COLEOPTERA. 
503 
The aquatic, carnivorous, pentamerous Coleoptera, form a third tribe, that of 
The Hydrocanthari, or Swimmers. 
Their feet are formed for swimming, the four posterior being compressed and ciliated, or in the form 
of plates, and the two hind ones are far apart from the others. The mandibles ai-e nearly covered [by 
the upper lip] , the body is always oval, with the eyes slightly prominent, and the thorax much broader 
than long : the hook which terminates the maxillae is curved from the base ; the ungues are often unequal. 
These insects compose the genera Dytiscus and Gyrinus of Geoffrey. They pass the first and the 
last state of their existence in fresh water, such as lakes, pools, and ditches. They swim well, and 
rise to the surface of the water from time to time to respire, ascending easily by holding their feet 
still and suffering themselves to float. The body being turned upside down, they slightly elevate the 
tip of the body above the surface of the water, raising the extremity of the elytra or bending down the 
abdomen, so that the air introduces itself into the spiracles, which they cover, and from thence into 
the tracheae. They are very voracious, and feed upon small animals which, like themselves, ordinarily 
reside in the water, which the Hydrocanthari only leave at the approach of or during the night. When 
taken out of the water they emit a very disagreeable odour. They are sometimes attracted by the 
light into the interior of houses. Their larvae have the body long and narrow, composed of twelve 
segments, of which the first is largest, with the head strong, and armed with two powerful mandibles, 
which are curved into an arch and pierced near the tips ; they have also short antennae, palpi, and six 
simple eyelets close together on each side of the head. They have six feet of moderate length, often 
fringed with hairs, and terminated by two small hooks. They are active, carnivorous, and respire 
either by the anus, or by a kind of swimmerets resembling gills. Tliey quit the water in order to 
undergo their metamorphosis into pupae. 
This tribe is composed of two principal genera. 
Dytiscus, Geoff.,* — 
Which have thread-like antennae longer than the head, two eyes, the fore legs shorter than the fol- 
lowing, and the posterior often terminated by a compressed tarsus finishing in a point. They swim 
wdth great quickness by the assistance of their feet, fringed with long hairs, especially the posterior 
pair. They dart forward upon other insects, aquatic worms, &c. In the majority of the males the 
four anterior tarsi have the three basal joints dilated and spongy beneath ; those of the first pair are espe- 
cially remarkable in the large species, in which these three joints forma broad plate, the under surface of 
which is covered with small bodies, some of them like warts and others like small suckers. Some females 
are distinguished by their elytra being furrowed. The larvse have the body composed of eleven or twelve 
segments covered by scaly plates ; they are long, swollen in the middle, and slenderer at each end, especially 
when the terminal segments form an elongated cone fringed at the sides with floating hairs, with which 
the animal beats the water and thus propels the body forwards, which is ordinarily terminated by two 
conical bearded and moveable filaments, between which are two small cylindrical bodies pierced with 
a gutter, at the extremity which are aerial channels, to which are attached twm tracheae ; moreover, the 
sides of the body are provided with spiracles : the head is large, oval, attached to the thorax by a neck 
with strongly-armed mandibles, beneath the extremity of which De Geer observed a longitudinal slit, so 
that these organs resemble the mandibles of the larvae of the Myrmeleons, or Ant-lions, and serve them 
for suckers : the mouth offers besides a pair of maxillae and a lip with palpi : each of the three first 
segments supports a pair of moderately long legs, of wEich the tibia and tarsus are fringed with hairs, 
which are serviceable in swimming ; the first segment is the broadest or longest, and defended beneath, 
as well as above, by a scaly plate. 
These larvae suspend themselves at the surface of the water by means of two appendages at the sides 
of the tail, which they keep dry by raising them above the surface. Wlien they wish to change their 
place suddenly, they give their body a quick and vermicular movement, beating the water with the 
tail. They especially feed upon the larvae of Dragon-flies, Gnats, Tipulae, Aselli, &c. When the period 
of their transformation has arrived, they quit the water and bury themselves under the earth of the ad- 
jacent hanks, keeping, however, in very damp situations, where they form an oval cavity in which they 
♦ [Latreille is incorrect in giving Geoffrey as the author of the I contrary, • corrected it to Uyticus, being derived from the Greek 
name Dytiscus, it having been proposed by Linnaeus. Gcoffroy, on the | Deutikos, urinatorius.] 
