What Allows Insects to Walk on Water Surface Tension and Hydrophobic Legs
Why Insects Can Walk on Water?
Insects get a total of 6 legs that are located on the pro-, meso- and metathorax, such as a pair of fore, mid and hind legs. Every leg is divided into six segments, that are called coxa, trochanter, femur, tibia, tarsus and post-tarsus, beginning from the top of the leg. They are all connected by the same muscles. These compartments, instead, are called 'tarsomeres'.
Usually, the post-tarsus is fitted with pulvilli, which are smooth or hairy pads used for adhesion. Although the femur and tibia are typically the largest leg segments, depending on the lifestyle of the insect, there is a great deal of change. Walking or running insects, for instance, have well-developed femur and tibia on both legs, such as the cockroach or stick insect, whereas Hind femur and tibia have disproportionately sized jumping insects such as the grasshopper, giving them the ability to leap great distances.
Swimming insects generally have tarsi and tibia bearing long hair fringes used to propel them through the water, and fore tibia has been largely changed by digging insects to allow them to dig effectively.
In order to get the momentum required to propel the body forward, it is very important that the insect is capable of having a firm grip on the substrate. Claws on the insect's feet that can stick to even the slightest roughness on the substrate can accomplish this anchorage.
Pads covered in fine hair are lubricated on fully smooth surfaces, and the close-range molecular forces between the hair and the surface work to anchor the insect.
While insect leg anatomy varies widely, roboticists are most interested in the legs of insects such as cockroaches (Order Blattodea) and stick insects (Order Phasmatodea), as these insects are 'flying' insects. For hexapod robot use, the walking mechanisms of these orders have been researched and mimicked.
How Do Insects Walk on Water?
Through the contraction and relaxation of thoracic muscles attached to the base of the leg and the cuticle, insects may walk. First of all, these muscles act on the base of the leg, and the contraction is then transmitted through the leg through the internal leg muscles, causing the leg to stretch or flex. Two gait forms, tripod gait and metachronal wave gait, are often used by insects for walking. Three legs are in contact with the ground at all times during the tripod gait, including the fore and hind legs on one side and the middle leg on the other side. While the stable legs drive the body forward to provide protection, the remainder of the legs swings forward. As the legs establish a tripod shape, this mechanism of walking is called 'tripod gait'. As the insect's centre of mass is still inside the tripod, this gait is very stable.
Metachronal or wave gait involves only moving one leg at a time, starting on one side of the insect with a hind leg, then on the same side with the middle leg, then the foreleg, then the same on the other side. This gait is slower than the gait of the tripod but more stable, as during each leg movement there are more legs in contact with the ground.
Insects have a range of options that they can use to allow them to travel at greater speeds.
They're able to:
Raise the frequency of leg movements
Enhance their length of stride
Lift two or four of their legs above the substrate and move to bipedality of quadruped or hind leg.
The centre of mass of the insect also falls outside the tripod in both of these instances, making it very unstable. The insect isn't any longer 'statically' stable, and must use 'dynamic' techniques of stability to ensure that it does not lose balance. In order to stay balanced, dynamic stability includes using muscles. Lately, engineers also started utilizing insect gait systems in their robots since they have found that hexapod robots are very stable, like their biological counterparts. Usually, these robots just use tripod gait, but even the metachronal wave gait and a variety of other forms of gait not commonly used in insects can be used.
Why Can Insects Walk on Water Surface Tension?
Due to a phenomenon known as surface tension, insects can move on water. This is basically a water property (or any liquid) that enables an external force to be resisted. Water molecules create bonds between certain molecules and air molecules on each side form quite a deeper bond than molecules without molecules. However, since insects are fragile and do not have sufficient force to break, they can theoretically walk on water. One of the best examples of this process is seen in water striders named insects.
In fact, insects are so tiny that even dropping from a 10-storey building does not pose a risk of injury. However, an insect has to face many other threats, such as being crushed, consumed or predated. Besides these risks, the difference between life and death may also be surface stress. For insects, water appears to behave like fast sand. This induces the insect to get trapped and die through drowning inside the water bubble. And if an insect had to swim to the surface, forcing itself out of the bubble is not in its body.
Some insects have a covering made of keratin to withstand this, which helps the water to only slip away. Therefore, even though it rains, the raindrops would just fall on the surface of the bug and just roll off.
FAQs on How Insects Walk on Water in Biology
1. How do insects walk on water?
Insects walk on water by using the high surface tension of water, which acts like a thin elastic film that supports their weight. Surface tension is created by cohesive forces between water molecules.
- Water molecules stick together due to hydrogen bonding.
- This creates a strong surface layer at the top of the water.
- Lightweight insects distribute their weight over long, hydrophobic legs so the surface does not break.
2. What is surface tension in biology?
Surface tension is the tendency of water molecules to stick together at the surface, forming a tight, elastic-like layer. In biology, this property is important for processes such as water transport in plants and allowing insects to walk on water.
- Caused by cohesion between water molecules.
- Strongest at the air–water interface.
- Supports small organisms like water striders.
3. Which insects can walk on water?
Insects such as water striders (Gerridae), pond skaters, and some fishing spiders can walk on water. These organisms are specially adapted for life on the water surface.
- They have long, slender legs.
- Their legs are covered with hydrophobic hairs.
- They are lightweight, preventing the water surface from breaking.
4. Why don’t water-walking insects sink?
Water-walking insects do not sink because their weight is balanced by the upward force created by surface tension. The water surface bends under their legs but does not break.
- Their legs spread their body mass over a large area.
- Hydrophobic (water-repelling) surfaces prevent wetting.
- The downward force is less than the surface tension force.
5. What adaptations help insects walk on water?
Insects that walk on water have structural adaptations that enhance buoyancy and surface support. The most important adaptation is their hydrophobic legs.
- Legs covered with microscopic, water-repelling hairs.
- Long and widely spaced legs for weight distribution.
- Light body mass to reduce pressure on the surface.
6. How do hydrophobic legs help insects stay on water?
Hydrophobic legs help insects stay on water by repelling water and preventing their legs from becoming wet and sinking. These legs are coated with tiny hairs that trap air.
- Create a water-repellent surface.
- Increase buoyancy by trapping small air pockets.
- Maintain the integrity of the surface tension layer.
7. Is walking on water due to buoyancy or surface tension?
Walking on water is mainly due to surface tension, not buoyancy. Buoyancy depends on water displacement, while surface tension depends on cohesive forces at the surface.
- Buoyancy: Upward force from displaced fluid.
- Surface tension: Elastic-like surface caused by cohesion.
- Water-walking insects rely primarily on surface tension.
8. How do water striders move across water?
Water striders move across water by rowing with their middle legs while balancing on their front and hind legs. This motion creates small ripples that propel them forward.
- Middle legs push backward against the water surface.
- Front legs detect vibrations from prey.
- Hind legs provide stability and steering.
9. What role do hydrogen bonds play in insects walking on water?
Hydrogen bonds between water molecules create the strong cohesive forces responsible for surface tension. These bonds hold the surface layer tightly together.
- Each water molecule forms multiple hydrogen bonds.
- This creates a net inward force at the surface.
- The resulting tension supports lightweight insects.
10. Can all insects walk on water?
Not all insects can walk on water; only specially adapted species can use surface tension effectively. Most insects lack the necessary structural features.
- Absence of hydrophobic leg structures.
- Body weight too heavy for surface tension support.
- No behavioral adaptation for surface locomotion.
