Walking sticks, also known as stick insects or phasmids, are insects renowned for their remarkable ability to blend seamlessly into their surroundings. Belonging to the order Phasmida, these masters of disguise mimic twigs, branches, or leaves, making them incredibly difficult for predators to spot. More than 3,000 species exist globally, found on every continent except Antarctica, primarily thriving in temperate and tropical regions.
Measuring Their Length: Typical and Record Sizes
The length of a walking stick is measured by its body length, which excludes the legs and antennae. Common walking stick species range from about 1 to 12 inches (2.5 to 30 centimeters) in length. For instance, the common walkingstick (Diapheromera femorata) found across North America averages about 3 inches (75 mm) for males and 3.7 inches (95 mm) for females. Another North American species, the giant walkingstick (Megaphasma denticrus), can reach up to 7 inches (17.8 cm) in females.
Record-breaking lengths are observed in species, particularly those found in Southeast Asia. Phobaeticus chani, also known as Chan’s Megastick, from Borneo, set a previous record. One specimen measured 14 inches (35.7 cm) in body length and 22.3 inches (56.7 cm) with its front legs fully extended.
The current record for the world’s longest insect is held by Phryganistria chinensis Zhao, discovered in China. A specimen from the Insect Museum of West China was certified by Guinness World Records at 25.2 inches (64 cm) with legs fully extended, and a body length of 15 inches (38.2 cm).
Factors Influencing Their Ultimate Size
An individual walking stick’s size is influenced by biological and environmental factors. Size is species-dependent; some species are inherently larger than others due to their genetic makeup. Tropical regions, for example, tend to host the largest and most abundant walking stick species.
Sexual dimorphism, a difference in size between sexes, is a factor, with females often growing larger than males within the same species. For instance, female common walkingsticks are notably larger than their male counterparts. This size disparity is influenced by growth trajectories, with females potentially being more sensitive to environmental conditions.
The availability and quality of food also play a role in their size. A consistent and nutritious diet supports optimal growth, while nutritional stress can limit an individual’s potential size. Environmental conditions such as temperature and humidity can also affect growth rates. A stable environment allows these insects to develop fully, as it reduces the need for energy-intensive defensive behaviors.
The Molting Process: How They Grow
Walking sticks increase in size through a process called molting, or ecdysis, which involves shedding their rigid outer covering, the exoskeleton. As an insect grows, its exoskeleton does not expand, necessitating periodic shedding to accommodate its increasing body mass. Each developmental stage between molts is known as an instar.
Before molting, the insect separates its old cuticle from the underlying epidermal cells. A new, larger exoskeleton begins to form underneath the old one. When ready, the walking stick hangs upside down, and muscular contractions, along with the intake of air or water, cause its body to swell, splitting the old exoskeleton along lines of weakness. The insect then extracts itself from its old skin.
Immediately after molting, the new exoskeleton is soft and vulnerable, making the insect susceptible to predators. The walking stick expands its body, often by pumping hemolymph (insect blood) or air, before the new cuticle hardens and darkens. Nymphs sometimes consume their shed skin. Walking sticks undergo multiple molts to reach their full adult size.