Phylliidae

The Phylliidae family—sometimes misspelled as Phyllidae—belongs to the stick insect group and includes all living species known as true leaf insects or walking leaves. These creatures are among the most convincing leaf mimics in nature. Since Phylliidae is the sole family within the subfamily Phylliinae, and that subfamily is the only one in the superfamily Phyllioidea, the terms "leaf insect" and these taxonomic ranks are essentially interchangeable. Their range stretches from South Asia, through Southeast Asia, and into Australia.

Body length varies widely: the smallest males, like those of *Microphyllium spinithorax*, reach just 24 millimeters, while females of *Pulchriphyllium giganteum* and certain *Cryptophyllium* species can measure 105 to 120 millimeters. The body is flattened horizontally and widened to look like a leaf, with legs also bearing leaf-like lobes that enhance the disguise. Colors depend on species and location, ranging through greens, yellows, browns, and reds; some individuals are speckled, others nearly solid. Certain species show considerable color variation. In the past, some species—such as *Pulchriphyllium crurifolium*—were described multiple times, creating many synonyms. Earlier assumptions held that individual species had highly variable body shapes and huge geographic ranges, but recent research shows that most of those synonymized species are actually distinct, valid species with much smaller distributions.

Females are always larger and broader than males, looking more leaf-like thanks to a very wide abdomen and short mesonotum. Their forewings (tegmina) usually develop into leaf-shaped covers that often hide the entire abdomen. Hindwings (alae) are missing or just tiny in most females, though they are well developed in most *Cryptophyllium* females, as well as in *Phyllium ericoriai* and *Phyllium bonifacioi*. Males are smaller and narrower, with short forewings and fully developed, usually transparent hindwings that let them fly short distances. They also typically have three simple eyes (ocelli) on the top of the head between the compound eyes. Male antennae are much longer than those of females, have bristles, and consist of 20 to 26 segments; female antennae always have nine segments and are only as long as the head. These antennae are often modified into stridulatory organs. The abdomen has ten segments: the first is fused with the metanotum, while the other nine are free. A transverse groove on the underside marks where the metanotum meets the first abdominal segment. The subgenital plate sits at the end of the eighth abdominal segment, covering the genital opening and the ovipore. On the tenth abdominal sternum of males lies the vomer, a movable sclerite that anchors the male to the female's seventh abdominal sternum during mating. This vomer is usually species-specific in shape and has a single hook in nearly all species; only male *Cryptophyllium* have vomers with two hooks.

Living leaf insects are found from the Seychelles, across Sri Lanka and India, through the Asian mainland (including Nepal, Bangladesh, and southern Chinese provinces), Southeast Asia, northern Queensland in Australia, and east to Melanesia. *Pulchriphyllium* has the westernmost range, from the Seychelles through Sri Lanka, India, the Southeast Asian Peninsula, Sumatra, and Borneo. *Cryptophyllium* lies somewhat northeast, starting in Sri Lanka and extending north through Nepal, the Indian states of West Bengal and Assam, and the Chinese regions of Tibet, Yunnan, Guangxi, and Hainan; southeastward it reaches Sulawesi, the Philippines, and the Micronesian island of Yap. *Phyllium* species occur further east and south, covering the entire Philippines and Indonesia, plus the Malaysian part of Borneo, the Malay Peninsula, and New Britain. *Microphyllium* and *Pseudomicrophyllium* live only in the Philippines. *Nanophyllium* is found east of the Weber Line, on New Guinea and nearby islands, as well as in northeastern Australia, where *Walaphyllium* also occurs. *Acentetaphyllium*, *Rakaphyllium*, *Comptaphyllium*, and *Vaabonbonphyllium* are also on New Guinea, with the last also reaching the Solomon Islands. *Trolicaphyllium* species are native to New Caledonia, further southeast. *Chitoniscus* has the easternmost distribution, extending to the Fiji Islands.

Leaf insects are herbivores, feeding on leaves of tropical plants—some of which remain unidentified—as well as those of *Psidium*, *Theobroma cacao*, Myrtaceae, *Mangifera indica*, and *Camellia sinensis*.

Their camouflage is so accurate that predators often cannot tell them from real leaves. Some species even have body edges that look like bite marks. To add to the illusion, they rock back and forth while walking, mimicking a leaf blown by the wind. In females, the large, leaf-shaped forewings, when resting on the abdomen, strongly suggest the midrib and veins of an ordinary leaf. The scholar Antonio Pigafetta was probably the first Western person to describe them.