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 Do Insects Walk on Water?
1. What is the primary scientific principle that allows some insects to walk on water?
The primary principle is surface tension. This phenomenon is caused by the strong attraction between water molecules, a property known as cohesion. This creates a thin, elastic-like film on the water's surface. Insects that can walk on water are light enough and distribute their weight effectively so that they only depress this film without breaking it.
2. What specific biological adaptations allow water striders to walk on water so effectively?
Water striders possess several key adaptations that are perfect examples of evolution in a specific habitat. These include:
- Hydrophobic Legs: Their legs are covered in thousands of microscopic, waxy hairs that repel water and trap air. This prevents their legs from getting wet and breaking the surface tension.
- Weight Distribution: They have long, slender legs (tarsi) that spread their minimal body weight over a large surface area, which reduces the pressure at any single point on the water's surface.
- Claw Position: Unlike many other insects, their claws are set back from the tips of their legs. This smart design prevents them from accidentally piercing the delicate water film.
3. What is the difference between the roles of cohesion and adhesion in this phenomenon?
Cohesion is the essential force at play; it is the attraction between water molecules that creates the strong surface tension insects depend on. In contrast, adhesion (the attraction between water and a different substance) is actively minimised. The waxy, hydrophobic coating on an insect's legs repels water, ensuring extremely low adhesion so the legs stay dry and do not break the surface film.
4. How would adding soap or detergent to water affect an insect's ability to walk on it?
Adding soap or detergent would make it impossible for the insect to walk on water, causing it to sink. Soaps are surfactants, meaning they drastically reduce the surface tension of water by disrupting the cohesive forces between its molecules. Without the strong surface film to support its weight, the insect would immediately break through the surface.
5. Why can't larger animals, such as humans, walk on water like insects can?
This is a matter of scale, specifically the relationship between weight and surface area. The upward force from surface tension is relatively weak. An insect's weight is incredibly small and is easily supported by the surface tension acting along the perimeter of its legs. A human's weight, however, is immensely greater, and the downward force of gravity completely overwhelms the maximum possible upward force from surface tension, regardless of foot size.
6. Can other creatures, like spiders, also walk on water using the same principle?
Yes, some other arthropods, most notably fishing spiders, can also walk or run across water. They employ the same fundamental principles of surface tension and hydrophobic hairs on their legs to stay afloat. Fishing spiders are generally larger than water striders and often combine their natural buoyancy with rapid leg movements to propel themselves across the water's surface.
