Effect of spraying behavior and body size on predators of the big head stick insect Megacrania tsudai (Phasmatodea: Phasmatidae)

Abstract

Some insects use multiple defensive methods, although little research exists on the complementary effects of these strategies on their predators. For example, Megacrania tsudai uses crypsis to blend with its background and when threatened it uses a chemical spray. However, the effectiveness of the spraying defense is unclear, although some potential predators were known. This study aimed to reveal the effect of the secondary defenses of M. tsudai. Although the liquid chemical amount changes with growth stages, neither geckos, frogs, spiders nor insects could predate M. tsudai when it grew to a certain size, regardless of the spray effectiveness. Therefore, at the fifth instar or older growth stages of M. tsudai, its predators were limited to birds. Megacrania tsudai that did not spray their liquid chemicals were attacked by predators (other than birds) more than species that sprayed the chemicals. Birds predated all instars regardless of the amount of liquid spray. In conclusion, M. tsudai mainly uses cryptic coloration for predators using visual sense such as diurnal birds, and body size and chemical defenses for other predators, as its defensive measure. The defensive strategy of M. tsudai could relate to its life history.