The red-legged locust does considerable damage to cultivated crops, but its injuries are insignificant compared with the tremendous losses occasioned by a near relative, the Rocky Mountain Locust (Melanoplus spretus). This locust has its breeding-grounds on the high plateaus of the Rocky Mountain region, but it sometimes migrates in countless numbers southeast over the plains and into the great grain-fields of the Mississippi valley. Such migrations occurred in 1866, 1867, 1874 (in this year eighteen hundred and forty two families in Kansas were reduced to destitution by the utter wiping out of their crops by the locusts) and 1876. With the settling-up of the regions in which the Rocky Mountain locust breeds, there seems to have come a change of conditions, so that no great migrations have occurred since 1876.

THE GREAT WATER-SCAVENGER BEETLE (Hydrophilus sp.)

Technical Note.—The great water-scavenger beetles are large, black, elliptical insects common in quiet pools where they may be found swimming through the water, or crawling among the plants growing on the bottom. They are an inch and a half long and are readily distinguishable from all other water insects except the predaceous diving beetles (Dyticus). The antennæ of Hydrophilus, however, are thickened (clavate) at the tip, while those of Dyticus are thread-like for their whole length. The beetles may be readily collected with a water-net, and kept alive in glass jars or aquaria in water containing decaying vegetation.

External structure (fig. [39]).—Is the body of the water-beetle composed of segments? Can you make out three body-regions, head, thorax and abdomen? As in the locust the metathorax is fused with the first abdominal segment and with the mesothorax, while the prothorax is freely movable, and is covered above by a strong shield. The chitin armor of the whole body is specially heavy and strong, affording a great protection to the insect.

Fig. 39.—Ventral aspect of male great water-scavenger beetle, Hydrophilus sp.

On the flattened head note the compound eyes and the peculiarly-shaped nine-segmented antennæ. Are there any ocelli? Dissect out the mouth-parts. The beetle's mouth is fitted for biting, the mouth-parts being in general character like those of the locust, with distinct flap-like labrum, dentate mandibles, jaw-like maxillæ with long, slender, four-segmented palpi and lip-like labium with three-segmented palpi. Make drawings of the antennæ and mouth-parts.

Note the character of the thoracic segments. Examine the wings and legs. The fore wings are modified into strong horny sheaths, or elytra, which completely cover and protect the folded hind wings. The hind wings are large and membranous. How are they folded? Note the adaptation of the middle and hind legs for swimming. Determine the various segments of the legs, i.e. coxa, trochanter, femur, tibia and tarsus. Note the long longitudinal median keel on the ventral aspect of the thorax.

The abdomen articulates with the metathorax by the full width of the broad first abdominal segment. It is composed of a series of segments without appendages, of about equal length but decreasing in width from in front backwards. Of how many segments does the abdomen seem to be composed when viewed from the ventral aspect? From the dorsal?