How insects walk (making the most of insect legs)

(1) Basic structure of thorax and feet

The legs are the locomotion organs of insects. Insects have 3 pairs of legs, one pair each on the prothorax, mesothorax and metathorax, which we call forefoot, middle foot and hindfoot accordingly. Each foot is composed of basal segment, trochanter, leg segment, tibia, tarsal segment and pretarsal segment. The basal section is the basemost section of the foot, which is thick and short. The trochanter is often closely connected to the leg joint and inactive. The leg segment is the longest and thickest segment. The fourth segment is called the tibia, which is generally slender and has rows of spines. The fifth segment is called the tarsal segment, which is generally composed of 2-5 subsegments; it is used to facilitate walking. There are two hard and sharp claws at the end of the most distal segment, which can be used to grab objects. There is often a sac-like suspension pad between the two claws, also called a claw pad, which can be used to grab objects. A secreted adhesive substance that adheres to the surface of smooth objects. Sometimes the paw pads become needle-like, called interclaw processes. Many insects have some sensory organs on the surface of their tarsus and suspension pads, which can sense the contact with objects and use this feeling to decide their actions. Some insects also have olfactory sensory organs on the talons of their front legs, such as flies and moths, which can use their front legs to determine the presence of available food.

(2) Types and functions of thorax and feet

Different types of insects have different habits and live in different places. In order to adapt to different living environments, the shape of the foot has undergone great changes, and its function has gradually developed from a single walking function to an organ with multiple functions (pictures of various feet).

① Walking legs: Although the walking bugs that run underground have wings, they are no longer good at flying. In order to adapt to the needs of their lives, after a long period of evolution, their six legs have become thin and long, and they can run very fast. This type of foot is called a walking foot. Of course, the most basic and common among insects are walking legs. Their appearance is slender and their segments have not undergone significant changes. They are most suitable for walking, such as ladybugs, walking bugs, beetles, etc.

②Jumping feet: Insects such as locusts, crickets, flea beetles, and flea beetles are very good at jumping; their hind foot leg segments are enlarged and contain well-developed muscles, which can control the flexion and extension of the tibia segments and produce jumping behavior. Catching these insects requires quick hands and eyes, otherwise they will disappear without a trace in an instant. The high jump champion among insects is none other than fleas. They can jump to a height that is more than 100 times their body length. It is conceivable that if humans can jump 100 times their own height, then the existing world high jump record is simply not worth mentioning. .

③ Predatory feet: Predatory insects such as mantises and bug bugs are a type of beneficial insects that do not eat crops and live exclusively by preying on small animals. They hatch from eggs with a pair of knife-shaped front feet. The base section of this kind of forefoot is extended, and there is a groove on the ventral surface of the leg section. The tibia section can be folded into the groove of the leg section. The leg section and intestine section are often equipped with sharp spines, which are powerful weapons for catching prey. When it captures prey, it can use its leg segments and tibia segments to hold the food it wants to eat, and then use the sharp spines on the inside of the tibia segments and the outside of the leg segments to tear the prey into pieces and eat it. This type of foot is called a capture foot.

④ Digging feet: Molecules live in the soil, dig tunnels, and eat the roots and stems of crops. So how do they get into the ground? It turns out that their front feet are thick and strong, and there are several large teeth on them. , like a shovel specially designed for digging soil, it is very convenient to dig up soil. This kind of foot is called open and stubborn foot.

⑤Powder-carrying feet: Bees are busy every day, shuttling back and forth among flowers to collect pollen and nectar. What do they use to carry it? After long-term adaptation, the tibiae of their hind legs are specialized to be wide and flat, surrounded by long hairs, which are specially used to carry pollen, and are called pollen baskets. Its basal segment also has a special purpose. It is larger than the basal segment of ordinary insects. There are 10 to 12 rows of bristles on the inside, which are used to comb the pollen scraped on the body. When the hard work of collecting is over. Swarms of bees returned laden with pollen. This kind of foot is called pink foot.

⑥Swimming feet: Insects living in the water such as dragon lice and stink bugs can capture fish fry and use them as food, which is a major hazard to fisheries. Fish swim fast enough in the water, how can they catch up with them? It turns out that the bodies of dragon lice and frog bugs are nearly streamlined, much like a fast submarine. The middle and hind feet are long and flat, and there is a row of neat long hairs on the inward side. These four legs are like four rowing boats. The paddle makes swimming very fast. This kind of foot is called swimming foot.

⑦ Clutching feet: For example, the forefoot appendages of male dragon lice are particularly enlarged and have sucker-like structures on them, which are used to hold the female during mating. This type of foot is called a clinging foot.

⑧ Climbing feet: Lice that live on hair have only one tarsal segment, and the last segment is a large hook-shaped claw. The tibial segment is hypertrophic and has a finger-like protrusion on the outer edge. When the claw is bent inward, the tip can be in close contact with the finger-like protrusion at the end of the tibia, forming a pincer-like structure that can firmly clamp the host's hair. This type of foot is called a climbing foot.

The feet also have many other wonderful functions: the end of the tibia of the forefoot of some wasps and the base of the first tarsus jointly form a horn cleaner, which is specially used to clean the antennae and remove things stuck to the antennae; the ends of the feet of flies form claw pads , the pad is filled with blood, and the depression below is like a vacuum cup. There are hairs on the pad that can secrete mucus, so flies can walk on the smooth glass plate without slipping, and can even move freely while hanging upside down on the ceiling. The "ears" (hearing devices) of some insects grow on the front feet. For example, the favorite cricket uses the eardrum hearing device on the front feet to receive the call of the opposite sex. The appendages of the legs of butterflies and flies also have the function of sensing taste. The byssal ant insects that live under the dark bark and moist moss on rocks use their feet to make silk and weave them into tunnel-like nests, where they live and reproduce. Therefore, their feet have a special structure. The first tarsal joint of the forelegs of the byssal ant is particularly enlarged. It contains more than 110 spindle-like silk glands, which look like a textile machine. Each silk gland is round, and there is a hole in the wall of the silk gland. There are layers of cell nuclei, but there is no obvious cell boundary, so the silk gland is a syncytial gland. Each gland cavity is filled with secretions directly transformed from the protoplasm. The secretions flow out along the flat cell gland ducts, and the gland ducts open at The tip of an elongated epidermal protrusion. When the liquid secretions are discharged from the glandular ducts, they become the threads used to weave the tunnels when they come into contact with the air. The silk-making glands are periodically renewed during shedding. Although byssus ants shed their skin several times in their lives, their silk-making function on their feet does not diminish.

In addition to adults, many species of insects also have strong ability to crawl on their feet. When armyworms occur in large numbers, their larvae often crawl in groups in one direction in search of food. Wherever they go, the seedlings are completely empty, and they can often move hundreds of meters in one night. The same phenomenon can also be seen when cutworms occur severely.

Insect feet are not only capable of crawling, jumping, catching, and digging, but some insect species also have amazing pulling and grasping powers. A small beetle weighs only 6 grams, but the weight of the object it drags with its feet (on a light four-wheeled car) is 1.093 kilograms, which is 181 times greater than the weight of this small beetle. A strong horse weighing 700 kilograms can only drag 3.5 tons of cargo on a good road, which is only five times its body weight. A person's traction force is roughly only 5 times of body weight. However, an ant can easily put food or nesting materials exceeding 1400 times the volume and weight into its nest. A mature earwig weighs only 0.5 grams. If a 170-gram empty toy car is tied to its body with a string, it can be easily dragged around with its three pairs of legs. When the items on the car are increased to 265 grams, it can still barely drag it. If the weight of this earwig (0.5 grams) is taken and the total weight of the car it is dragging and the things inside is removed, After adding four and five numbers, you can get an unprecedented number - 530 times.

Insect feet are very small, so it is difficult to imagine that they can use their fragile claws to grab heavy objects. In order to prove the gripping power of insect feet, someone once conducted an experiment like this: using a thread on a dragonfly Wrap a circle around its chest, hang it up, and then put a rough weight on it for it to grab. It was found that the dragonfly can grab an object 20 times its body weight for 10 minutes. Using the same method for testing, the mantis can grab a weight of 324 grams, which is 53 times larger than its body weight. The giant earwig can pick up a weight of 52 grams, which is 104 times heavier than its body weight.

Knowing the adaptation of insect legs to the natural environment and seeing the shapes of different insect legs, you can roughly know the environment in which certain species of insects live. At the same time, the internal and external structures of insect feet are studied, and their pulling and grasping functions are explored, which can be applied in bionics.

(3) How do insects walk?

We humans have only two legs, and we walk by alternating forward and backward movements of our legs. So how do insects arrange their six legs when walking? It turns out that insects have their own idea: they walk in groups of three legs, that is, the front and rear feet on one side and the midfoot on the other side form a group. This forms a triangular support structure. When these three legs are placed on the ground and pushed back, the other three legs are lifted forward to prepare for rotation. Let's take a closer look at how the three legs in a group work together: the front legs use their claws to fix objects and pull the insect forward, the middle legs are used to support and lift the body on their side, and the hind legs push the insect forward. , and at the same time make the insect body turn. This way of walking allows the insect to stop anytime and anywhere because its center of gravity always falls within the tripod. Not all adult insects use six legs to walk. Some insects have specialized front legs that have other functions or degenerate, and walking is mainly completed by the middle and hind legs. The most familiar one to everyone is the mantis. We can often see the mantis's pair of pincer-like front legs raised high in front of its chest, while its four rear legs support the ground to walk. The insect's maximum walking speed is about 3 miles per hour, which is quite enough for its small body.Soon.

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