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In Lepidoptera, forewings and hindwings are mechanically coupled and flap in synchrony. Flight is anteromotoric, being driven primarily by action of the forewings. Here we report that lepidopterans can still fly when their hindwings are cut off, a procedure reducing their total wing surface, on average, by nearly one half. However, as we demonstrate by analysis of three-dimensional flight trajectories of a moth and a butterfly (Lymantria dispar and Pieris rapae), hindwing removal causes lepidopterans to incur a loss in both linear and turning acceleration, so that they are unable to exercise their normal flight maneuverability. Without hindwings they still are able to zigzag aerially (the ablation has no effect on their turning radius in flight) but at lesser speed and therefore less evasively. Consequently, hindwings in the expanded state in which they occur in lepidopterans seem to contribute in an essential way to lepidopteran survival. Moths in today's world, we argue, may rely on their evasive flight primarily to avoid capture by bats, whereas butterflies, which we propose advertise their evasiveness collectively through shared aposematism, may depend upon it primarily for defense against birds. Aerial agility thus may be the chief adaptive asset derived by lepidopterans from possession of oversize hindwings.

The thyridid caterpillar, Calindoea trifascialis, when disturbed, emits a defensive secretion from two sac-like glands that open dorsolaterally on the first abdominal segment. The larva has two arm-like protuberances that project outward from the body just in front of the gland openings. These "arms", which are wetted by secretion when the larva activates its glands, appear to function specifically for administration of the fluid. A primary component of the secretion in mandelonitrile, a cyanogenic compound, but the fluid also contains other potential deterrents, including benzaldehyde, benzoic acid, (E,E)-alpha-farnesene, and 3-methylbutyl-3-methylbutanoate. Tests done in the field in Vietnam, where the species is native, showed the secretion to be protective against ants.

Pyrrolizidine alkaloid sequestered by adult male Danaus gilippus from plants is transferred in large measure to the female at mating, and by the female to the eggs. The eggs, presumably, are protected as a result. The male's courtship pheromone, danaidone, derived from the sequestered alkaloid, may function to advertise the male's alkaloid-donating capacity.

The eggs of Utetheisa ornatrix contain pyrrolizidine alkaloids. These compounds are contributed by both parents, who sequester them as larvae from their food plants. Females receive alkaloid from the males at mating, apparently by seminal infusion, and transmit this alkaloid together with alkaloid of their own to the eggs. Field and laboratory tests showed that the alkaloids protect eggs from predators. The alkaloidal contribution of the male, although smaller than that of the female, itself provides significant egg protection. A previously identified pheromone, derived by the male from the alkaloid and emitted during precopulatory behavior, may announce the male alkaloidal worth to the female.

Moths, by virtue of the loose scales that cover their wings and bodies, are admirably adapted to elude capture by orb-weaving spiders. Rather than sticking to the web, they may simply lose some of their scales to the viscid threads, and then fly on. Other insects, covered with detachable hairs or waxy powder, are similarly protected against entrapment. Quantitative data are presented on the adhesiveness of spider thread to insect cuticles oq various kinds.