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. [Illustration: 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.