Indian Walking Stick

Pest Notes: Introduction

Walking stick insects, belonging to the insect order Phasmatodea, are mostly tropical insects that are considered entomological curiosities because of their remarkable mimicry of twigs and leaves. Several species are popular in the pet trade and for grade school demonstrations. This has caused the Indian walking stick insect, Carausius morosus, to become established in many parts of the world.

The Indian walking stick is native to southern India, but the precise time of its establishment in California is unknown; the first official finding occurred in San Diego County in 1991 and soon after in San Luis Obispo County. The most northerly extent of its current range in California is Humboldt County with verified finds in 2021. Indian walking stick populations are confined to the coastal regions of California where the mild conditions allow for their survival in the wild. There has been an increase in observations of Indian walking sticks in recent years, particularly the San Francisco Bay Area, but reports of Indian walking stick damage in landscapes have been less frequent over the same time period.

The establishment of Indian walking sticks in California landscapes has occurred because of their escape from captivity or through introduction of their eggs. Indian walking stick females produce viable eggs without mating and, in captivity, broadcast them throughout their cages or containers where the eggs become co-mingled with their droppings (frass). The eggs are difficult to distinguish from frass and so are easily overlooked and thrown away in the process of cleaning the cage. Owners of walking stick insect pets must be responsible for understanding the biology of these organisms and caring for them properly.

Identification and Biology

The adult Indian walking stick is 2 3/4 to 4 inches long, wingless, and usually brownish with a long, thin body and legs. It can retract its legs seamlessly alongside its body, enhancing the insect’s sticklike appearance. The forelegs project forward, adding to the overall length of the insect.

Indian walking stick eggs look like seeds. Each egg is ovoid in shape and grayish brown in color, with a small, buff-colored cap (operculum) on one end through which the young insect emerges. The eggs are similar in size and color to the frass these insects produce, but the frass is rough in texture. Juveniles, called nymphs, develop through five molts; they called an instar between each molt. Nymphs progressively grow larger each time they molt but have similar coloration to the adults; therefore it may be difficult to distinguish larger nymphs from adults.

Adult females can live for several months and produce several hundred eggs during their lifetime. Eggs hatch in 10 to 12 weeks at room temperature. The five nymphal instar stages take 4 to 6 weeks to complete before the insect reaches adulthood. No rigorous studies of temperature-dependent developmental durations or reproduction have been published for this species. Most knowledge has been gained from their use in the pet trade.

Indian walking sticks reproduce mainly asexually (parthenogenetically), with females haphazardly dropping eggs while they feed or rest. Males of this species are rare; nothing is known regarding the conditions required to produce them. Females frequently feed and move through foliage at night but also can be observed feeding throughout the day. The conditions along the coast of California are mild enough for these tropical species to survive through the winter, although they do so mainly in the egg stage. Thus, most observations of activity and damage take place during the spring when nymphs emerge from over-wintered eggs and begin feeding. Multiple generations occur during the summer, and both nymphs and adults may be observed well into November or until the first frost.

Stick insects exhibit crypsis, a combination of color, shape, and behavior that helps them blend into their environment, thus avoiding detection by predators. They are easily mistaken for twigs or sticks, hence their common name. When stick insects move through the foliage, they typically do so very slowly and with swaying movements that mimic the effects of wind on the plant. When disturbed, the insect retracts its legs and remains perfectly still, even when handled. Only when aggressively handled will the insects display yet another phenomenon—a warning coloration: if the insect is in danger of being harmed, it will splay its forelegs to reveal bright red patches on its inner femora near the attachment points to the body. This color can startle predators, giving the insect a chance to escape. When a stick insect isn’t on a feeding site, such as walking on bare ground or poised on a man-made structure, they become easily evident, and due to their large size, can alarm some people.

Indian walking stick egg survival has not been studied in California. The eggs in their native home are attractive to grain-feeding ants that mistake them for seeds and cart them back to their nests but never feed on them. Since the eggs are broadcast into the environment, the ants play a role in the egg’s survival by bringing them into the nest, where they remain undisturbed until hatching.

A few walking stick species are native to California including the western shorthorned walking stick, Parabacillus hesperus, the gray walking stick, Pseudosermyle straminea, and species in the genus Timema. All these species feed primarily on grasses and scrub brush, mostly woody shrubs, in dry, wild areas and have not been reported as pests in landscapes. Adult females of the Indian walking stick can be readily distinguished from these species by the red markings at the base of their front legs.

Damage

Indian walking sticks feed on a wide variety of plant species in California including but not limited to azalea, bramble, camellia, geranium, hawthorn, hibiscus, ivy, jasmine, oak, privet, pyracantha, rose, and some common garden vegetables.

The worst damage is typically seen in the springtime when nymphs are hatching from eggs and feeding on new flush growth of many plant species in landscape settings. They feed aggressively on small-leafed varieties of ivy and privet. Nymphs and adults feed heavily on the margins of mature leaves, creating a tattered appearance, or fully consume smaller, tender leaves. Populations usually develop unnoticed until significant feeding takes place. Damage reports in landscapes have been spotty and inconsistent from year to year on the Southern and Central coasts of California. The most frequent complaints arise from residents when they encounter walking sticks on windows, doors, or even inside homes on warm summer nights.

Management

Indian walking sticks usually are mostly a nuisance in the landscape, although in some years and in some locations they can seriously defoliate plants and cause damage to valued specimens.

Prevention

Do not release Indian walking sticks or other exotic insects into landscapes or wild areas. If you are keeping these species as pets, when cleaning the cage put the debris into a bag, close the bag securely, and for best results, place it in a freezer for a week before throwing it in the trash. Do not toss loose debris outside, as it might contain eggs or the insects. If you no longer care to raise Indian walking sticks, dispose of the entire contents of the cage including live insects and all debris as described above.

Biological Control

No biological agents have been released for controlling the Indian walking stick. While it is assumed that generalist predators feed upon them when encountered, no definitive studies have been conducted.

Mechanical Control

Removing stick insects by hand from outdoor plants and discarding them in the trash after freezing can reduce populations over time and reduce evidence of feeding; however, finding them may be difficult due to their cryptic nature.

Chemical Control

There is no research on the effectiveness of pesticides against walking sticks. Generally, pesticide applications are not recommended, since they might kill beneficial insects occurring in the landscape.

Resources

• About Pest Notes
• Glossary
• WARNING ON THE USE OF PESTICIDES
• List of other Pest Notes

Publication Information