The insects of the order Phasmatodea, commonly known as walking sticks, are masters of camouflage and elusive herbivores. Their primary defense is crypsis, a blend of morphology and behavior that allows them to perfectly mimic the twigs, stems, and leaves of their host plants. This reliance on camouflage means that while walking sticks are abundant, they are rarely seen.
Primary Predators: Birds and Small Mammals
The most active, generalist predators that regularly consume walking sticks are birds and small insectivorous mammals that hunt by sight or scent. Birds, such as American robins and crows, are known to prey on species like the Common American Walkingstick (Diapheromera femorata). These avian hunters often use an investigative peck on anything that appears to be a twig, which can reveal a stationary walking stick.
Specialized nocturnal predators, particularly bats, are also highly effective hunters. Echolocation, the method bats use to navigate and locate prey, bypasses the insect’s visual camouflage entirely. Small mammals like shrews and rodents on the forest floor will also consume walking sticks that fall or lay their eggs in the leaf litter.
Opportunistic Hunters: Reptiles, Amphibians, and Invertebrates
A different group of predators encounters walking sticks through chance or ambush rather than active pursuit. These opportunistic hunters include reptiles, amphibians, and large predatory invertebrates. Lizards, such as geckos and chameleons, often sit and wait on vegetation, making them likely to encounter a slow-moving walking stick.
Amphibians like frogs and toads will also consume walking sticks, typically when the insects venture to lower branches or the ground. Large predatory invertebrates, such as tarantulas, orb-weaver spiders, and praying mantises, are significant threats, especially to smaller nymphs. These predation events often occur during vulnerable periods, such as when the walking stick is molting and temporarily immobile.
Evasion Strategies and Specialized Defenses
When the primary defense of crypsis fails, a suite of secondary defenses is deployed. One common tactic is thanatosis, or playing dead, where the insect drops from its perch and remains rigid and motionless. Another specialized mechanism is autotomy, where a nymph can voluntarily shed a leg when grabbed by a predator. This sacrifice allows the insect to escape, and the lost limb can be regenerated over subsequent molts.
Many species have evolved potent chemical defenses to deter an attack. The Two-Striped Walkingstick (Anisomorpha buprestoides) is a notable example, capable of forcefully spraying a noxious, milky-white fluid from specialized glands near its head. This secretion contains irritating compounds that can cause temporary pain or transient blindness in small predators. Other species, such as the Giant Spiny Stick Insect (Eurycantha calcarata), release foul-smelling or distasteful substances. For walking sticks with wings, a sudden startle display is used, involving flashing bright, contrasting colors on the hindwings to momentarily confuse a predator before dropping to the ground.