Phasmatodea

The Phasmatodea (sometimes called Phasmida) are an order of insects, whose members are variously known as stick insects (in Europe and Australasia), walking sticks or stick-bugs (in the United States), phasmids, ghost insects and leaf insects (generally the family Phylliidae). The ordinal name is derived from the Ancient Greek phasma, meaning an apparition or phantom, and refers to the resemblance of many species to sticks or leaves. Their natural camouflage can make them extremely difficult to spot.

Contents 1 Anatomy and ecology 2 Taxonomy 3 Species 4 Behaviour 5 Stick insects as pets 6 Notable species 7 References 8 External links

Anatomy and ecology

Phasmids can be relatively large, elongated insects. Some have cylindrical stick-like bodies, while others have a flattened, leaflike, shape. The body is often further modified to resemble vegetation, with ridges resembling leaf veins, bark-like tubercles, and other forms of camouflage. A few species, such as Carausius morosus, are even able to change their pigmentation to match their surroundings. Many species are wingless, or have reduced wings.^[1]

The mouthparts project out from the head, and include typical chewing mandibles. All phasmids possess compound eyes, but ocelli are only found in some winged males.^[1]

The thorax is long in the winged species, where it includes the flight muscles, but is typically much shorter in the wingless forms. Where present, the first pair of wings are narrow and cornified, while the hind wings are broad, with straight longitudinal veins and multiple cross-veins. The legs are typically long and slender, and some species are capable of limb autotomy.^[1] A few species (for example those in the genus Anisomorpha) are capable of secreting a substance from glands on the metathorax that can cause an intense burning irritation of the eyes (and in some cases temporary blindness) and mouth of potential predators on contact.

Phasmids are herbivorous, feeding mostly on the leaves of trees and shrubs. The females, which are usually significantly larger than the males, lay their eggs individually, either sticking them to vegetation or simply depositing them on the ground. A single female may lay from 100 to 1,200 eggs after mating, depending on species. The eggs are typically camouflaged, resembling plant seeds, and may remain dormant for a full season or more before hatching. The nymphs are born already closely resembling the adults.^[1]

Taxonomy

The classification of the Phasmatodea is complex. There are many people, including amateur entomologists, studying the order, and revisions are commonplace.

The Phasmatodea were considered a suborder of Orthoptera, although most authors now consider them to form an order of their own. There is much confusion over the ordinal name, with Phasmida being preferred by many authors, although it is incorrectly formed. Phasmatodea is correctly formed, and is gaining in popularity. The term "Cheleutoptera" is now considered outdated.

They are sometimes considered related to other orders, including the Blattaria, Mantodea, Notoptera and Dermaptera, but the affiliations are uncertain and the grouping (sometimes referred to as "Orthopteroidea") may be paraphyletic and hence invalid in the traditional circumscription.

Species

There are in excess of 3,000^[2] described species, with many more yet to be described, both in museum collections, and in the wild. The order has a worldwide distribution, but most species are found in the tropics. These tropic species vary from stick like species to those resembling bark, leaves and even lichens.

Behaviour

Stick insects, like praying mantis, show rocking behaviour in which the insect makes rhythmic, repetitive side-to-side movements. Functions proposed for this behaviour include the enhancement of crypsis by means of the resemblance to vegetation moving in the wind. However the repetitive swaying movements may be most important in allowing the insects to discriminate objects from the background by their relative movement, a visual mechanism typical of simpler animals. Rocking movements by these generally sedentary insects may replace flying or running as a source of relative motion of objects in the visual field.^[3]

See also Phasmatodea life cycle

Stick insects as pets

Many stick insects are easy to care for, and make good pets. Almost 300 species have been reared in captivity.^[4]

The most commonly kept, the Indian (or Laboratory) stick insect, Carausius morosus, requires a tall (25+ cm) vivarium (even a jar with a few holes punched in the top), some bramble, ivy, privet and lettuce and an atmosphere at room temperature. Indian stick insects are almost all female with only a few half-males (gynandromorphs) and these are not needed for reproduction. They reproduce by parthenogenesis and seem content living on their own. All stick insects moult and may eat the shed skin. By the sixth moult the Indian stick insect will lay eggs.

Many of the other species of phasmids kept in captivity will feed on bramble. However, some are very specialist feeders and are therefore more difficult to rear. Beginners often make the mistake of thinking all species will feed on privet (the plant most commonly used to feed the Indian stick insect), in fact few species feed on privet. Most of the privet feeders on the Phasmid Study Group's culture list belong to the family Pseudophasmatidae and are from South America, several of these will also feed on hebe. The few members of the family Aschiphasmatidae that have been reared have to be fed on fuchsia, willow herb, or evening primrose. Some of the species in the subfamily Necrosciinae will only feed on hypericum. it also eats leaves

Notable species

One Australian species, the Lord Howe Island stick insect, is now listed as critically endangered. It was believed extinct until its rediscovery on the rock known as Ball's Pyramid. There is a large effort in Australia to rear this species in captivity.

Females of the genus Phobaeticus are the world's longest insects, measuring up to 33 centimetres (13 in) from head to tip of abdomen.^[5]

Adult female Heteropteryx dilatata are likely to weigh up to 65 grams (2.3 oz), and captive bred specimens have been known to weigh in the order of 50 grams (1.8 oz).

The best known of the stick insects is the Indian or Laboratory stick insect (Carausius morosus). These insects grow to roughly 10 centimetres (3.9 in). They reproduce parthenogenically and males are unrecorded, although part male part female gynandromorphs are relatively common.

References

• Cameron, Stephen L.; Barker, Stephen C. & Whiting, Michael F. (2006): Mitochondrial genomics and the new insect order Mantophasmatodea. Molecular Phylogenetics and Evolution 38: 274–279. doi:10.1016/j.ympev.2005.09.020 (HTML abstract)

External links

• The Phasmid Study Group
• Phasmatodea.org
• Phasmatodea.com
• Phasmida Species File
• New Zealand Stick Insect Web Site