Microstructures Protect From Damage

brown and green dragonfly perched on brown wooden stick in close up photograph during the daytime

Biological Strategy

Alexandra Ralevski

Image: Kaushik Murali / Unsplash / Free non-commercial use

Attach Temporarily

Living systems must sometimes, temporarily, stay in one place, climb or otherwise move around, or hold things together. This entails attaching temporarily with the ability to release, which minimizes energy and material use. Some living systems repeatedly attach, detach, and reattach for an extended time, such as over their lifetimes. Despite being temporary, these attachments must withstand physical and other forces until they have achieved their purpose. Therefore, living systems have adapted attachment mechanisms optimized for the amount of time or number of times they must be used. An example is the gecko, which climbs walls by attaching its toes for less than a second. Other examples include insects that attach their eggs to a leaf until they hatch, and insects whose wings temporarily attach during flight but separate after landing.

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Modify Position

Many resources that living systems require for survival and reproduction constantly change in quantity, quality, and location. The same is true of the threats that face living systems. As a result, living systems have strategies to maintain access to shifting resources and to avoid changing threats by adjusting their location or orientation. Some living systems modify their position by moving from one location to another. For those that can’t change location, such as trees, they modify position by shifting in place. An example of an organism that does both is the chameleon. This creature can move from place to place to find food or escape predators. But it also can stay in one place and rotate its eyes to provide a 360-degree view so that it can hunt without frightening its prey.

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Microhairs on the head and neck of the dragonfly create friction to temporarily arrest the head and protect it from damage.

Most insects have multiple points of attachment between their head and neck. This keeps the head stable and protects it from damage, but it limits the range of motion, reducing visibility. In species that need a wider visible area—such as hunters like dragonflies and damselflies—the head and neck are attached only at a single point. Although this allows for a wider range of motion, this arrangement also makes the head more vulnerable to damage when the insect moves suddenly. To help keep its head more stable, the dragonfly has a “head-arresting system,” which allows the head and neck to join temporarily, keeping the head in place.

The head-arresting system is comprised of thousands of fixed hairs, known as microtrichia, located on the back of the head and upper part of the neck. The hairs have complementary shapes that allow them to fit together, and each pair of interlocking hairs creates a small amount of friction as they slide past one another. The cumulative effect of thousands of hairs rubbing against each other adds up to a significant amount of friction, allowing the dragonfly to hold its head stably in place. The attachment is easily reversible if the dragonfly uses enough force to pull its head away from the neck, allowing the insect to repeatedly and stably attach the head and neck.