regular, anterior margin very
slightly conate, posterior margin slightly convex; covers greater
part of dorsal surface of prothorax. Meso- and metathorax
without traces of black, not strongly chitinized; color uni-
formly yellowish. Legs similar in size and color, each ending in
a single, strong curved claw. Each thoracic segment with three
pairs of well-developed setae on lateral and dorso-lateral surfaces.

Cephalic margin of abdominal segments I-VIII bordered
with black; IX-X devoid of dark color. Dorsal surface of VII
and VIII darker than other segments. Posterior segments
becoming narrower; IX narrow. Prolegs on III- VI and X.
One pair of somewhat conical, fleshy projections on lateral
aspects of each segment; one short, ventral seta and a longer,
dorsal seta, latter about 0.27 mm. long, on each projection.
Segment IX with four pairs of well-developed setae on dorsal
and lateral surfaces. Segment X with a pair of short setae and
one pair of longer setae on dorsal surface; three setae, two short
and one longer, on each lateral surface; two setae on caudal
margin; and two very long setae, 1.06 mm. in length, extending
from the latero-caudal angles of posterior margin.

Second Instar. — This instar, as such, has not been described.
Forbes ('10, p. 221), in his account of the life history of this
species, states that /* stage II'* was **not seen; and no sign of
leaf -mining was noticed." The same writer describes ** stage



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1916] Biology of Aquatic Lepidoptera 167

Iir*, using an interrogation mark to indicate uncertainty, as
follows: **A transparent caterpillar, essentially like the full-
grown ones. The maximum number of gill-filaments is two, and
the anterior suprastigmatals and the last three pedals have but
one. Length about 4 mm.; head .6 mm." The writer has
reared larvae through the early stages from eggs laid by females
in the aquaria and observed no indication of an instar between
the first and the one described below as the second, the latter
corresponding rather closely to the description of Forbes for
''Stage III. (?)".

A rather surprising change (Fig. 2) takes place at the first
ecdysis. The general shape of the larva is not changed but new
structures appear. Measurements show the body to be about
2.5 mm. long. It is almost transparent, and the color of the
material in the digestive tract shows through the body-wall,
giving combinations of yellow and green to the general color.

Head about 0.38 mm. wide, otherwise as in the first instar.
Thorax with margins of cervical shield black, remainder trans-
lucent ; prothorax with five pairs of well-developed setae ; meso-
thorax with one pair lateral, filamentous gills; length of each
gill about equal to width of corresponding segment ; metathorax
with two lateral, filamentous gills on each side, both of similar
length and resembling meso thoracic gills. Legs translucent.
Meso- and metathorax devoid of dark color. Abdomen without
dark markings ; two lateral gill filaments on each side of all seg-
ments except last two, one filament with length about equal to
width of corresponding segment, the other about one-fourth
shorter; penultimate segment with one lateral, filamentous gill
on each side, about as long as width of segment ; ultimate segment
devoid of gills. No gills on dorsal surface of body. Last two
segments with several pairs of setae, one pair of which is terminal
in position, long, and stout. Otherwise similar to first instar.

The interesting part of the change from the first to the second
instar is the initial appearance of the tracheal gills in the latter.
In most of the specimens studied, the lateral gills were constant
•in all respects, but a few showed variation from the typical
condition. One specimen showed a small, extra gill on the left
:side of the ventral surface of the second abdominal segment.
Another specimen bore only one gill on the right side of abdom-
inal segments II, III, IV, and the left side of abdominal
•segments II and VII.



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168 Annals Entomological Society of America [Vol. IX,

Third Instar, — The conditions under which these larvae must
be reared make it very difficult to follow the ecdyses so that the
exact number of instars can be determined. The following
described instar is identified in this paper as the third since, in
the examination of many specimens of different ages in the
field and laboratory, no indication of an instar between it and
the second could be found. Larval changes were also followed
as accurately as possible in specimens reared from eggs and
the same result was obtained. The writer believes that the
results warrant the designation of this form of the caterpillar
(Fig. 3) as the third instar.

Length, 4-5 mm. General color pale yellowish. Head
about 0.44 mm. wide, otherwise very similar to second instar.
Thorax with anterior margin of cervical shield dark, remainder
translucent; five pairs of setae on prothorax; mesothorax with
one pair of lateral, filamentous gills and one pair of dorsal,
filamentous gills; metathorax with three pairs of filamentous
gills, one pair laterad, one pair dorsad, and another pair ventrad.
First abdominal segment with three pairs of gills similar in
shape and position to those of metathorax; segments II and III,
with one pair of dorsal, two pairs of lateral, and one pair of
ventral gills; abdominal segments IV and V with two pairs of
lateral and one pair of dorsal gills; segments VI, VII, and VIII,
with two pairs of lateral gills; segment IX with one pair of
lateral gills; segment X devoid of gills; segments IX and X
with several pairs of setae, one of which is terminal in position
and much longer than others.

It will be noticed that the above description agrees to sonie
extent with that given by Forbes for ''Stage IV'\ the chief
difference being in the maximum number of gill filaments.
Although the writer has never found an instar in which the
maximum number of gill filaments was three, he is inclined to
believe that the third instar of this paper is the same as ''Stage
IV djescribed by Forbes.

Later Instars. — Examination of a large series of caterpillars,
varying from the third instar to the full-grown state, showed
the existence of a number of types, based on gill characteristics,
gradating from the former to the latter. Each successive type
is characterized by increase over the preceding one in body size
and in the number of gill filaments. Whether or not each type



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1916] Biology of Aquatic Lepidoptera 169

represents an instar has not been determined and the discussion
of later instars will be left for a future paper. The full-grown
larva has been studied by Forbes ('10, p. 221) and the specimens
studied in this connection agree with his description in most
regards, assuming that his table of gill nimibers represents an
average condition and not a constant one. The most striking
change in the later larval instars is the remarkable increase in
the number of gills. The maximtun number of gills per segment
increases from two in the second instar to as many as ten per
segment in the full-grown larva. The total number of gills
increases from twenty-two in the second instar to one himdred
in the last one. The number of gill filaments per segment
increases from four in the second instar to as many as forty-eight
in the mature larva. The total number of gill filaments on the
whole body increases from forty to over four hundred. Such
a provision of tracheal gills would seem- to be adequate for a
wide range of aquatic conditions.

Activities of the Larva.

Locomotion. — The young larvae are active from the moment
of hatching, crawling restlessly about ovfer the egg shells and
the adjacent leaf surface. Locomotion on the water-lily leaves
consists exclusively of crawling movements. In the younger
instars, particularly in the first, this method of locomotion is
slow, often appearing awkward and inefficient. Crawling, in
the older instars, is more active and vigorous and, under normal
conditions, constitutes a comparatively efficient form of loco-
motion. The efficiency of crawling as a method of locomotion
depends upon the character of the supporting surface. On
the yellow water-lily leaf, crawling is accomplished with some
degree of ease, except when the leaf, bearing larvae on the upper
surface, is submerged, a condition which seems to require extra
effort. Crawling on the glass surfaces of the aquaria is very
slow and inefficient, consisting of little more than a mere, clinging
to the glass, and change of position is accomplished with
difficulty. Other surfaces of a smooth, firm nature also afford
difficulties in crawling.

At no time during the larval period did the writer observe
any evidence of an ability to swim. In this connection, a num-
ber of experiments were tried with larvae of all ages but results
were always negative. Random, writhing movements were



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170 Annals Entomological Society of America [Vol. IX,

exhibited when larvae were submerged apart from a supporting
surface but such movements were ineffective so far as change of
position was concerned. However, another form of locomotion
will be described later in connection with the discussion of
case-making which serves as a substitute for true swimming.

Case-making. — A very interesting phenomenon in connection
with the life history of N. maculalis is the case-making activities
of the larva. This habit is common to the genus Nymphula,
both in foreign and native species. Of the latter, Packard ('84,
p. 824) gave a brief account of case-making by what was
apparently N. icciusalis Wlk. Hart ('95, pp. 167-172, 176-180)
described it in N. (Paraponyx) obscuralis Grt. and N. (Hydro-
campa) obliteralis Wlk. Forbes ('10, pp. 220-21) gave a brief
description of case-making in N. maculalis Clem.

The observations of the writer confirm, in most respects,
the brief description of Forbes on case-making in N. maculalis.
However, a number of additional data have been secured and
will be discussed in some detail. As mentioned above, the
larvae are active from the moment of hatching. They emerge
from the eggs and wander about restlessly for a time before
starting to feed. In some of the aquaria, this period of prelim-
inary wandering lasted for two or three hours. In the lab-
oratory, the young larvae seemed to show a preference for the
submerged lower side of the leaf on which they were reared.
The young larva, under laboratory conditions, soon began to
make an incision in the leaf which was extended in such a way
that ultimately a portion of the leaf, oval or circular in form
and about 2 mm. in maximum dimension, was cut out and
drawn back on the lower surface of the yellow water-lily leaf so
that the larva was enclosed. Sometimes the larva cuts out the
upper surface of its compartment, thus making an independent
case composed of two similar pieces of leaf tied together by
silken threads.

As the larva increases in size, the cases are outgrown and
new ones made. With the older larvae, case-making is a simple
and rather rapid process. In constructing a new case, the larva
crawls to the lower surface of a leaf and usually begins work
near the periphery so that the resulting piece is cut out of the
edge. However, an occasional leaf is found in which the piece
has been cut out near the midrib. Certain random, preliminary



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1916] Biology of A qtuitic Lepidoptera 171

movements are often performed, consisting chiefly of an
apparent testing of the lower epidermis with the mandibles,
before the larva settles down to the work of removing the piece.
It works by using most of the length of the body as a radius and
bending the anterior region as the incision is extended. After
the initial incision is made, the head is held into the cut and a
little to one side, thus placing the cutting plane of the mandibles
at approximately right angles to the surfaces of the leaf. One-
third of the complete incision may be made without changing
the position of the posterior part of the body. Occasionally, a
larva takes advantage of the overlapping margins of con-
tiguous leaves. Since such a space is usually filled with water,
the larva crawls into it, begins work, and in due time cuts an
elliptical piece from one or both of the leaves.

The older larvae utilize the excised pieces in making cases in
several ways:

(1) A single piece may be cut out and tied flatwise against the lower side of

the leaf.

(2) Two similar pieces may be cut out, forming a lens-shaped case, which

is then tied flatwise to the leaf, or else becomes independent.

(3) Several pieces may be cut out, tied together into a case, and attached to

the lower surface of the leaf.

(4) Two pieces may be cut out, tied together flatwise, and then attached

endwise to the leaf.

The majority of the cases are placed on the lower, submerged
surfaces of the floating leaves. Occasionally, cases containing
larvae are found on the dry, upper surfaces, a fact which suggests
"the possibility that the larvae are not entirely dependent upon
respiration by tracheal gills. It is a common thing to find
numerous cases of various sizes attached to both surfaces of the
submerged leaves of Nymphcea americana. How these larvae
get on the submerged leaves is not definitely known but it is
possible that some of them, by wave action or other mechanical
means, are dislodged from the floating leaves and sink to the
submerged leaves, or else to the bottom from whence they crawl
up the petioles to the leaves. The presence of young larvae in
such situations is discussed later.

The chief functions of the case appear to be (1) protection,
and (2) support in the water. The protective function plays
an important part in the life of the larva. These caterpillars
occur in an environment where predaceous enemies are common
and obviously the case is a rather efficient protection. The
larva shows a very distinct tendency to respond to slight



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172 Annals Entomological Society of America [Vol. IX,

mechanical stimuli by immediate retraction into the case, a
reaction which probably plays an important part in escaping
enemies. Under normal conditions, the larva is apparently
very shy, never, according to the observations of the writer,
emerging completely from the case except in connection with
the construction of a new one. At times, the anterior two-thirds
Qf the body is projected from the case but such periods of
partial emergence are of short duration, except when engaged in
a special form of locomotion to be described later. Larvae,
removed from their cases and placed in aquaria provided with
yellow water-lily leaves, very soon begin the construction of
a new case.

The second function of the case — that of support in the
water — is vitally connected with an interesting form of locomo-
tion. The specific gravity of the older larvae is greater than that
of water and, unless supported, they will sink. The leaf tissue of
the yellow water-lily has a specific gravity distinctly less than
that of water and the oblong pieces cut out by the larva in
case-making are always buoyant enough to easily support it.
Therefore, all detached cases float at the surface and no effort
on the part of the larva is required to support itself in the
medium. Where larvae are numerous, individuals are often
found crawling over the top of the water-lily leaf, carrying the
cases with them. To accomplish this form of locomotion, the
larva extends the anterior part of the body from the case, uses
the true legs as locomotor organs, and holds the case with the
prolegs. When detached cases are dropped in the water, the
larva performs certain movements which result in a change of
position in space. As mentioned before, no evidence of an ability
to swim was observed when larvae were isolated from their cases.
However, they do possess a form of locomotion in water in con-
junction with their cases. The anterior portion of the body is
projected from the case into the water and vigorous, horizontal,
side to side motions are executed which result in the propulsion
of both larva and case. It does not constitute a very efficient
form of locomotion but is effective enough to bring the larva in
contact with other water-lily leaves. If the horizontal move-
ments are equal on either side of the long axis of the body, the
result is a backward movement approximately in a straight
line. If, as is often the case, the strokes are stronger on one
side than the other, the result is an irregular rotation.



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1916] Biology of Aquatic Lepidoptera 173

The effect of case-making upon the food plant is frequently
serious. Some of the yellow water-lily beds {N. americana)
about Douglas Lake are heavily infested at times with the
larvae of N. maculalis and suffer greatly (Figs. 12-19). The
total effect of the larvae on the food plant includes the amount
of plant tissue consumed as food and the plant tissue utilized in
case construction. According to the observations of the writer,
the plant suffers much more from the case-making than from
the removal of tissue for food. Case construction results in a
reduction of the leaf surface which may be extensive enough to
leave only the midrib. The writer observed beds of N. amer-
icana, in August, which, as nearly as could be estimated, had
lost 40 per cent, of the total leaf surface by the case-making
activities of these larvae.

Food. — Very young larvae, reared in shallow aquaria, fed on
the lower side of the yellow water-lily leaf, feeding and case-
making being accomplished at the same time. The translucency
of the body made it possible to observe the first occurrence of
green plant tissue in the digestive tract. After the case was
rnade, the tiny larva fed to some extent upon the tissue of the



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