Across diverse terrestrial and marine ecosystems, certain organisms bypass cryptic concealment in favor of vivid, ostentatious visual displays. Rather than blending into their ecological backgrounds to avoid detection, these species flaunt high-contrast pigments, contrasting striations, and chromatic patterns that command immediate attention. This biological phenomenon, known as aposematic coloration, represents one of evolutionary biology’s most striking examples of adaptive antipredator signaling, where conspicuous exterior aesthetics serve as honest declarations of unprofitability, chemical toxicity, venomous bites, or formidable mechanical defenses.
Aposematic Coloration
1. Concise Definition
Aposematic coloration, frequently designated as warning coloration, is an antipredator adaptation whereby an organism advertises its physical, chemical, or physiological defenses to potential predators through conspicuous chromatic patterns, stark contrasts, and prominent morphological signals. Unlike cryptic organisms that evade predatory detection entirely, aposematic prey rely on conspicuousness to facilitate predatory recognition, accelerated associative avoidance learning, and long-term memory retention.
In evolutionary biology and behavioral ecology, aposematism operates as an interspecific communication system based on mutual deterrence. The primary ecological function of this coloration is to convert an unpalatable or dangerous organism’s presence into an unambiguous warning. By pairing an overt visual cue with a genuine secondary defense—such as noxious alkaloid secretions, cardiac glycosides, neurotoxins, stinging apparatuses, or foul odors—the prey item mitigates the likelihood of fatal predatory attacks while saving the predator the energetic expense, physical injury, or systemic illness associated with consuming unviable food sources.
2. Etymology & Linguistic Origin
The term aposematism derives from the Classical Greek components απó (apó), meaning “away,” “off,” or “from,” and σῆμα (sêma), denoting a “sign,” “mark,” or “signal.” Compounded together, the construction literally translates to a “sign that turns away” or a “warning signal.”
The concept was formally introduced to the international scientific lexicon in 1890 by the British evolutionary biologist and entomologist Sir Edward Bagnall Poulton in his foundational monograph, The Colours of Animals: Their Meaning and Use, Especially Considered in the Case of Insects. Poulton sought to establish a systematic and rigorous taxonomic nomenclature for biological coloration, distinguishing aposematic (warning) characters from procryptic (protective camouflage), pseudaposematic (false warning, or Batesian mimicry), and synaposematic (shared warning, or Müllerian mimicry) color mechanisms. Through Poulton’s work, the Anglicized noun aposematism and its adjectival forms rapidly superseded colloquial labels such as “terrifying markings” and “flaunting colors.”
3. Pronunciation & Grammatical Form
Pronunciation: The standard International Phonetic Alphabet (IPA) transcription for the term is /ˌæp.ə.sɪˈmæt.ɪk kʌl.əˈreɪ.ʃən/ (British English) or /ˌæp.oʊ.səˈmæt.ɪk ˌkʌl.ɚˈeɪ.ʃən/ (American English). The base noun aposematism is pronounced /ˌæp.əˈsɛm.ə.tɪz.əm/ or /ˌæp.oʊˈsɛm.ə.tɪz.əm/.
Grammatical Structure: “Aposematic coloration” functions syntactically as a compound nominal phrase, composed of the relational adjective aposematic modifying the abstract noun coloration. Morphologically related forms include:
- Noun (Phenomenon): Aposematism
- Noun (Organism): Aposemate
- Adjective: Aposematic
- Adverb: Aposematically
4. Detailed Conceptual Explanation
At its core, aposematic coloration represents an evolutionary compromise between visibility and survival. In standard ecological dynamics, conspicuous visual profiles elevate an organism’s encounter rate with prospective predators. Under traditional Darwinian selection, daylight visibility typically increases mortality. However, when an organism possesses potent secondary defenses—such as secondary chemical metabolites, unpalatable glandular secretions, urticating hairs, stinging venom, or mechanical armor—conspicuousness transforms from an evolutionary liability into an adaptive asset. The visual signal functions as a biological advertisement, reliably forecasting the distasteful or dangerous consequences that await any attacking predator.
The cognitive mechanics underlying aposematism reside largely within predator psychology and neurobiology. Predatory vertebrates, particularly insectivorous birds, mammals, and reptiles, possess sophisticated visual and associative learning capacities. When a naive predator attacks an aposematic prey item, it experiences immediate physiological discomfort, ranging from unpalatable bitterness and emesis to painful envenomation. Because high-contrast patterns (such as alternating black and yellow bands or vibrant scarlet patches) stimulate the predator’s sensory receptors with exceptional intensity, the predator establishes an immediate, durable neurological association between the visual stimulus and the negative visceral feedback. This associative learning diminishes subsequent attacks on phenotypically identical organisms.
Beyond associative learning, aposematic signals frequently exploit innate predatory biases. Many predators demonstrate evolutionary unconditioned avoidance, known as innate aversion, toward specific color combinations, particularly combinations involving intense reds, yellows, and alternating dark bands. Concurrently, predators demonstrate neophobia—a pronounced reluctance to attack, taste, or ingest novel, boldly marked organisms. Consequently, an aposematic organism benefits not only from learned avoidance among experienced resident predators but also from immediate hesitation and wariness exhibited by juveniles or newly arrived foraging predators.
Finally, aposematic signaling functions within an ecological framework governed by natural selection and receiver psychology. Effective warning signals optimize both detectability and discriminability. The signal must stand out starkly against heterogeneous environmental backdrops (high signal-to-noise ratio) and maintain distinct visual separation from benign, edible cohabiting species. By minimizing predatory classification errors, aposematic species avoid the fatal exploratory sampling that often befalls cryptic or ambiguous organisms.
5. Historical Development
The evolutionary origin of warning coloration presented Charles Darwin with an intellectual challenge during the formulation of his evolutionary framework. In 1867, while developing his theory of sexual selection, Darwin recognized that intense, beautiful coloration in male birds and butterflies often arose through mate competition and female choice. However, Darwin was perplexed by the dazzling, kaleidoscopic color patterns displayed by numerous larval insects—specifically caterpillars. Because caterpillars are sexually immature and unable to reproduce in their larval state, their vibrant colors could not be attributed to sexual selection. Moreover, their deliberate visibility appeared fundamentally incompatible with the protective concealment favored by natural selection.
In March 1867, Darwin wrote to his contemporary, the naturalist Alfred Russel Wallace, seeking a plausible evolutionary explanation. Wallace responded with a hypothesis: if caterpillars possessed foul tastes, noxious fluids, or stinging bristles, a bright, conspicuous exterior would serve as an unmistakable badge of unpalatability. Naive predators, having sampled one such individual, would readily remember the striking exterior and subsequently avoid the entire phenotypic class. Darwin was enthusiastic about Wallace’s insight, noting that Wallace had solved what had seemed like an intractable evolutionary paradox.
Over the subsequent two decades, naturalists gathered widespread field evidence. In 1887 and 1889, Edward Bagnall Poulton conducted empirical laboratory experiments using insectivorous lizards, frogs, and birds, systematically validating that brightly colored insects were disproportionately rejected as unpalatable. In 1890, Poulton published The Colours of Animals, formally codifying the term aposematic and integrating warning signals into mainstream evolutionary morphology. During the mid-twentieth century, the population geneticist Ronald A. Fisher expanded the theoretical architecture by demonstrating how warning coloration could evolve via kin selection, resolving the problem of how the initial unpalatable, conspicuous mutants could survive before predator avoidance was fully established.
6. Theoretical Foundations
Modern evolutionary biology models aposematism through an interplay of multiple behavioral and evolutionary frameworks:
Receiver Psychology and Signal Design: Pioneer behavioral ecologists such as Marian Stamp Dawkins and Tim Guilford demonstrated that warning signals are refined by the sensory, perceptual, and cognitive machinery of the receiver (the predator). To achieve evolutionary efficacy, an aposematic signal must satisfy three selective criteria: high detectability (the predator identifies the signal easily across variable ambient lighting), high memorability (the predator retains the associative pairing indefinitely after minimal exposures), and low ambiguity (the predator does not confuse the unpalatable model with edible cryptic prey).
Honest Signaling and Optimal Defense: Within behavioral ecology, aposematism is understood via honest signaling theory. Chemical defenses, such as synthesizing batrachotoxins or sequestering cardenolides, carry significant energetic, metabolic, and ecological costs. Concurrently, displaying conspicuous pigments carries the baseline risk of attracting specialist predators immune to those toxins. Consequently, aposematism operates as an evolutionarily stable strategy (ESS) when the signal’s intensity correlates with the level of secondary unprofitability, ensuring that cheating remains constrained by physiological and ecological trade-offs.
Kin Selection and Spatial Aggregation: A central evolutionary dilemma involves the initial emergence of an aposematic trait: when a conspicuous mutant arises within an otherwise cryptic, unpalatable population, its heightened visibility makes it the first individual to be sampled and killed by a naive predator. Fisher (1930) hypothesized that warning coloration frequently evolves in species that exhibit spatial aggregation or gregariousness among family members. When a naive predator attacks and kills a single conspicuous larva, the predator learns avoidance, thereby sparing the surviving genetically related siblings clustered nearby. Modern evolutionary modeling demonstrates that while kin selection accelerates this evolutionary transition, green-beard effects, synergistic selection, and predator neophobia can also facilitate the evolution of aposematism in solitary species.
7. Key Components, Types & Dimensions
Aposematic systems are multifaceted biological assemblages composed of distinct chromatic, behavioral, and chemical components:
- Chromatic Warning Displays (Visual Modality): The canonical visual presentation characterized by long-wavelength coloration (saturated reds, vivid oranges, bright yellows) contrasted against deep melanic blacks, ultraviolet bands, or iridescent metallic blues. Common motifs include alternating bands, spots, stripes, and reticulated borders.
- Multimodal Aposematism: Warning signals rarely operate through vision alone. Complex aposematic organisms employ complementary sensory channels:
- Acoustic Aposematism: Auditory warning signals, such as the vibrational rattle of pit vipers (Crotalus) or the ultrasonic clicks produced by unpalatable tiger moths (Erebidae) to jam bat biosonar and broadcast chemical distastefulness.
- Olfactory Aposematism: The volatilization of foul-smelling chemical pyrazines, mercaptans, or pungent organic acids (e.g., the pungent defensive spray of skunks or the musky secretions of blister beetles).
- Tonic (Constant) vs. Deimatic (Facultative) Displays: Tonic aposematism involves continuous, permanent manifestation of conspicuous warning signals (e.g., monarch butterflies). In contrast, deimatic or startle displays remain hidden under procryptic outer surfaces until the organism is threatened, at which point vivid eye-spots, bright underwings, or chromatic flashes are abruptly revealed to shock the predator.
- Primary Defenses (The Signal): The morphological phenotype that mediates predatory sensory detection, including color pigments (carotenoids, pterins, ommochromes), structural colors, structural silhouettes, and warning postures.
- Secondary Defenses (The Unprofitability): The underlying biological mechanism that renders the prey harmful or non-viable to ingest, categorized into:
- Autogenous Toxins: Endogenously biosynthesized poisons (e.g., tetrodotoxin in newts, skin alkaloid secretions in salamanders).
- Sequestered Toxins: Phytochemicals harvested from larval host plants and retained into adult life (e.g., cardenolides sequestered by milkweed insects).
- Mechanical and Physical Defenses: Urticating hairs, rigid spines, venomous barbs, dense carapaces, or boiling quinone sprays (e.g., bombardier beetles).
8. Examples & Illustrative Cases
Aposematic coloration is manifested across a wide variety of phylogenetic taxa, showcasing convergent evolution across invertebrates and vertebrates alike:
The Monarch Butterfly (Danaus plexippus): A classical terrestrial example, the adult monarch displays brilliant orange wings laced with black veins and punctuated by white marginal spotting. During its larval stage, the insect feeds exclusively on milkweed plants (Asclepias spp.), sequestering toxic steroids known as cardiac glycosides (cardenolides). These toxins persist through metamorphosis into the adult butterfly. When an avian predator, such as a blue jay (Cyanocitta cristata), consumes a monarch, the cardenolides disrupt sodium-potassium ATPase enzymes in heart muscle, triggering severe cardiac distress and emesis. The surviving bird rapidly forms a long-term conditioned taste aversion, avoiding orange-and-black lepidopterans thereafter.
Poison Dart Frogs (Family Dendrobatidae): Endemic to the humid neotropical rainforests of Central and South America, dendrobatid frogs exhibit extreme phenotypic aposematism. Species such as the golden poison frog (Phyllobates terribilis) and the strawberry poison frog (Oophaga pumilio) present brilliant electric blues, blazing yellows, and crimson tones. Their skin glands contain complex dietary-derived lipophilic alkaloids, including batrachotoxin and histrionicotoxin, which act as potent voltage-gated sodium channel activators and neurotoxins capable of inducing systemic paralysis and respiratory arrest in vertebrate predators.
Coral Snakes (Genus Micrurus): Venomous elapid snakes throughout the Western Hemisphere exhibit striking alternating rings of red, yellow (or white), and black. Their potent neurotoxic venom causes rapid neuromuscular blockade and death in mammalian and avian predators. This warning display is so biologically effective that it anchors extensive mimicry complexes, with dozens of non-venomous colubrid snakes (such as milk snakes and king snakes) evolving matching color bands to deceive predators.
The Blue-Ringed Octopus (Genus Hapalochlaena): Within marine ecosystems, the blue-ringed octopus inhabits Indo-Pacific tide pools and coral reefs. While typically camouflaged against rocky substrates, when provoked or stressed, its dermal chromatophores rapidly illuminate iridescent, electric-blue rings across its mantle and tentacles. These pulsating rings broadcast the presence of tetrodotoxin (TTX), a potent neurotoxin produced by endosymbiotic salivary bacteria capable of inducing human respiratory paralysis within minutes.
Striped Skunks (Mephitis mephitis): Aposematic coloration is not restricted to ectotherms. Mammalian carnivorans frequently adopt bold, starkly contrasting black-and-white longitudinal stripes. The striped skunk advertises its anal scent glands, which discharge an aerosolized mixture of volatile thiols and thioacetates. The visual contrast against nocturnal backgrounds reliably deters predatory coyotes, wolves, and domestic dogs from initiating an encounter.
9. Measurement & Assessment
Historically, evaluating animal coloration relied on subjective human visual perception—an approach fundamentally flawed due to human trichromatic vision lacking ultraviolet sensitivity and possessing distinct spectral sensitivities compared to avian, reptilian, and insect predators. Contemporary behavioral ecologists utilize rigorous, objective analytical techniques:
Reflectance Spectrophotometry: Researchers employ portable UV-visible spectrophotometers to quantify the absolute physical properties of light reflected from an organism’s integument across wavelengths from 300 to 700 nanometers. This objective metric captures ultraviolet reflectance patterns that remain invisible to the human eye but are salient to predatory birds and arthropods.
Visual Modeling and Receptor Noise Models: To determine whether a color pattern functions aposematically, scientists utilize physiological visual models—most notably the Vorobyev-Osorio receptor-noise model. By mapping calibrated spectral reflectance curves against the known cone photoreceptor sensitivities and ocular transmission media of specific predators (e.g., passerine birds with ultraviolet-sensitive [UVS] or violet-sensitive [VS] cones), researchers compute chromatic contrast ($\Delta S$) and achromatic luminance contrast ($\Delta L$) in units of “Just Noticeable Differences” (JNDs). Values exceeding established thresholds indicate that a signal is perceptually distinct and conspicuous to that specific receiver’s sensory visual system.
Quantification of Secondary Defenses: Aposematism requires demonstrating that secondary unprofitability exists alongside visual distinctiveness. Researchers quantify toxicity through analytical chemistry techniques, including high-performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS), and bioassays measuring the median lethal dose (LD50) or emetic response units in standard laboratory models.
Behavioral and Cognitive Bioassays: Controlled operant conditioning chambers, artificial arena experiments, and field trials using plasticine prey replicas are used to assess predator learning rates, survival probabilities, and the persistence of learned avoidance behavior across diverse background conditions.
10. Applications & Practical Significance
The principles of aposematic coloration extend far beyond evolutionary biology, shaping design engineering, industrial ergonomics, and public safety:
Occupational Safety and Hazard Warning Systems: Human safety iconography directly mirrors biological aposematism. Industrial safety signs, high-voltage warnings, toxic chemical placards, and radiation hazard symbols universally adopt high-contrast yellow-and-black stripes or bold orange-and-black matrices. Graphic designers utilize the human visual system’s innate perceptual sensitivity to these contrast dynamics, maximizing reaction speed and minimizing cognitive processing time in high-risk environments.
Bio-Inspired Materials and Cryptic Deterrence: In maritime recreation, wetsuit and surfboard designers have engineered anti-shark deterrent suits based on aposematic and banding motifs. Incorporating high-contrast black-and-white striations reminiscent of venomous sea snakes (Hydrophiinae), these garments aim to leverage potential predatory hesitance or neophobia in apex predators such as great white sharks (Carcharodon carcharias).
Pharmacological and Biomedical Bioprospecting: Aposematic organisms serve as visual indicators for pharmacologically active natural products. Because vibrant warning signals regularly correlate with novel biological poisons, medical researchers systematically target aposematic species for bioprospecting. Investigations into dendrobatid frogs, sea slugs (Nudibranchia), and cone snails have yielded valuable analgesics, neuromuscular blocking agents, ion channel modulators, and non-opioid pain therapeutics (such as ziconotide).
Agricultural Pest Management: Understanding aposematic dynamics assists agroecologists in designing integrated pest management (IPM) strategies. Monitoring pest species that exhibit warning signals (such as certain aposematic aphids or true bugs) aids in predicting secondary poisoning risks for beneficial biological control agents, including parasitic wasps and ladybird beetles (Coccinellidae).
11. Research & Empirical Evidence
Decades of field experiments, laboratory trials, and mathematical modeling have generated empirical insights into the functional ecology of warning signals:
The Evolution of Warning Signals: Groundbreaking work by John Endler, Tim Guilford, and Michael Speed addressed how aposematic displays function across varied physical environments. Research by James Mallet and Mathieu Joron documented that within neotropical butterfly clades (e.g., Heliconius), aposematism is maintained by intense stabilizing selection driven by local predator communities. Alterations in warning coloration away from regional warning morphs result in elevated predation rates by wild insectivorous birds.
Predator Cognition and Multi-Component Signals: Experimental work led by Candy Rowe and John Skelhorn demonstrated that multimodal warning displays—combining visual patterns with sound or odor—accelerate associative learning in naive predators while reducing the rate at which experienced predators commit recognition errors. Their findings show that olfactory pyrazines emitted by certain aposematic insects trigger unconditioned wariness and accelerate color-avoidance learning in predatory chicks.
Spatial Distribution and Automimicry: Lincoln Brower’s classic long-term empirical investigations into the chemical ecology of the monarch butterfly revealed the phenomenon of automimicry. Brower demonstrated that because milkweed plants vary widely in cardenolide concentrations, wild monarch populations are heterogeneous: some individuals are lethally toxic, while others contain few or no cardenolides. Brower showed that palatable individuals survive by masquerading as their toxic conspecifics, maintaining an evolutionarily stable system provided that the ratio of palatable automimics does not exceed the threshold where predators unlearn avoidance.
12. Cultural & Cross-Cultural Considerations
The salient visual cues of aposematic organisms have influenced human cultural symbolism, traditional folklore, and indigenous knowledge across the globe:
Indigenous Ecological Knowledge: For centuries, indigenous communities living in tropical biomes have recognized and utilized aposematic dynamics. Indigenous hunters of the Emberá and Chocó peoples of western Colombia possess extensive ethnozoological knowledge regarding the dermal secretions of Phyllobates poison frogs, harvesting their batrachotoxins to prepare lethal blowgun darts for hunting arboreal game. Their cultural taxonomies accurately identify the correlations between chromatic intensity, habitat variations, and venom lethality.
Mythology, Heraldry, and Cultural Semiotics: Across diverse human societies, high-contrast black-and-yellow or red-and-black coloration has accrued universal cultural associations with danger, toxicity, and boundary demarcation. In European folklore and heraldry, spotted salamanders and fiery serpents were frequently associated with elemental fire and poison. In contemporary popular culture, toxic entities in video games, graphic novels, and cinema are regularly depicted with bright aposematic color palettes, demonstrating how human artistic tropes intuitively draw upon biological antipredator systems.
13. Criticisms, Debates & Limitations
Despite its conceptual foundations, aposematism remains a subject of debate within evolutionary biology, centering on several unresolved theoretical and empirical questions:
The Paradox of the First Mutant: How can a conspicuous, unpalatable mutant survive long enough to establish an aposematic population? Because predatory avoidance requires prior learning, the very first brightly colored mutant in an ancestral cryptic population should experience high predation rates. While models invoking kin selection, family grouping, and predator neophobia provide potential resolutions, scientists continue to debate whether aposematism primarily evolves through gradual shifts in conspicuousness or via sudden macro-mutations buffered by maternal effects and habitat selection.
Imperfect Mimicry and Signal Variability: Evolutionary models predict that natural selection should drive warning signals toward narrow, invariant optima to facilitate predator recognition. Yet, pervasive phenotypic variation and imperfect mimicry persist throughout nature. Numerous harmless hoverflies (Syrphidae) only crudely resemble stinging wasps (Vespidae), yet they persist in vast numbers. Competing hypotheses suggest that imperfect mimics survive because multi-prey environments impose cognitive processing limits on predators, or because the severe fitness costs of a wasp sting make predators overcautious, tolerating approximate resemblances.
The Distance-Dependent Conspicuousness Hypothesis: Recent research challenges the assumption that aposematic organisms are conspicuous across all spatial scales. The distance-dependent aposematism hypothesis suggests that certain color patterns operate dual-functionally: appearing cryptic from a distance due to spatial visual blending, but transforming into high-contrast warning signals when viewed up close by an approaching predator. This gradient challenges traditional binary distinctions between camouflage and aposematism.
14. Related Terms & Distinctions
To accurately understand aposematic coloration, it must be differentiated from closely related ecological and evolutionary concepts:
- Aposematism vs. Crypsis (Camouflage): Crypsis aims to prevent an organism from being detected by matching environmental textures, patterns, and background coloration. In contrast, aposematism ensures that the organism is readily detected and identified, relying on unprofitability rather than concealment for survival.
- Aposematism vs. Batesian Mimicry: An aposematic organism is an honest model possessing genuine defenses. A Batesian mimic is an edible, defenseless organism that parasitizes the warning signal of an aposematic model to deceive shared predators.
- Aposematism vs. Müllerian Mimicry: Müllerian mimicry involves two or more distinct unpalatable, aposematic species that evolve convergent, shared warning patterns. By pooling their visual advertisements, they share the ecological cost of educating the local predator community.
- Aposematism vs. Deimatic (Startle) Displays: While aposematism broadcasts genuine unprofitability (often continuously), deimatic displays involve sudden behavioral transitions—such as flashing concealed eye-spots or expanding thorax margins—designed to startle, disorient, or bluff a predator, regardless of whether the prey possesses a secondary defense.
- Aposematism vs. Masquerade: Masquerade occurs when an organism evolves morphological resemblance to an uninteresting, inedible object (such as a dead leaf, bird dropping, or twig). Predators detect the organism but misclassify it as non-biological, whereas aposematic organisms are recognized directly as hazardous biological prey.
15. Summary / Key Takeaways
Aposematic coloration serves as an antipredator mechanism characterized by conspicuous chromatic signals that advertise genuine chemical, physical, or physiological defenses. First theorized by Alfred Russel Wallace and formally designated by Edward Bagnall Poulton in 1890, the trait addresses an evolutionary trade-off by turning high visibility into a survival advantage through predator psychology and associative learning.
The evolutionary persistence of aposematism relies on honest signaling, receiver memorability, and the cognitive constraints of foraging predators. From monarch butterflies and neotropical dendrobatid frogs to venomous coral snakes and striped skunks, aposematism illustrates the convergent coordination of anatomy, physiology, and behavior. While theoretical debates persist regarding the origin of initial mutations and the persistence of imperfect mimicry, aposematism remains a cornerstone model in modern evolutionary theory, shaping our understanding of animal communication, cognitive ecology, and bio-inspired design.
References
- Fisher, R. A. (1930). The Genetical Theory of Natural Selection. Oxford University Press.
- Guilford, T. (1990). The evolution of aposematism. In D. L. Evans & J. O. Schmidt (Eds.), Insect Defenses: Adaptive Mechanisms and Strategies of Prey and Predators (pp. 23–61). State University of New York Press.
- Mallet, J., & Joron, M. (1999). Evolution of diversity in warning color and mimicry: Polymorphisms, shifting balance, and speciation. Annual Review of Ecology and Systematics, 30(1), 201–233.
- Poulton, E. B. (1890). The Colours of Animals: Their Meaning and Use, Especially Considered in the Case of Insects. Kegan Paul, Trench, Trübner & Co.
- Rowe, C., & Guilford, T. (1999). The evolution of multimodal warning displays. Evolutionary Ecology, 13(7), 655–671.
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- Wallace, A. R. (1867). Proceedings of the Entomological Society of London. Transactions of the Entomological Society of London, 3(4), lxxx–lxxxi.