Phylliidae

The family Phylliidae (often misspelled Phyllidae) is a family of stick insects and contains the extant true leaf insects or walking leaves, which include some of the most remarkably camouflaged leaf mimics (mimesis) in the entire animal kingdom. Because the family Phylliidae is the only one within the subfamily Phylliinae - which in turn is the only subfamily within the superfamily Phyllioidea - leaf insects are often equated with these taxa. They occur from South Asia through Southeast Asia to Australia.

Characteristics Leaf insects can reach body lengths ranging from 24 millimetres (0.94 in) (male of Microphyllium spinithorax) to 105 to 120 millimetres (4.1 to 4.7 in) (females of Pulchriphyllium giganteum and certain Cryptophyllium species). They are characterized by a body that is horizontally flattened and broadened to resemble a leaf (mimesis). Their legs are also optimally adapted to this leaf mimicry through leaf-like expansions (lobes). Depending on the species and origin, leaf insects appear in various shades of green, yellow, brown, or reddish; some are speckled, while others are nearly uniform in color. Certain species exhibit significant color variation. In some cases, species such as Pulchriphyllium crurifolium were described multiple times, resulting in a number of synonyms. Previously, it was assumed that individual species possessed highly variable body shapes and occupied vast geographical ranges. Recent studies indicate, however, that species formerly synonymized on this basis are almost all distinct, valid species with significantly smaller distribution ranges. Females are consistently larger and significantly broader than males, bearing a stronger resemblance to leaves. This is due to their very broad abdomen and short mesonotum. Furthermore, the forewings (tegmina) of adult females are typically developed as leaf-like covers that often conceal the entire abdomen. Hindwings (alae) are either absent or merely vestigial in most females; they are well-developed only in the majority of females of the genus Cryptophyllium, as well as in Phyllium ericoriai and Phyllium bonifacioi. The smaller, narrower males usually possess short forewings and fully developed — mostly typically transparent — hindwings that enable short flights. They also generally feature three simple eyes (ocelli) on the vertex between the compound eyes. Their antennae are distinctly longer than those of the females and bear bristles; they consist of 20 to 26 segments, whereas the females' antennae are always composed of nine segments and extend only as far as the length of the head. These antennae are often modified into stridulatory organs. The abdomen is formed from ten segments; the posterior nine are free, while the first is fused with the metanotum. A transverse groove on the underside marks the transition between the metanotum and the first abdominal segment. The subgenital plate is located at the end of the eighth abdominal segment, concealing the genital opening and the ovipore. Located on the tenth abdominal sternum of the males is the vomer, a movable sclerite that serves to anchor the male to the female's seventh abdominal sternum during mating. It is usually shaped in a species-specific manner and bears a hook in almost all species; only the males of Cryptophyllium species have vomers with two hooks.

Occurrence

The distribution range of extant leaf insects extends from the Seychelles across Sri Lanka, India, and the Asian mainland - including Nepal, Bangladesh, and southern Chinese provinces - through Southeast Asia and northern Queensland (Australia) to eastern Melanesia. The genus Pulchriphyllium has the westernmost distribution, ranging from the Seychelles across Sri Lanka, India, the Southeast Asian Peninsula, and Sumatra to Borneo. The distribution of the genus Cryptophyllium lies somewhat further to the northeast; it begins in the west in Sri Lanka and extends further north, spanning Nepal, the Indian states of West Bengal and Assam, and the Chinese regions of Tibet, Yunnan, Guangxi, and Hainan. In the southeast, it encompasses Sulawesi and the Philippines, extending as far as the Micronesian island of Yap. Species of the genus Phyllium occur even further east and south; in addition to the entirety of the Philippines and Indonesia, they inhabit the Malaysian part of Borneo, the Malay Peninsula, and the island of New Britain. Microphyllium and Pseudomicrophyllium are found in the Philippines. The distribution of the genus Nanophyllium lies east of the Weber Line and includes New Guinea and surrounding islands, as well as northeastern Australia, where Walaphyllium also occurs. The genera Acentetaphyllium, Rakaphyllium, Comptaphyllium, and Vaabonbonphyllium are also found on New Guinea, with the latter also occurring in the Solomon Islands. The distribution of Trolicaphyllium species - native to New Caledonia - lies even further to the southeast. The genus Chitoniscus has the easternmost distribution, extending to the Fiji Islands.

Way of life

Diet and food plants Leaf insects are herbivorous insects that feed on the leaves of tropical plants - some of which are still unknown - as well as those of Psidium, Theobroma cacao, Myrtaceae, Mangifera indica, and Camellia sinensis.

Camouflage and defensive behavior

Leaf insects are well camouflaged, taking on the appearance of leaves. They do this so accurately that predators often are not able to distinguish them from real leaves. In some species, the edge of the leaf insect's body has the appearance of bite marks. To further confuse predators, when the leaf insect walks, it rocks back and forth, mimicking a real leaf being blown by the wind. In the female, this deceptive resemblance is enhanced by the large size and foliaceous form of the front wings, which, when at rest on the abdomen, forcibly suggest in their neuration the midrib and costae of an ordinary leaf. The scholar Antonio Pigafetta was probably the first Western person to document the species, though it was known to people in the tropics for a long time. Sailing with Ferdinand Magellan's circumnavigational expedition, he studied and chronicled the fauna on the island of Cimbonbon as the fleet hauled ashore for repairs. During this time he documented the Phyllium species with the following passage:

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