Defense mechanisms

Phasmatodea species exhibit mechanisms for defense from predators that both prevent an attack from happening in the first place (primary defense) and are deployed after an attack has been initiated (secondary defense).
The defense mechanism most readily identifiable with Phasmatodea is camouflage. Most phasmids are known for effectively replicating the forms of sticks and leaves, and the bodies of some species (such as O. macklotti and Palophus centaurus) are covered in mossy or lichenous outgrowths that supplement their disguise. Some species have the ability to change color as their surroundings shift (B. scabrinota, T. californica). In a further behavioral adaptation to supplement crypsis, a number of species have been noted to perform a rocking motion where the body is swayed from side to side that is thought to reflect the movement of leaves or twigs swaying in the breeze. Another method by which stick insects avoid predation and resemble twigs is by feigning death (catalepsy), where the insect enters a motionless state that can be maintained for a long period. The nocturnal feeding habits of adults also aids Phasmatodea in remaining concealed from predators.
 
In a seemingly opposite method of defense, many species of Phasmatodea will seek to startle the encroaching predator by flashing bright colors that are normally hidden and making a loud noise. 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. Others will maintain their display for up to 20 minutes, hoping to frighten the predator and convey the appearance of a larger size. Some accompany the visual display with noise made by rubbing together parts of the wings or antennae.
Some species, such as the young nymphs of E. 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.
When threatened, some phasmids that are equipped with femoral spines on the metathoracic legs (O. martini, Eurycantha calcarata, Eurycantha horrida, D. veiliei, D. covilleae) respond by curling the abdomen upward and repeatedly swinging the legs together, grasping at the threat. If the menace is caught, the spines can draw blood and inflict considerable pain.[5]
A number of species are equipped with a pair of glands at the anterior edge of the prothorax that enable the insect to release defensive secretions, including chemical compounds of varying effect: from the production of distinct odors to the causing of a stinging, burning sensation in the eyes and mouth of a predator. The spray often contains pungent-smelling volatile metabolites, thought to be concentrated in the insect from its plant food sources. The spray from one species, Megacrania nigrosulfurea, is even used as a treatment for skin infections by a tribe in Papua New Guinea because of its antibacterial constituents.[6] Some species employ a shorter-range defensive secretion, where individuals bleed reflexively through the joints of their legs and the seems of the exoskeleton when bothered, allowing the blood (hemolymph), which contains distasteful additives, to discourage predators. Stick insects, like their distant relation the grasshopper, can also discharge the contents of their stomach through 
vomiting when harassed, a fluid that is considered inedible by some predators.