At certain times of the year, freshets overflow the country inhabited by the “drivers,” and it is then that these ants go to sea. The rain comes suddenly, and the walls of their houses are broken in by the flood, but instead of coming to the surface in scattered hundreds and being swept off to destruction, out of the ruins rises a black ball that rides safely on the water and drifts away. At the first warning of danger, the little creatures rush together, and form a solid ball of ants, the weaker in the center; often this ball is larger than a common base-ball, and in this way they float about until they lodge against some tree, upon the branches of which they are soon safe and sound. And from this resting-place they escape by their curious bridges, a description of which was given in “Jack-in-the-Pulpit,” in ST. NICHOLAS for July, 1881. [Illustration: THE GREBE AND HER FLOATING NEST.] One would scarcely look for ship-builders among birds, so many of which are boats in themselves, going either upon or under the water; but in the curious family of grebes, one branch of which produces the beautiful feathers so coveted by ladies, there is one kind that forms a nest which is a veritable ark. Instinctively these birds seek the low boggy marshes to build their nests. But there they are in continual danger from the high tides that often cover the marshes, or from the drift-wood which washes in, or from many other accidents. So the ingenious grebe, looking like a clerk with feathery pens behind her ear, constructs a nest that will rise and fall with the tides, and can be moved from place to place. The boat is first built of rushes and grass; this is then packed with moss, and lined and relined until it is perfectly water-tight; and in this the eggs are laid. The home either is anchored to tufts of grass, or drifts, perhaps, here and there, though always guided by the mother-skipper, as she stands by the helm in all kinds of weather. We have seen that the spider is completely at the mercy of the wind, but the grebe propels her boat along. If the young are half grown, they readily take to the water; but if they are just hatched, the mother, at the approach of danger, steps upon one side of the boat, and uses one of her webbed feet as an oar to paddle away from the enemy into one of the innumerable inlets or lanes in the marsh, where she is almost sure to escape. [Illustration: THE SAILOR-FISH OF THE INDIAN OCEAN.]