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How do flightless stick insects spread their populations over vast regions?

In the diverse world of entomology, stick insects stand out for a peculiar reason — their apparent ability to span vast distances despite being flightless. Their widespread presence across geographical barriers that would be daunting for most flightless species has long been a conundrum.

However, a new study led by Kobe University has shed light on this puzzle, pointing to a surprising ally in their dispersal: birds.

The stick insect dispersal enigma

The majority of stick insect species lack wings, making their extensive distribution across various terrains seem perplexing. This anomaly led to the hypothesis that their eggs might be dispersed by birds, mirroring the method many plants utilize.

The concept is simple: birds consume fruits, and the seeds within pass through their digestive systems, emerging unharmed and often at great distances from their origin.

In an experimental setting, studies focusing on Ramulus mikado, a common Japanese stick insect, confirmed that such a dispersal mechanism could indeed be possible. Yet, without any direct observation in the wild, doubt lingered about its real-world applicability.

Genetic evidence from stick insects

To address this gap, biologist Suetsugu Kenji from Kobe University and his team embarked on an ambitious project. They analyzed genetic patterns in Ramulus mikado populations, leveraging the principle of “genetic isolation by geographic distance.”

This theory posits that in species with limited mobility, genetic mutations accumulate over time, leading to a correlation between genetic differentiation and geographical distance.

Their findings, published in the Proceedings of the Royal Society B, were astonishing. While many genes showed predictable differences based on geographic distance, a select few exhibited close relations despite being separated by vast distances and formidable geographical barriers.

Kenji Suetsugu, the lead author, remarked, “Amidst a sea of limited active dispersal, we discovered identical genotypes jumping across vast distances, strongly indicating the past occurrence of passive long-distance genetic dispersal.” This discovery implies that these flightless insects may have, indirectly, taken to the skies through avian digestive systems.

Unique reproductive mechanism

This begs the question: why is such a dispersal mechanism not more prevalent among other insects? The answer lies in the unique reproductive nature of some stick insect species.

Most insect eggs are fertilized shortly before they are laid. However, certain stick insect species exhibit parthenogenesis, allowing females to produce viable eggs without fertilization. This reproductive peculiarity ensures the survival of stick insect offspring even when they embark on such perilous journeys.

Ironically, stick insects have earned their name due to their primary survival strategy: blending in with their environment to avoid predators. This is starkly different from plants that rely on their seeds being consumed and dispersed.

Implications and future research

The ramifications of this study extend beyond the life cycle of stick insects. Kenji Suetsugu emphasizes the broader significance of their findings, stating, “This result invites researchers to delve deeper into the mechanisms of dispersal in various species and challenge long-held assumptions about the fate of organisms devoured by predators.”

This intriguing research underscores the intricate and often unexpected relationships that govern the natural world. As scientists continue to unravel these complexities, we are reminded of nature’s ingenuity and resilience in the face of challenges.

More about stick insects

Stick insects, often referred to as walking sticks, are nature’s true masters of camouflage. Belonging to the Phasmatodea order, these insects stand out for their remarkable ability to blend seamlessly into their surroundings.


Native to various parts of the world, stick insects primarily inhabit tropical and subtropical rainforests. However, some species thrive in temperate regions as well. They owe their name to their uncanny resemblance to twigs, branches, or leaves, a disguise they expertly employ to evade predators.


Most stick insects showcase a predominantly herbivorous diet. They feed on leaves, favoring particular plants depending on the species. Their feeding habits often lead them to play vital roles in controlling vegetation and contributing to their ecosystem’s health.


One of the most intriguing aspects of stick insects is their reproductive versatility. While many species mate conventionally, some exhibit a unique phenomenon called parthenogenesis. In this process, females produce viable eggs without needing to mate with males, allowing rapid reproduction when necessary.

Defense mechanisms

In defense, besides camouflage, stick insects employ other tactics. When threatened, some species play dead, dropping to the ground and remaining motionless. Others might release a foul-smelling substance or make hissing sounds by rubbing their body parts together.

Kept as pets

For those keen on keeping exotic pets, stick insects make an interesting choice. They require a relatively simple habitat setup, often just a ventilated cage with appropriate foliage and regular misting. Their docile nature and easy care make them ideal for enthusiasts of all ages.

In summary, stick insects are a captivating group of creatures. Their unparalleled camouflage abilities, diverse habitats, and unique reproductive strategies make them an endless source of fascination for both scientists and nature enthusiasts alike.

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