National Geographic : 1927 Jul
STRANGE HABITS OF FAMILIAR MOTHS AND BUTTERFLIES may be unwilling host to a dozen para sites, and finally dies about the time the unwelcome guests are ready to pupate. Some parasites lay single eggs, from which as many as 300 larvae hatch (see illustration, page 8o). They are all of one sex, being in reality a single individ ual subdivided by witchery more subtle than the art of the greatest magician of fairy story. Polyembryony (meaning many individuals from a single egg) is one of the most marvelous of all the recent discoveries in biology. The caterpillars thrash their heads and tails about when the parasites come around them, and some species, like some of the Sphinx moths, make clicking and squeaking noises. The gamut which a caterpillar has to run to realize its ambition to reach the winged stage is shown by the researches of Slingerland and Crosby, who found that in some localities 90 per cent of the Tussock Moth caterpillars and chrysalids fell victims to parasites. Twenty differ ent species of flies and hymenopters para sitized those studied. But often a parasite is "hoist with his own petard," for 14 parasites were found preying on the Tussock Moth's parasites. And then these, in their turn, had para sites attacking them, reminding one of Dean Swift's famous bit of doggerel: So naturalists observe a flea Hath smaller fleas, that on him prey; And these have smaller still to bite 'em, And so proceed ad infinitum. TIIE PSYCHE CATERPILLAR MAKES ITSELF A SUIT OF CLOTHES Most caterpillars undergo four molts in reaching full growth, though some have been known to pass eight molts. Some change their color pattern after each molt, and most of them, preparing to molt, spin a silk web in which to entangle the legs of the old skin, so that it will remain anchored while they are escaping. Some caterpillars roll up leaves and make themselves individual shelters. Some species occupy these shelters when not feeding, which therefore last during their full larval life; others feed upon the walls of their abode, building a new shelter when they "eat themselves out of house and home." But there are others which make them selves suits of clothes. Whoever has failed to read Fabre's story of the life habits of the Psyche Moth and its caterpillar's coat has missed one of the gems of entomological litera ture. Commonly known as the bagworm, the Psyche caterpillar, on emerging from the egg, starts in to build a suit of clothes. Standing on its front legs and holding its tail upright, the naked creature spins a ring of silk, adding bits of wood, leaves, etc., thereto. It continues to spin, adding to the lower edge of the ring until the latter forms a sort of cone. As the worm grows, it enlarges the bag much after the fashion that hornets en large their nests. When the coat gets too heavy, the worm lets it hang down, and henceforth the creature thus encumbered must crawl around on its front legs, en cased in a hard, stiff, rough armor. Finally the migratory instinct subsides and the bagworm settles down on the twig of a tree that will constitute the food of its successor. After fastening its wood-embroidered garment to the twig, the insect lines the former with heavy silk, rests awhile, casts its skin, and be comes a chrysalis. Three weeks later the male chrysalis works himself down to the bottom of his bag, bursts the pupal skin asunder, emerges a full-fledged moth, and as soon as the glue that reinforces his wings is hardened he goes in quest of his mate. And what a poor creature this mate is. Wingless and footless, she is doomed to die in the home she has built. She creeps down out of her chrysalis skin, welcomes her mate at the door of her house, backs into her chrysalis skin again, fills it par tially with eggs, seals it up with what little is left of her body, and dies. A CATERPILLAR THAT STARS IN THE ROLE OF WEATHER FORECASTER Most of us are familiar with the tent caterpillars of spring, summer, and fall. Closely related to our everyday apple tree tent caterpillar is the Pine Processionary of France, which Fabre proved to be at once the prize "bone head" and the blue ribbon weather forecaster of the insect world (see illustration, page 82).