326 
BULLETIN OF THE BUREAU OF FISHERIES. 
meet on the mid line of the body; each has separate pockets for the spines at the distal ends of the 
tibiae. The large metasternal spine does not quite reach the tips of the second legs. 
Inside the pupal chamber the pupa rests upon the large spines of the prothorax and the posterior 
cerci, the dorsal surface uppermost and strongly arched. Of 10 pupae reared in 1919, 4 remained three 
days in the pupa stage, 4 remained four days, and 2 remained five days. Of 10 pupae reared in 1920, 
6 remained only three days in the pupa stage, while the other 4 remained four days. The pupae reared 
in 1920 emerged two weeks earlier in July than those in 1919, which may have had some influence on 
the length of the pupal period. 
Habits of the adult .— When first emerging from the pupa stage, this beetle is yellowish in color with 
black eyes, but with no other pigment visible. After emerging it remains about three days in the 
pupal chamber before coming out into the light, gradually turning a reddish-yellow, and finally black 
with yellow margins on the thorax and elytra. If taken from the chamber during this time and thrown 
into the water, it floats lightly on the surface like a whirligig beetle and swims for the shore or the 
nearest vegetation. Evidently it, can not submerge itself and manage its air supply at that stage. 
When fully matured, it is an excellent swimmer and is also agile upon land, walking and running 
easily but not jumping. It feeds largely upon Anabsena and Clathroeystis, which float upon the 
surface of most of the ponds during the summer. Turning bottom upward and clinging to the surface 
film with its legs, the beetle scoops in the floating algae with its labial and maxillary palps. Sometimes 
it clings to floating objects and reaches the algae from that foothold. 
Description of the adult . — General form elongate-ovate, with evenly rounded outlines, the abdomen 
often projecting a little from beneath the elytra. Total length 8 to 10 mm.; greatest width (through 
the thorax) 3 to 3.50 mm. Dorsal surface olive-black, shining; the head, thorax, and elytra with a 
narrow margin of pale yellow, and sparsely covered with fine silky hairs, longer on the margins, 
especially toward the posterior end of the elytra. Ventral surface black, the antennae, maxillae, legs, 
and wide margins on the thorax and elytra yellow. Bases of the femora and outer margins of the tarsi 
black, eyes pale lavender. 
The antennae are nine-jointed, the last four joints enlarged into a densely pilose club. Mandibles 
with a long and acute terminal tooth and a squarely truncated secondary tooth, the truncated edge 
cut into smaller teeth. From the posterior margin of the second tooth two divergent series of small 
comb teeth extend toward the base of the mandible. The maxillae are typical in form, the palps 
elongate, four-jointed, the last joint nearly one-third longer than the preceding one. The labial palps 
are three- jointed, short, and pilose. 
This beetle is easily recognized by the yellow borders of the thorax and elytra, which stand out 
sharply in contrast with the shiny black of the dorsal surface. It is decidedly the most abundant 
species around the fishponds; it is present and breeding in every one of them except the small 6D, 
and it is probably found there at times. Although the larvse are such ferocious little cannibals, they 
are not large enough to menace young fish, but, on the other hand, their- exceptional abundance makes 
them an important factor in fish food. 
Tropisternus glaber (Herbst). Figures 137, 140, 142, 143, 145. 
Hydrophilus glaber (Herbst, 1797, p. 398). 
Tropisternus glaber (Wickham, 1893a, p. 310). 
Tropisternus glaber (Richmond, 1920, p. 35, pi. 7, figs. 1-9). 
Eggs and egg case . — This beetle also spins a silken egg case similar to that of the preceding species 
but a little larger, and nearly always with a spike instead of a ribbon for a fag. 8 These cases are 6 to 
9 mm. long, 8 to 12 mm. wide, and 4 to 5 mm. high at the mouth. The number of eggs in a case varies 
greatly but averages about 10 or 12. Three or four days intervene between the laying and the hatching 
of the eggs. About 100 egg cases of this species were found in 1921 in pond 9D, in little patches of 
CEdogonium floating at the surface of the water. Under these conditions they were somewhat different 
from those described by Richmond (1920) and may be characterized as follows: Nearly spherical, about 
the same length and width, not flattened at all but fastened at various places to the algal strands, so 
that the case lies horizontally in the water. The cap is circular in outline, stands vertically upright, 
and is prolonged into a cylindrical fag 8 which tapers to a sharp point and which is always darker in 
color and coarser in texture than the white case and cap. 
s See p. 332. 
