Walking sticks, also known as stick insects or phasmids, are remarkable insects renowned for their extraordinary camouflage, allowing them to blend seamlessly with their environment. They often resemble twigs, branches, or leaves, making them difficult to spot. Their unique appearance often leads to questions about their potential harm to humans or plants. This article explores common questions regarding their safety.
Assessing Risk to Humans
Concerns about walking sticks posing a threat to humans are largely unfounded, as most species are not equipped with venom, fangs, or stingers. While they possess mandibles, bites on humans are exceptionally rare and typically do not break the skin or cause pain. Some larger stick insect species might use their spiny legs to pinch if they feel threatened, but this action is generally harmless and causes no significant injury.
Most walking stick species are not considered toxic if touched, meaning casual contact does not pose a health risk. Consuming a walking stick would typically result in only mild nausea and is not life-threatening. Their primary defense mechanism involves remaining still and camouflaged, relying on their appearance to avoid detection by predators.
An exception exists with the Two-striped Walking Stick, Anisomorpha buprestoides, found in the southeastern United States. This species can deploy a defensive chemical spray from glands near its head or thorax when disturbed. The spray, a mixture of irritating terpenes, can be aimed up to two feet away. If this substance contacts the eyes, it can cause intense burning, temporary blindness, conjunctivitis, or inflammation of the cornea. These effects are usually short-lived and do not result in permanent damage. Skin irritation is also possible upon contact. Should exposure occur, immediate and thorough rinsing of the affected area with water is recommended.
Impact on Plants and Gardens
Walking sticks are herbivores, primarily feeding on leaves. They feed on a variety of plants, including common trees and shrubs like oak, hazel, blackberry, privet, and ivy. These insects typically feed at night, consuming leaf tissue and sometimes leaving behind only the veins, a process known as “skeletonizing.”
In most natural settings, walking sticks do not pose a significant threat as agricultural or garden pests. Their populations are usually dispersed, and their feeding habits rarely cause widespread damage to crops or ornamental plants. Home gardeners are unlikely to experience extensive plant defoliation from these insects due to their generally low numbers.
There are rare instances where certain species, such as the Indian walking stick (Carausius morosus) or the Northern walkingstick (Diapheromera femorata), can cause localized defoliation, particularly in non-native environments or during population outbreaks. While this can sometimes affect the health of trees, plants in temperate climates typically recover from such feeding. More substantial defoliation and tree damage are primarily observed in tropical regions where walking stick populations can be abundant.
Walking sticks also contribute to the ecosystem as primary consumers. Their feeding activity can sometimes encourage new plant growth by pruning foliage. Additionally, their droppings help fertilize the soil. These insects serve as a food source for a range of predators, including birds, reptiles, spiders, rodents, and bats, supporting biodiversity. Their eggs are even dispersed by other organisms, such as ants and birds, integrating them into the natural cycle.