The group's name is derived from the Ancient Greek φάσμα phasma, meaning an apparition or phantom, referring to their resemblance to vegetation while in fact being animals.

Their natural camouflage makes them difficult for predators to detect; still, many species have one of several secondary lines of defense in the form of startle displays, spines or toxic secretions.

In hotter climates, they may breed all year round; in more temperate regions, the females lay eggs in the autumn before dying, and the new generation hatches in the spring.

[9] Phasmids have an impressive visual system that allows them to perceive significant detail even in dim conditions, which suits their typically nocturnal lifestyle.

Lessened sensitivity to light in the newly emerged insects helps them to escape from the leaf litter wherein they are hatched and move upward into the more brightly illuminated foliage.

The heel pads are covered in microscopic hairs which create strong friction at low pressure, enabling them to grip without having to be peeled energetically from the surface at each step.

Most phasmids are known for effectively replicating the forms of sticks and leaves, and the bodies of some species (such as Pseudodiacantha macklotti and Bactrododema centaurum) are covered in mossy or lichenous outgrowths that supplement their disguise.

[17] In a seemingly different method of defense, many species of Phasmatodea seek to startle the encroaching predator by flashing bright colors that are normally hidden, and making a loud noise.

[18] When disturbed on a branch or foliage, some species, while dropping to the undergrowth to escape, will open their wings momentarily during free fall to display bright colors that disappear when the insect lands.

[18] Some species, such as the young nymphs of Extatosoma tiaratum, have been observed to curl the abdomen upwards over the body and head to resemble ants or scorpions in an act of mimicry, another defense mechanism by which the insects avoid becoming prey.

[15] Some species are equipped with a pair of glands at the anterior (front) edge of the prothorax that enables the insect to release defensive secretions, including chemical compounds of varying effect: some produce distinct odors, and others can cause a stinging, burning sensation in the eyes and mouth of a predator.

[21] Additionally, the chemistry of the defense spray from at least one species, Anisomorpha buprestoides, has been shown to vary[21] based on the insect's life stage or the particular population it is part of.

[24] Some species employ a shorter-range defensive secretion, where individuals bleed reflexively through the joints of their legs and the seams of the exoskeleton when bothered, allowing the blood (hemolymph), which contains distasteful compounds, to discourage predators.

There, the egg hatches and the young nymph, which initially resembles an ant (another instance of mimicry among Phasmatodea), eventually emerges from the nest and climbs the nearest tree to safety in the foliage.

Didymuria violescens, Podacanthus wilkinsoni and Ctenomorphodes tessulatus in Australia, Diapheromera femorata in North America and Graeffea crouani in coconut plantations in the South Pacific all occur in outbreaks of economic importance.

[32] Indeed, in the American South, as well as in Michigan and Wisconsin, the walking stick is a significant problem in parks and recreation sites, where it consumes the foliage of oaks and other hardwoods.

Control efforts in the case of infestations have typically involved chemical pesticides; ground fires are effective at killing eggs but have obvious disadvantages.

[33] In New South Wales, research has investigated the feasibility of controlling stick insects using natural enemies such as parasitic wasps (Myrmecomimesis spp.).

[36] However, Brock and Marshall argue:[37] Phasmida is the oldest and simplest name, first used by Leach in 1815 in "Brewster’s Edinburgh Encyclopaedia" volume 9, p. 119, and widely used in major entomological textbooks, dictionaries and many scientific papers and books on phasmids.

As there is no compulsion to select the "grammatically correct" name [which some argue is Phasmatodea Jacobson & Bianchi, 1902], selection of a long established (and simple) name is reasonable, although the probability of persuading all colleagues to agree on the use of Phasmida is unlikely.The order Phasmatodea is sometimes considered to be related to other orders, including the Blattodea, Mantodea, Grylloblattodea, Mantophasmatodea and Dermaptera, but the affiliations are uncertain and the grouping (sometimes referred to as "Orthopteroidea") may be paraphyletic (not have a common ancestor) and hence invalid in the traditional circumscription (set of attributes that all members have).

[39] The traditional division is into the suborder groups Anareolatae and Areolatae, which are distinguished according to whether the insect has sunken areola, or circular areas, on the underside of the apices of the middle and hind tibiae (Areolate) or not (Anareolate).

[41][42][43] Recent taxonomic treatments recognise two suborders,[43] with Agathemeridae placed in Pseudophasmatoidea within Euphasmatodea[44] and Agathemerodea treated as nomen dubium[45] While suggestions have been made that various insects extending back to the Permian epoch represent stem-group phasmatodeans, the earliest unambiguous members of the group are the Susumanioidea, which first appeared during the Middle Jurassic, and usually have two large pairs of wings.

In size and cryptic (leaflike) body form, it closely resembles extant species, suggesting that the behavior of the group has changed little since that time.

[54] Fossils of the extinct genus and species Eoprephasma hichensi have been recovered from Ypresian age sediments in the U.S. state of Washington and British Columbia, Canada.

Their life cycle is annual, living only during the hottest months (especially genera Leptynia and Pijnackeria), which usually means late spring to early autumn.

Rocking movements by these generally sedentary insects may replace flying or running as a source of relative motion to help them discern objects in the foreground.

Occasionally, the consort will strike out at the competitor with the mid femora, which are equipped with an enlarged and hooked spine in both sexes that can draw the blood of the opponent when they are flexed against the body to puncture the integument.

If he is discovered, the males will enter into combat wherein they lean backward, both clasped to the female's abdomen, and freely suspended, engage in rapid, sweeping blows with their forelegs in a manner similar to boxing.

[60] Droppings of the stick insect Eurycnema versirubra (Serville, 1838) [=Eurycnema versifasciata] fed with specific plants are made into a medicinal tea by Malaysian Chinese to treat ailments.

[66] The video game Disco Elysium includes a storyline centered around a giant stick insect and cryptid called the insulindian phasmid.