The Wasp: Physical Analysis of Body and Movement 

Andrew Habelrih, Eliot Azar, Malak Zakaria

Abstract

This article provides an analysis of the physical principles behind wasp , body structure and its defense mechanisms. The flight of the wasp is defined by the clap-and-fling phenomenon found in many insects, which allows them to generate lift more efficiently and helps energy conservation. The environmental factors that influence the flight of a wasp are wind direction, which affects it via the drag incurred on its body; humidity, by changing the properties of the air surrounding the wasp; and atmospheric temperature, due to the ectothermic nature of the wasp. The wasp’s morphology is analyzed through the structure of their compound eyes and the adhesive properties of their legs which function with a single muscle. These are two adaptations which actively help them thrive in their home environments by helping them spot their predators more efficiently, helping them stabilize themselves during flight, and by being able to stick onto various surfaces. In addition, the defensive mechanisms of the wasp are also presented through the power behind their mandibles with their cross-closing motion and their stinger. The structure of ovipositors for certain parasitic wasps allows it to extend to 12 times its body length to reach deep inside of their host. This study examines the evolutionary biomechanical adaptations of this super organism to better understand their behavioral interactions with prey, against predators, and within their own colonies.  

Introduction 

Insects, how tiny they may be, have astonishing abilities, ranging from extraordinary sensory capabilities to tremendous movement mechanisms. Their organs having evolved differently than mammals, they can have very unfamiliar interactions with their environment. Particularly, wasps have many useful skills linked to various aspects of their body. Wasps have a very complex flight mechanism that reflects environmental factors such as air currents, temperature, air density, or humidity. Various wing shapes can be found amongst wasp species, creating a large variety of flight patterns. Wasps’ peculiar compound eye structure allows impressive visual abilities despite its structural resolution limitations. Indeed, this eye structure is optimized to their movements in order to maximize resolution when necessary. Wasps also have an impressive adhesive capability on almost every surface, thanks to impressive leg features such as adhesive hair-like structure called setae or adhesive pads called arolium. Their sophisticated yet effective defense mechanisms, such as their mandibles and their stinger, allow them to capture prey and deter threats, thus making them efficient predators. These various characteristics can be approached with physical phenomena to explain and understand their functioning. These complicated abilities are the result of millions of years of and allow wasps to thrive as a species. 

Flight 

The wasp can achieve flight due to the lift1 generated by the flapping of its wings. For wasps, this mechanism is called the clap-and-fling phenomenon (Sane, 2003). It works in two stages as shown in Figure 1. In this figure, the dot represents the leading edge of the wing, the front facing end, and the line following it represents the trailing edge, the back part of the wing (refer to Figure 2 for a visual representation). The first stage is demonstrated in Figure 1 from the letters A to C. This mechanism is called the clap of the wings. The wasp initially brings the two leading edges together and then rotates its trailing edges, pushing down the air in between. This creates a compact, single surface which ultimately generates lift. The horizontal forces generated by the vortexes of air created on each side of the wing cancel out and only the lift remains (Sane, 2003). The clap mechanism also aids the wasp by allowing it to almost nullify the Wagner effect2 to achieve lift at a faster pace. This is a necessary task for such an organism to conserve energy (Sane, 2003). When the clap stage ends, the fling stage, shown by the letters D to F, begins. The wasp pronates the leading edges whilst keeping the trailing edges stable and pushes down with its wings during the pronation. This creates an imbalance of air where the pressure on top of the wing is lower than the pressure at the bottom of the wing. To balance this difference in pressure, air flows to the lower pressure zone rapidly which generates vortexes of air above the wings (Sane, 2003). This ultimately leads to a lift being generated. The movement of air by the forward momentum of the wasp also generates a drag force on the wings which affects the resulting force of the fling mechanism. The lift force as well as the drag force generated during the fling stage are represented in Figure 3 (Sane, 2003).  

Fig. 1 Diagram of the clap-and-fling phenomenon of the wings of a wasp illustrated by the leading edge (the dot) and trailing edge (the line following the dot) representation shown in figure 2. This shows the different steps of the path that the wing follows during the flight of the wasp. The clap is shown via the letters A to C and the fling is shown via the letters D to F (Sane, 2003). 

Fig. 2 Drawing of an insect. The leading edge and the trailing edge are represented by a dot and a line which follows. This shows how the wing is represented in drawings (Sane, 2003). 

Fig. 3 Diagram of airflow around wings. (A) The movement of wind around of a blunt wing and the forces acting of the wing. (B) The movement of wing around of a thin airfoil, the forces acting on the wing, and the resulting force on the thin airfoil (Sane, 2003). 

The flapping of a wasp’s wings, combined with the use of wake capture3, allow the wasp to create enough lift to carry prey equivalent to their body weight during flight (Dudley, 2018). To calculate the power outputted by the muscles, the formula: 

(1)   \[P^*_{\text{muscle}} = \frac{\sigma \epsilon n}{\rho} \]

P* represents the power output per unit of mass of muscle, σ represents the amount of force generated per unit cross-sectional area of muscle, ϵ represents the change in the length of the muscle during contraction, n being the frequency at which muscles contract per second (wingbeat frequency), and ρ being the muscle density (Dudley, 2018). Since wasps are only able to carry the equivalent of their body weight, they will tend to hunt for prey of a similar body weight to ease the transport back to the nest (Hickey et al., 2022). However, species such as spider wasps can hunt larger and heavier prey. In such cases, instead of carrying the prey carcass in flight, they often drag it back to their nests, since a single wasp does not have the power necessary to generate enough lift for flight with significantly heavier loads (Hefler et al., 2021). Some wasps, such as yellowjackets, reduce the mass of their prey prior to their flight by dismembering their body parts. This allows them to reduce energetic costs associated with bringing back food to their nest (Dudley, 2018). 

Stability during flight for small insects such as wasps is crucial because they are more prone to getting swayed off course by air currents or turbulence. For that reason, wasps can maintain stability during flight in various ways, some of them active via changes in wing and body orientation, and some passive via drag forces and body (Dudley, 2018). Three types of deviations, illustrated in Figure 4, can alter the course of any object in flight. These are pitch, roll, and yaw, each of which is responsible for the rotation of a flying object in a three-dimensional plane (Dudley, 2018). Wasps respond to these rotating forces by analyzing visual stimuli and by compensating with an increase in wingbeat frequency (Dudley, 2018). 

Fig. 4 Diagram of the different torques acting on the body of a wasp during flight. The present torques4 are pitch, roll and yaw (Dudley, 2018). 

Effect of environmental factors on flight 

The effects of environmental factors including the direction and speed of air currents, atmospheric temperature, humidity, and air density on lightweight such as wasps are immense (Pringle, 2003). 

The direction and speed of air currents affect the wasp’s aerodynamic efficiency, depending on whether it flies with or against the airflow. In the case where the wasp moves alongside of the air current, less energy is needed for thrust (a horizontal force) since the wind reduces the drag experienced on the body. Conversely, flying against air currents increases the drag on the body of a wasp. To compensate, the wasp exerts more energy to flap its wings at a greater intensity. By doing so, more thrust is generated to combat the increase in drag forces. This is also the case with updrafts and downdrafts. Updrafts aid wasps to gain altitude in their flight because of the upward drag forces applied on the body (Pringle, 2003). Thus, the wasp does not need to generate as much lift to gain altitude or to stay afloat. In contrast, downdrafts cause a downward drag on the body of the wasp. As such, a wasp must spend a higher quantity of energy to generate enough lift to gain altitude or to stay afloat. Wind turbulence also affects the energy consumption of wasps. In turbulent winds, wasps require a greater amount of force to stabilize itself against the inconsistent patterns of wind (Pringle, 2003).  

Moreover, atmospheric temperature affects the flight of wasps because most wasps are ectothermic organisms. This means that their body temperature is regulated by the atmospheric temperature (Käfer et al., 2012). In lower temperatures, the muscle activity of wasps decreases, which leads to a reduction in the maximum amount of force generated by the organism. To avoid entering a state of torpor at low temperatures, wasps must invest extra energy in keeping their internal temperature above 2.9°C (Taylor, 1963). However, higher temperatures can be lethal for most wasps because symptoms such as overheating deplete energy more quickly, and heat buildup can lead to death. An optimal temperature for most wasps is around 15°C to 25°C since the metabolic energy produced by the wasp is around equal to the energy to generate lift and thrust without there being too much heat buildup (Käfer et al., 2012). It is also between these temperatures that a wasp can achieve its maximum output of force, since the frequency at which it can bat its wings is the highest (Taylor, 1963). This is also the phenomenon that explains the honeybee defense mechanism against wasps. Whenever a wasp approaches a honeybee hive, it is quickly surrounded by numerous honeybees that bat their wings rapidly to raise their internal body temperatures (Käfer et al., 2012). By doing so, they manage to bring the internal body temperature of the wasp above the wasp’s maximal heat resistance which leads to its death (Käfer et al., 2012). This interaction happens because the maximal temperature that a honeybee can withstand is around 49°C compared to the wasp’s 42.4°C (Hefler et al., 2021). 

Fig. 5 Formation of a hot defensive ball by honeybees around of a wasp. (A) A wire is attached to a wasp. (B) Bees start forming a ball around the wasp and increasing their body temperatures. (C) The bee ball is placed in a glass beaker. (D) 60 minutes after the bee ball forms, the wasp is dead (Ugajin et al., 2012) 

In addition, humidity and air density play a crucial role in the flight of wasps because they dictate the behavior of the air for smaller scale organisms such as wasps (Tang et al., 2012). An accurate representation of this behaviour is the Reynolds number which is calculated from the formula:  

(2)   \[Re = \frac{\rho v L}{\mu} \]

The variable ρ represents the fluid density, v represents the velocity of the fluid, L represents the characteristic length of the object and μ represents the dynamic of the fluid (Tang et al., 2012). A low Reynolds number indicates smooth flow of fluid, whilst a high Reynold number indicates turbulent flow of fluid (Tang et al., 2012). For wasps, the Reynold numbers vary from 100 to 1000. As such, wasps often find themselves either in smooth conditions with stable airflow and vortexes that dissipate quickly, or in more turbulent conditions with unstable airflows and stronger vortexes. Stronger vortexes allow wasps to generate more lift due to enhanced wake-capturing (Käfer et al., 2012). This relates to humidity levels in the air, since as the air becomes more humid, air density decreases (the molar mass of water vapor is less than the molar mass of air) and air viscosity increases (Volynchik et al., 2007). This directly reduces the Raynolds number in the ambient air. As a result, wake-capturing to generate lift for smaller organisms such as wasps is more difficult and energy intensive (Tang et al., 2012). 

Wing and body shape 

The wings are one of the greatest assets for a wasp because it allows them to maneuver seamlessly through the air and propel themselves at great speeds (Perrard, 2020). These different qualities are found within all wasp species, with some exceptions, but the of the different aerodynamic capacities from one species to another varies based on factors such as the shape of the wing and the shape of the body (Perrard, 2020).  

Pointed wings have evolved to decrease the drag force created during flight and enable rapid direction changes in flight (Perrard, 2020). A correlation between pointed wings and elongated bodies and longer petioles (waists) has also been determined (Perrard, 2020). A longer body creates more drag for an organism which increases stability during flight. As the larger body interacts more with the surrounding air, there is more resistance to non-intended changes in direction, so the wasp can experience a higher quantity of control during its maneuvers (Perrard, 2020).  

Rounded wings have an enhanced ability to generate lift and thrust at the expense of creating more drag on the wing itself (Perrard, 2020). As such, this allows the wasp to fly at greater speeds for longer distances because the forces generated by the wings (3 x 10-3 N) are largely superior to the drag (4.41 x 10-5 N). A correlation between round wings and shorter bodies and petioles has also been observed (Perrard, 2020). A shorter body is designed to be streamlined which minimizes the drag forces experienced by the wasp at high speeds. However, shorter bodies reduce maneuverability and causes the wasp to be more vulnerable to turbulence during flight (Perrard, 2020). 

For predatory wasps that require high speeds to catch up with their prey, a shorter body and rounded wings are preferable. For wasps that pollinate and forage for nectar, long bodies and pointed wings are better suited since it allows for better maneuverability (Perrard, 2020). Different evolutional needs modify the body structure of different species as seen in Figure 6. 

Fig. 6 Graph of wing and body shapes depending on what optimum is required in a certain environment where the y axis shows the wing shape, the x axis shows the body shape, and each dot depicts a certain wasp. (A) No specific optimum in the environment. (B) Optimum requires a balance between speed and maneuverability. (C) Two optima are present with either high speed or high maneuverability being favored. (D) Three optima are present (Perrard, 2020). 

The Wasp’s Body 

Vision mechanisms of the wasp 

Anatomy of the compound eye 

Evolution has provided wasps with many adaptations to survive as an organism and as a superorganism. For instance, its sensory abilities contribute greatly to essential activities, namely sight, which is an important sense in a wasp’s life. 

Fig. 7 Compound eye of the cuckoo wasp (Eaton, 2021) 

While wasps do have sensory organs to perceive and interpret visual stimuli, their eyes are drastically different from camera eyes. They possess what is called a compound eye, which is quite common among arthropods, such as insects or crustaceans (Nilsson, 1989). While camera eyes possess one lens converging light rays to a receptor, compound eyes are composed thousands of such systems, called ommatidium. These ommatidia are composed of a lens and a photoreceptor, the rhabdom (Horridge, 1978). While all compound eyes adopt this structure, there are two types of compound eyes which have slightly different modes of action to adapt to different environments. The first type is called the apposition eye. In an apposition eye, the photons first pass through the lens, called the cornea, and are converged through the crystalline cone. This cone is surrounded by pigment cells that acts as an opaque surface, thus preventing light rays from spilling out to other ommatidia. The crystalline cone also acts as a lens, converging further and channeling the photons through the photoreceptor part of the ommatidia, the rhabdom. The rhabdom is a long tube composed of several individual photoreceptor cells, called rhabdomeres. These cells are covered in microvilli, which receive photons and transmit light information as electric signals through axons along the rhabdom. The axon bundles of each individual ommatidium are then merged into an optic fiber, transmitting the visual information to the brain to be interpreted (Ignatova, 2018). An apposition eye is composed of about 1000 of these ommatidia (Fischer, 2010). This apposition eye is more common in diurnal arthropods species and is the type of compound eye possessed by wasps (Nilsson, 1989). 

Fig. 8 Anatomy of the apposition eye. (Ignatova, 2018) 

Inversely, nocturnal arthropods’ compound eyes are slightly different, as they are adapted to nighttime and can deliver more photons to the photoreceptor cells. In supposition eyes, after passing through the cornea, the photons are not confined by pigment cells, but are rather converged by the lens into the “clear zone.” In the clear zone, the pigment cells are transparent and do not confine photons. These photons can therefore spill to other ommatidia. This does not however cause blurry vision, as the ommatidia are positioned such that the cornea’s aperture diffracts the light precisely in a way that will converge the light from many ommatidia into one photoreceptor cell. Therefore, each photoreceptor cell captures more photons, which allows the superposition eye to be better adapted to nocturnal vision. During the day, if this system is unchanged, vision would be in low resolution, as many ommatidia converge to only one photoreceptor. To prevent that, pigment cells migrate from the photoreceptor’s region to the crystalline cone to act similarly to pigment cells in apposition eyes (Land, 1999). 

Fig. 9 Comparison of optical activity of apposition and superposition compound eyes. (Schroer, 2017) 

Resolution of the apposition eye 

To describe the physical and optical properties of the apposition eye, it is necessary to first describe certain physical values in the eye. Firstly, the inter-ommatidial angle 𝛥𝜙 corresponds to the angle between two consecutive ommatidia and can be calculated by the small angle approximation with: 

(3)   \[\Delta \phi = \frac{A}{R} \]

R is the radius of curvature of the eye, A is the diameter of the aperture of the cornea of an ommatidium, and d is the diameter of the rhabdom (Land, 1999). Δρ is the rhabdom acceptance angle, which is defined as the angular width of the circle on the rhabdom in which the light intensity is at 50%. This circle is called the “blur circle” (Horridge, 1978). The linear equivalent is Δα, which is the diameter of the blur circle (Horridge, 1978). 

Fig. 10 Physical and optical properties of the apposition compound eye (Land, 1999). 

Eye resolution is limited by two crucial factors. One is spatial frequency, which is the finest detail the eye can resolve due to the separation of each ommatidia. As it takes two ommatidia to discern a cycle of a grating, the spatial frequency corresponds to the reciprocal of the spatial period (Land, 1999), namely: 

(4)   \[v_S = \frac{1}{2\Delta\phi} = \frac{R}{2A} \]

Diffraction entails another limit on the eye resolution. Indeed, some frequencies will not be captured by the rhabdom because of the diffraction figure. The highest spatial frequency that will be captured is then called “cut-off frequency” and corresponds to: 

(5)   \[v_{CO} = \frac{A}{\lambda} \]

where λ is the wavelength of the light (Land, 1999). Empirical data suggests that v_S and v_{CO} match (Land, 1999), and we can then combine the two equations to obtain: 

(6)   \[v_s^2 = \frac{R}{2\lambda} \iff R = 2 \lambda v_s^2 \]

This result shows that the radius of a compound eye is proportional to the square of its resolution. Using a value of Δ𝜙=1°, which is a typical value for wasp compound eyes (Land, 1999), and light at a 500 nm wavelength, we get a radius of 0.821 mm, which corresponds to the size of an apposition eye (Land, 1999). However, this resolution is drastically inferior to that of a camera eye. To demonstrate that, the human inter-receptor angle is Δ𝜙 = 0.5′ ≈ 0.0083° (Land, 1999). Using the same wavelength, the calculation gives an eye radius of 11.9 m. Therefore, for a wasp to have similar resolution to the eye of a human, its eye would have to be about 14500 times bigger! It is then clear that resolution is not the apposition eye’s strength, but it can compensate in other key features. 

Ommatidia density and inter-ommatidial angle is not constant throughout the apposition eye. Indeed, evolution has led to many adaptations in the eye’s structure to optimize its activity, and some regions of the eye have a higher ommatidia density than others. These regions are called “acute zones” (Land, 1999) and are created by many factors. Firstly, as a wasp flies forward, objects in lateral position relative to the wasp appear to be moving backwards. Inversely, objects in front of the wasp, there is a point where objects do not move at all. Furthermore, closer objects appear to be moving faster than farther objects. This can be summed up by the equation: 

(7)   \[\frac{d\alpha}{dt} = \frac{v \cdot \sin a}{x} \]

where \alpha is the angle between the object and the wasp’s trajectory, \frac{d\alpha}{dt} is then the angular speed of the object relative to the wasp, v is the wasp’s velocity and x is the distance between the object and the wasp. It is then clear that objects forming a 90° angle with the wasp and close to it will appear to be moving very fast, which would cause blurring in the image. The maximal resolution of the apposition eye is therefore useless for lateral regions, as this resolution is not usable because of this physical limitation, and the inter-ommatidial angle will vary consequently. Indeed, considering an angle of 90°, a speed of 2 m/s which is usual for wasps (Land, 1999), and a distance of 0.5 m, we can calculate an angular speed of 229°/s. A typical reaction time for insects is around 10 ms (Land, 1999). Therefore, during one interval of response time, the object will have moved an additional 2.3° and it is practically useless for the wasp to possess an inter-ommatidial angle of less than 2.3° for that region of the eye. Empirically, this reasoning is indeed verified, as most insects’ inter-ommatidial angle increases by about one degree between the front of the eye and the lateral section (Land, 1999). 

Secondly, another inter-ommatidial angle gradient can be observed in the apposition eye of the wasp. Indeed, the inter-ommatidial angle increases vertically from the center of the eye to its poles (Land, 1999). This is due to the higher information density around the horizon, and evolutionary patterns responded accordingly by creating this gradient. Acute zones are useful for wasps as a superorganism in many ways. Indeed, they are favorable for localizing and catching prey as well as mating purposes (Land, 1999) and are a prime example of evolution giving form to superorganisms. 

Adhesive capacities of the wasp’s legs 

Another important aspect of the wasp is the capacity of a wasp to move and resist. These can be useful against predators or for catching prey, since it allows them to move quickly and efficiently to flee danger or attack prey. Wasps have the astounding capacity to stick and walk on almost any surface, regardless of its orientation. Indeed, they have remarkable adhesive properties to smooth surfaces. For instance, experiments showed that some species can withstand detachment forces equivalent to more than 100 times their body weight (Federle, 2002), yet these insects are still able to run freely on the same surface. This surprising dichotomy reveals a complex adhesive mechanism in insect legs.  

Fig. 11 An example of a wasp adhering to a smooth surface: a leaf (Vetter, 2002). 

Wasps are equipped with tarsal claws at the exterior edge of their legs. In between these claws, there is the arolium, which is a lobe-shaped structure contributing to adhesive capacities by Van der Waals forces as well as surface tension (Walker, 1993). 

Fig. 12 Anatomy of a wasp’s tarsus (Infectious learning). 

The tarsus of the insect is composed of a single muscle, controlling these two tarsal claws: the claw flexor muscle. Hence, attachment to a smooth surface is initiated by this muscle’s contraction. The claws are then clenched into the surface, and the arolium is attached in two motions. It is first folded down to the surface, then expanded laterally (Federle, 2002). The arolium is covered with adhesive setae, which is a stiff hair-like structure carpeted on the arolium’s surface. Since Van der Waals interactions are relatively weak and act over short distances, surface contact is an important factor in determining adhesion forces. The presence of setae also reduces the distance between the wasp’s point of contact and the surface, thus intensifying Van der Waals forces (Walker, 1993). As for detachment, since the claw flexor muscle has no antagonist muscle, the claws and the arolium are retracted by elastic recoil, similarly to a spring (Federle, 2002). 

The attachment-detachment process described above is called “active extension”, as it is mediated by an active process: the contraction of the claw flexor muscle. Interestingly, wasps also have a passive extension mechanism, relying on purely passive mechanical processes. Indeed, this process does not require any neuronal activity and occurs automatically and instantly to prevent disruptions caused by external factors. For instance, this allows wasps to stay on the surface even in the presence of a gust of wind. Surprisingly, since this reflex does not rely on any neuronal activity, it can even occur when the insect is dead! (Federle, 2002) 

In essence, this stunning capacity to cling to smooth surfaces grants wasps many advantages as an organism. Indeed, this is an effective defense mechanism, as it allows quick, sharp, and all-around displacements, which is a very useful asset against natural or animal dangers. Once again, evolution allows species to develop various mechanisms to survive and advance as a superorganism. 

Defense Mechanisms 

Mandibles 

To accomplish many common tasks such as chewing prey or building a nest, social wasps use their strong and uniquely shaped mandibles. The shape and structure of mandibles varies depending on the needs and functions of different species. In most insects, the powerful biting force comes from the development of mandibles with two fixed joints and restricted movement due to the single axis of rotation, as well as an anterior articulation to the head capsule. (Van de Kamp et al., 2022). Interestingly, some parasitoid wasps have evolved to gain more flexibility in their mandibles. In social wasps, the mandibles are short bilaterally symmetric structures that are wide basally and flattened distally, with teeth at the end of each mandible. The mandibles close with the help of strong adductor muscles, moving just below the head capsule in a horizontal plane. As the mandibles close, one slides under the other and an inward movement allows for one mandible to lay over the other in a resting position. During this movement, the mandibles can perform various mechanical functions, as seen in Figure 13:  their tips can oppose or cross at the middle, the apical teeth on one mandible can interact with the denticles on the other to cut, and the front edge of the mandible can cut against the bottom edge of the wasp’s clypeus. The anatomical features mentioned are shown in Figure 14.  

Fig. 13 Scanning electron micrograph of (A) Ventral view on the head showing the interaction between both mandibles (80µm) (B) Ventral view of right mandible with magnification of the scratches on the tip (20µm) (C) Magnification of scratches on lateral surface of left mandible (4µm) (D) Medial view of right mandible showing sharp cutting edge of the mandible (20µm) (Adapted from Krings et al., 2024) 

Fig. 14 Wasp feeding apparatus, where the clypeus is seen right above the mandibles (Vespa-Bicolor, 2006)  

Moreover, there is a significant correlation between nesting materials used by wasps and the structure of their mandibles. The most common nesting materials are long plant fibers obtained from hard woods and short plant fibers coming from soft wood, amongst mud, clay and plant hairs. Given the complex behavior of chewing and handling nesting materials, “wear and tear” happens due to constant manipulation of wood fibers. To increase the hardness and durability of the mandibles, the apical teeth of social wasps have evolved to incorporate metals such as Manganese and Zinc in them as seen in Figure 15 (Sarmiento, 2004). In the same study, Sarmiento observed that species using long fibers typically have longer apical teeth on their shorter, slightly curved mandibles, whereas those using shorter fibers have less developed apical teeth, likely due to their preference for softer wood fibers for nesting. In a different study by Kiran Vati K. and Bhasker Shenoy K., they showed that for social wasps that use plant fibers for nesting such as the Vespa tropica or Ropalidia marginata, the specific structure of the mandible (short and wide) allows for better fiber management and prey chewing with a reduced energy-loss. This is contrary to the statement of Sarmiento which suggests that shorter mandibles are less efficient for chewing prey, which increases the energy cost of food processing. More research must be done to identify the exact correlation between the diet of the wasp and its nesting behavior on the structure, size and shape of its mandibles. Due to the huge amount of wasp species, from social to solitary to parasitoid wasps, there is ample room for more research and experimentation. It has already been stated that different species of social wasps have a different number of apical teeth too! There is still much to learn about this topic. 

Fig. 15 Results from EDX analysis, given in atomic %. Elemental content of the tip, the lateral and medial surfaces of the mandibles. (Krings et al., 2024) 

Ovipositor  

All wasps possess an -laying organ called an ovipositor. It is a tube-like structure attached to the abdomen of a wasp, either concealed within the abdomen or protruding from its tip. Parasitic wasps use their ovipositor to insert their eggs on or in a host plant or animal. Certain parasitic species need their ovipositor to reach deep inside their host. Some have even evolved to have them reach up to 12 times their body length! To dive into the mechanics of the ovipositor, some terms need to be defined. The ovipositor is composed of two pairs of elongated appendages, the gonapophyses or ovipositor valves, which form the channel down which the egg travels. The specific arrangement of the valves allows for extra flexibility in movement. Protecting the ovipositor are a pair of remarkably strong and thick sheaths called the gonoplac, that are essentially two lateral concave plates that form a protective layer over the ovipositor. (Eaton, 2021) 

To enter her host, the wasp works the gonaphysis valves in a sliding manner, moving them reciprocally during insertion. In this context, “reciprocally” means the repetitive linear motion of the valves sliding back and forth.  This “push and pull” mechanism allows the ovipositor to penetrate hard surfaces with minimal energy loss. Moreover, the tips of some gonaphysis valves are toothed (or rather serrated). With the specific design shown in Figure 16, it is made easier for them to penetrate plant tissue or a host animal. In some species like chalcidoid wasps, the apex of the ovipositor shaft (terebra) is heavily hardened with metal atoms such as calcium, manganese and zinc, to enable the piercing of hard tissue and increase the durability of the ovipositor. The presence of heavy metals within the sclerotized matrices of the ovipositor improves the efficiency of penetration in hard substrates and enables wear resistance. These articulate designs presumably reduce the mechanical stress during probing and limit the risk of damage by distributing the required pushing force along the terebra. (Eggs et al., 2023) 

Fig.16 (a) Scanning electron micrograph of a wasp ovipositor showing serrations. (b) Ovipositor valves protected by sheath layers. (Adapted from Gundiah, 2020) 

Mechanisms of movement 

From a mechanical perspective, it is quite difficult to drill into a solid substrate with a very thin probe, because it can easily bend and break. How do parasitic wasps do this when inserting their thin ovipositor into the hard tissue of their host? Wasps can steer and curve their ovipositors in any direction relative to their body orientation which allows them to probe with a minimal net pushing force. Contrary to soft substrates, stiff substrates require reciprocal motion of the valves to be penetrated. Unfortunately, this important mechanism is not completely understood and very little is known about the magnitude of forces generated during probing. Perhaps it is because multiple species of wasps are very tiny or simply because probing was only studied when the ovipositor was in a resting position. Nevertheless, there is still pertinent information about the movement of the ovipositor and many hypotheses regarding the benefits of such movement. Although the studies pertain to parasitic wasps, it can be thought that social wasps work in a similar fashion with less advanced mechanisms. 

The two ovipositor valves mentioned previously each consist of one ventral valvulae called the ‘first valvulae’ and a dorsal one called the ‘second valvulae’, which were merged longitudinally through evolution processes to form the olistheter system. This allows the movement of the valves without the possibility of separation. Interlocked together, they oscillate back and forth without any rotary motion needed. This phenomenon is called the olistheter mechanism, which is the longitudinal sliding motion of the interlocked valves, shown in Figure 17. As a result, there is a near net zero force parallel to the ovipositor, meaning that the wasp does not need to exert significant effort when pushing into its host. The advantages of such a system include many, such as the increased stability and control during penetration, the reduced , and the improved coordination of the valve movements. Additionally, during the initial insertion of the ovipositor into the host, the interlocking mechanism described above pushes only certain valvulae into the substrate while simultaneously pulling on other ones that are already fixed into the substrate in a reciprocal manner. This specific “push and pull” motion increases the ovipositor’s ability to withstand bending under the application of an external force, in this case, penetration. So far, we have seen how the physical properties of the wasp ovipositor can allow for extra flexibility and bending, but how can they steer this little organ? Well, we don’t know for sure! It has been hypothesized that the olistheter mechanism plays a significant role in steering the ovipositor. The idea initially came from the analysis of the wasp D. longicaudata. Researchers noticed that whenever the wasp protracted its first valvula, the ovipositor assumed a curved trajectory, and when the second valvula was protracted, straight insertions were observed. It is incredible how the kinematics of the valves dictates the accuracy of the “egg-laying mechanism”, and it shows how important it is in the successful reproduction of wasps. (Van Meer et al, 2020) 

Fig. 17 Sliding motion of the ovipositor valves during the olistheter mechanism (Alkalla et al, 2019) 

Stinger 

When we think about wasps, we tend to associate them with “danger” due to their powerful stinger. It is less commonly known that only females of certain species have stingers! In this section, we will investigate why some females have this weapon while males and other females don’t. First, it is crucial to state that the stinger is a weaponized ovipositor, the egg-laying organ of wasps. It evolved as such to improve the defensive and predatorial skills of different species of wasps. Of course, not all species have stingers since not all of them need stingers. Considering that only female wasps have an ovipositor, then only they can have stingers. Although males don’t sting, some of them have developed a ‘fake’ stinger to shield them from potential danger as it acts as a warning to predators. There ‘fake’ stingers pose no real harm to predators as they are non-venomous. A stinger supports wasps in more than one way. Not only does it act as a defense mechanism, but it is also used to incapacitate prey using its venom. That is actually its primary function; to induce the temporary or permanent paralysis of its prey so it is easier to carry and resists less.  As a consequence of evolution, the stinger is very similar in structure to the ovipositor, except it is sharp with no ‘teeth’ at its tip and it lacks both protective sheaths that ovipositors have. Inside the stinger, there is a channel where the venom flows through and reaches its target. Wasps have an incredible ability to manipulate their stinger and direct it wherever it is needed to attack their prey. That is due to the flexibility in their abdomen and their miniature “wasp-waist”, which allows for a remarkable range of motion! (Eaton, 2021) 

Fig. 18 Stinger in female wasp (Rescue, Smarter Pest Control) 

Conclusion

The wasp acts as a source of inspiration in evolutionary engineering where design principles are deeply rooted in biomechanical and physical phenomenology. They have evolved clever design solutions to improve their function and survival. These include wake capture during wing flapping to increase lift, elastic recoil that retracts their claws and arolium for gripping smooth surfaces, and fake stingers in males for predator protection. An example is the clap-and-fling flight mechanism, which illustrates how exquisitely balanced energy efficiency and aerodynamic lift together enable the wasps to carry loads equal to their body weight while remaining stable in turbulent flow conditions. This is important for their survival and reproduction as they can carry prey to their nests and feed the larvae. The body structure of wings was also optimized for shape and the material to optimize its speed and maneuverability. Compound eyes are uniquely adapted to manifest an elaborated interaction between form and function. Indeed, by their increased visual resolution due to a gradient in ommatidia density, they ensure their survival and efficiency in predation. The complex structure of their legs grants them an impressive adhesive capacity. Indeed, the adhesive setae covering their legs and the arolium allow them to adhere and move efficiently on almost any surface. The stinger, ovipositor and mandibles showcase the evolutionary pressures that have sculpted the wasp’s anatomy for a variety of tasks such as defense, incapacitating prey and nest building. Wasps epitomize the ideal balance of structure and function, as even minute details of flight dynamics and mechanisms of sensory capabilities have been elaborated for the survival of wasps in various ecological zones.  

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