In Focus

Mimicry

In evolutionary biology, mimicry is an evolved resemblance between an organism or another organism or an inanimate object. Before we dwell deeper into the different mimicry concepts, let’s get some fundamental terms correct. When we refer to the word “mimic”, we mean the organism that has a resemblance to something else, while the “model” refers to the organism the mimic is trying to resemble or pretending to be.  

Often, mimicry functions to protect a species from predators, making it an anti-predator adaptation. This is usually done by the mimic imitating another venomous/ poisonous or aggressive model to avoid being attacked and eaten, or by avoiding being detected in the case of mimesis, where the “mimic” imitates/ masquerades as inanimate object or surroundings as a means of camouflage. This can include an animal mimicking a plant part as well, so as long it mimics a non-animal model.

1. Mimesis (Mimicry non-animal model/ “inanimate” objects)

Mimesis is common in prey animals especially insects, where the prey organism mimics a twig, live or dead leaves, moss and lichen. Below are some examples of Orthopterans that look like dead (Figs 1-4) or living (Fig 5) leaves, crustose (Fig 6) or foliose (Fig 7) lichen and leafy liverwort epiphylls (Figs 8 & 9).

Members of the Order Phasmatodea (Stick and Leaf Insects) have taken mimesis to the next level, where most of the species either resemble twigs/ branches (mostly in the tribe Lonchodini) (Figs 10-12), moss (Figs 13 & 14) or leaves (Fig 15).

Phasmids that are not cryptically camouflage, usually deter predators by being brightly colored advertising toxicity through bright warning colors (Fig 16) or by being able to emit foul odours (Fig 17) or in the case of Megacrania batesii (Fig 18), it emits peppermint like smell, but predators still avoid it because the chemical irritates the eyes or taste bad.

In Lepidoptera, mimesis is more common in moths than butterflies, but some butterflies do mimic dead leaves (Fig 19 & 20). Moths take mimesis to a new level, some look like leaves Many moth species look like dead leaves (Fig 21), living leaves with lichen and other epiphylls growing on them (Fig 22), tree bark with lichen growth (Fig 23), some even take on the form of bird dropping splatter with attending flies (Fig 24), dead twig segments (Fig 25), flower buds (Fig 26) and even flash hidden eyes when threatened to scare off predators (Fig 27).

Mimesis is also employed by some predators and parasites to lure their prey. For example, flower mantis (Tribe Hymenopodini) mimics flower such as orchids and other flowers (Figs 28 & 29).

Mantis species in the family Deroplatyidae adopt ambush predation by remaining undetected, mimicking dead leaves (Figs 30-32). Other mantis species also mimic living leaves like Choeradodis rhomboidea (Fig 33), Rhombodera valida (Fig 34) and Epsomantis tortricoides (Fig 35), while members of the family Toxoderidae (Dragon Mantises), have species resembling dead branches and twigs) (Figs 36 & 37).

Other like mantis species like Theopompa borneana (Bornean Bark Mantis) (Fig 38) have disruptive coloration that blend with the bark or are able to flatten out onto leaves like Epsomantis tortricoides (Fig 39).

Reptiles and amphibians also employ mimesis to avoid predation and also to ambush their prey. The Spiny Hill Terrapin (Heosemys spinosa) (Fig 40) have young that resemble dead leaves. While the adults retain the general color scheme into adulthood, the texture and shape of the shells are less convincing when they are adults. Other snakes, lizards and frogs employ camouflage to not only avoid predation, but also as a means to ambush their prey. While many snakes are masters of camouflage and employ disruptive coloration to avoid detection, Southeast Asian Whipsnakes (Fig 41) have also developed very thin elongated bodies that look like vines, while the Madagascar Leaf-nose Snake (Fig 42) takes this a step further and not only with their bodies looking like vines but also have appendages at their nostril area, which make them look very atypical to most snakes.

The Malayan Horned Frog (Megophrys nasuta) (Fig 43) disguise themselves as leaves on the forest floor, and wait for unsuspecting prey to wander past. Theloderma​ albopunctatum lie motionlesss on leaves with their bodies flattened out when resting, making themselves look like a pile a bird poor. Some species of geckos like the genus Uroplatus have amazing and varied camouflage allowing look like dead leaves (Fig 44), fissured tree bark (Fig. 45), and lichen (Figs 46 & 47)

Birds have also adopted mimetic camouflage to escape predators. Some species like Black-naped Terns have chicks that are similar colour to their background (Fig 48) to avoid detection by predators, especially birds of prey. In other species, even the adult birds are cryptically coloured to help in predator avoidance (Figs 49-53). In the bird order Caprimulgiformes, many species not only so cryptically coloured and patterned, but also adopt sleeping postures that allow them to hide in plain side, mimicking dead tree stumps or branches (Figs 51 & 52). Owls also adopt cryptic coloration to allow them to sleep during the day and avoid being predated on by other diurnal birds of prey (Fig 53).

2. Defensive mimicry

Defensive mimicry takes place when organisms avoid harmful encounters by deceiving enemies into treating them as another animal “model”.

The first three types of defensive mimicry involve the mimic being protected by warning coloration of their models:

• Batesian mimicry
• Müllerian mimicry
• Mertensian mimicry

Batesian mimicry, where a harmless mimic poses as harmful, but does not have the attribute that makes it unprofitable/ unpalatability to predators. In other words, a Batesian mimic is a sheep in wolf’s clothing. Some such examples are cuckoos (Figs 54 & 55) that mimic birds of prey with similar plumage such as goshawks (Fig 56), sparrowhawks, Shikra, while hoverflies (Figs 57-59) and some longhorn beetles (Fig 60), mimic wasps (Fig 61) and bees (Fig 62).

Müllerian mimicry describes a situation where two or more species have similar warning or aposematic signals and both have genuine anti-predation attributes such as being venomous or highly aggressive. Firstly, both the mimic and the model benefit from the interaction, which could thus be classified as mutualism.

The signal receiver also benefits from this system, despite being deceived about the species identity, they learn to associate and generalize the pattern to potentially harmful encounters. Some clear cut examples are wasps (Fig 61) and bees (Fig 62), which share the same general striped abdominal pattern, which would-be predators learn to associate with being stung.  

Mertensian mimicry, where a deadly mimic resembles a less harmful but lesson-teaching model. This scenario is unusual, as it is usually as the model is usually the more harmful. But if a predator dies on its first encounter with a deadly model, it has no occasion to learn to recognize the model’s warning signals. There would then be no advantage for an extremely deadly model in being aposematic, since any predator that attacked it would likely be killed before it learn a lesson and a better tactic would be to avoid being detects through camouflaged to avoid attacks altogether.

In the case of the Striped Kukri Snake (Oligodon octolineatus) (Fig 63) and the Malayan Banded Coral Snake (Calliophis intestinalis) (Figs 64 & 65), the exact defensive mimicry model is not as clear cut. The reason for this is, with regards to both species, the predator’s learnt lesson may be highly subjective.

While coral snakes are assumed to be highly venomous, but most bites of this species have proven to be non-fatal since, this species are usually not aggressive and flee rather than to attack. They also have very small mouths, and combine with being rear-fanged, would result in a “dry” bite or a poorly envenomated bite. And as such most encounters with this assumed-highly venomous snake usually results in no lesson learnt by the predator. On the other hand, while the Striped Kukri Snake is non-venomous, it is extremely aggressive and have extremely sharp serrated kukri shaped teeth, which can inflict a non-venomous but nasty and painful bite, which is lesson well learnt.

To complicate things, the Malayan Banded Coral Snake also has two color forms, one with a more striking aposematic look (Fig 65), while the other form is less striking (Fig 64), but looks very similar to the Striped Kukri Snake (Fig 63). As such it is unclear which is the mimic and which, is the model, as lesson learnt varies with the situation.

3. Aggressive mimicry

 Aggressive mimicry is found in predators or parasites that share some of the characteristics of a harmless species, allowing them to avoid detection by their prey or host and can be compared with wolf in sheep’s clothing. The mimic may resemble the prey or hos, or another organism that is either neutral or beneficial to the signal receiver. In this class of mimicry, the model may be affected negatively, positively or not at all. Just as parasites can be treated as a form of predator, host-parasite mimicry is treated here as a subclass of aggressive mimicry.

Ant mimicking spiders are a good example of aggressive mimicry, with many spider families having ant-mimicking species. These spiders not only resemble ants in appearance, but also behave like the ants they mimic. This mimicry extends beyond appearance and behaviour, but also chemical mimicry, allowing the spiders to come in close proximity to the ants and interact with them without their true identity being discovered. This mimicry allows them to spend time not only in the ant territory (Fig 66), but right amongst the colony without becoming prey for the ants (Fig 67). This allows them to effectively predate the ants (Fig 67), without becoming the ants meal.

Besides spiders, lepidopterids are an unlikely aggressive mimic. Caterpillars of the family Lycaenidae have a varied diet and apart from plant matter, the larvae of some species feed on aphids, scale insects, and ant larvae. 75% of Lycaenids are associated with ants, and can be mutualistic, parasitic, or predatory depending on the species. Some lycaenids even exploit their association with ants by inducing ants to feed them by regurgitation. In other species, the larvae are protected by ants while they feed on the host plant, and in return the ants receive sugar-rich honeydew.  In some species, only the first few instars are spent on the host plant, and the remainder of the larval lifespan is spent as a predator within the ant nest. The caterpillars pupate inside the ants’ nest and the ants continue to look after the pupae. The adult emerges from the pupa after three to four weeks only expanding their wings upon crawling free of the ant’s nest.

4. Reproductive mimicry

Pseudocopulation occurs when a flower mimics a female of a certain insect species, inducing the males to try to copulate with the flower. This is much like the aggressive mimicry in fireflies, but with a more benign outcome for the pollinator. This form of mimicry has been called Pouyannian mimicry, after Maurice-Alexandre Pouyanne, who first described the phenomenon. It is most common in orchids, which mimic females Hymenopterans (generally bees and wasps) and may account for around 60% of pollinations. Depending on the morphology of the flower, a pollen sac pollinium is attached to the head or abdomen of the male. This is then transferred to the stigma of the next flower the male tries to inseminate, resulting in pollination. Visual mimicry is the most obvious sign of this deception for humans, but the visual aspect may be minor or non-existent. It is the senses of touch and olfaction that are most important.

Many orchid species have structures or produce scents that mimic female insects and are attractive to males. Hammer orchids (Genus Drakaea) (Fig 68) are unique in that they are pollinated by a species of male thynnid wasp. Female thynnid wasps are are flightless. When male wasps emerge from the ground, they search for females. When the flightless female wasps emerge, they climb a blade of grass, rub their legs together, release a pheromone and wait for males. When a male detects the pheromone, it flies in a zig-zag pattern upwind until the female is located. The male grasps the female and flies away with her to a food source. Copulation occurs in flight and the male feeds his mate through his abdomen.