Beetles 
2 57 
another near the base. When a live insect or other aquatic creature is caught 
by the active larva its body is pierced by the mandibles and the blood sucked 
through them into the mouth, the opening at the base just fitting, when the 
mandibles are closed, into the corners of the small silt-like mouth. Both 
larvae and adults are fierce and voracious, and the larger species attack and 
kill small fish. In the middle states these beetles actually do much damage 
in cjarp-ponds. The larva breathes through a pair of spiracles at the slender 
tip of its body, which is thrust up to the air when it comes to the surface 
of the water. When ready to pupate it leaves the water—breathing now 
also through six pairs of lateral spiracles—and makes a rough cell in the 
ground of the pond or stream bank. “The pupa state lasts about three 
weeks in summer; but the larvae that transform in autumn remain in the 
pupa state all winter.” 
The larger of our common species belong to Cybister, Dyticus, and 
allied genera. In Cybister the little cups on the under side of the tarsal 
disks of the male are similar, and arranged in four rows. In Dyticus and 
its allies the cups of the tarsal disks vary in 
size. Fig. 349 represents a common species of 
Dyticus. 
“ The most common of the diving-beetles 
that are of medium size belong to the genus 
Acilius. In this genus the elytra are densely 
punctured with very fine punctures, and the 
females usually have four furrows in each wing- 
cover.” 
An interesting account of the habits 
and special structures of the common large 
European diving-beetle, Dyticus marginalis, 
is given in Miall’s Natural History of Aquatic 
Insects, pp. 39-61. 
Smaller than the predaceous diving-beetles, Fig. 35 °- Fig. 351. 
and readily recognized by their curious spin- Fig. _ 350.— Whirligig - beetle, 
ning or circling, in companies, on the surface ^atoaT^sized^^^* ^ Twice 
of ponds or still pools in streams, are the Fig. 351.—Larva of whirligig- 
whirligig-beetles (Gyrinidae), common all over ^fter Sc B|” enlarged”' 
the country. About forty species of these 
beetles, varying in size from one-sixth to three-fourths inch in length, have 
been found in North America, three-fourths of them belonging to the genus 
Gyrinus. They are all of similar shape and steely blue-black in color, 
and have the compound eye, on each side, wholly divided into an upper 
and a lower part by the sharp lateral margin of the head. Like the 
Dyticids, the whirligig-beetles breathe at the surface and carry air down with 
