The physics of pricking, piercing and stabbing

Beak, spines, claws, fangs, horns … Animals have all kinds of pointed weapons and defense mechanisms at their disposal. US researchers have now developed a model to map the energy used when another animal is bitten.

Piercing is a biomechanical process that occurs in a variety of animals. From tigers to rays and snakes to insects. Even plants, such as cacti, are involved. The functions of the piercing parts vary. For example, a tiger turns its powerful, sharp fangs into prey to kill it with the mechanical force of its jaws. While venomous snakes are present, the sting mainly serves to inject a lethal substance.

Another interesting example is the oval checker for parasitic wasps, mailed by postdoc Pingyang Zhang of the University of Illinois Urbana-Champaign, who developed the model with Philip Anderson. “These wasps use their stingers or ovipositors to lay their eggs in the larvae of other insects. Sometimes these larvae are buried deep in fruit or even wood. Therefore, parasitic wasps have incredibly long, thin needles that reach several times their body length. They can use it to burrow. into the wood to reach the larvae.”

The parasitic wasp can direct its long ovaries into the wood

The researchers have now attempted to capture this wide range of punching techniques into a mathematical model. With this they hope to be able to better compare different biological piercings and investigate how physical laws affect the optimal shapes of beaks, spines, teeth and stings.

The model could also help engineers develop new technologies to efficiently penetrate materials or resist punctures, according to Zhang’s emails. For example, medical needle designers are researching the flexible ovary of a parasitic wasp. The researchers published their model in the professional journal in October Royal Society Interface Magazine.

In their model, the researchers take into account the different shapes and sizes of piercings, which often depend on the function. “For example, the fangs of venomous snakes can be described as a hollow, curved structure with a channel or groove for venom,” Zhang explains. “While porcupine feathers are straight. The long egg depots of parasitic wasps consist of several structures that allow the stinger to change its shape during the sting.” This allows the wasp to steer in a targeted manner.

Soft breast skin

The model also includes what the prey or enemy material is made of. The skin of soft mammals requires a different puncture technique than prey with hard scales. Penetration speed also plays a role. This means that young animals can still penetrate solid or solid matter if the speed increases. You see this, for example, in jaw-trap ants, which clap their jaws together at a speed of more than 100 km / h.

Shape, size, speed, and materials together determine how much energy is involved in a bite or sting and thus how deep the teeth or stings can penetrate. The power is distributed over different hole steps. First, the piercing tool hits the victim. If this is done with sufficient energy, a break in the skin or surface occurs. There must be enough energy left to overcome the resistance of the base material and penetrate deeper.

At the same time, elastic energy accumulates in the perforated material, which ‘pulls back’ and thus slows down the perforation. According to the model, the deeper the penetration, the more difficult it is to overcome this resistance and elastic energy. In some cases, the material forces the punch tool to retract.

shoot arrows

The researchers confirmed these predictions with an experiment in which they fired arrows at different points and speeds at cubes of gelatin with a density similar to tissue. The arrows were actually found to reach a limited depth and in some cases an arrow was ejected by the elastic energy of the gelatin cube.

According to the researchers, the model is not out yet. For example, it cannot yet accurately predict how skin penetration differs from muscle and fat penetration. Ultimately, the goal is to explain which teeth or spines with the energy caused a particular wound.

Leave a Comment