Prey Transport Mechanisms in Blindsnakes and the Evolution of Unilateral Feeding Systems in Snakes

Most snakes ingest and transport their prey via a jaw ratchetingmechanism in which the left and right upper jaw arches are advancedover the prey in an alternating, unilateral fashion. This unilateraljaw ratcheting mechanism differs greatly from the hyolingualand inertial transport mechanisms used by lizards, both of whichare characterized by bilaterally synchronous jaw movements.Given the well-corroborated phylogenetic hypothesis that snakesare derived from lizards, this suggests that major changes occurredin both the morphology and motor control of the feeding apparatusduring the early evolution of snakes. However, most previousstudies of the evolution of unilateral feeding mechanisms insnakes have focused almost exclusively on the morphology ofthe jaw apparatus because there have been very few direct observationsof feeding behavior in basal snakes. In this paper I describethe prey transport mechanisms used by representatives of twofamilies of basal snakes, Leptotyphlopidae and Typhlopidae.In Leptotyphlopidae, a mandibular raking mechanism is used,in which bilaterally synchronous flexions of the lower jaw serveto ratchet prey into and through the mouth. In Typhlopidae,a maxillary raking mechanism is used, in which asynchronousratcheting movements of the highly mobile upper jaws are usedto drag prey through the oral cavity. These findings suggestthat the unilateral feeding mechanisms that characterize themajority of living snakes were not present primitively in Serpentes,but arose subsequently to the basal divergence between Scolecophidiaand Alethinophidia.     

Influence of the venom delivery system on intraoral prey transport in snakes

We compared intraoral prey transport in venomous snake species from four families (two atractaspidids, nine elapids, three colubrids, 44 viperids) with that in eight non-venomous colubrid species, most feeding on similar mammalian prey. The morphology of the venom delivery system suggests that intraoral prey transport performance should be slightly decreased in atractaspidids, unmodified in most elapids and venomous colubrids, and increased or unmodified in vipers, as compared to that in non-venomous colubrid snakes. Our measurements of relative intraoral prey transport performance show that differences among families do not match expectations based on morphology or past studies. Decreased performance in Atractaspis results from reduction and loss of teeth on the medial palatal elements and dentaries, but affects only early phases of ingestion. Although joint and bone features of elapids and colubrids are similar, intraoral prey transport performance is significantly lower in elapids than in colubrids. Predicted enhancement of intraoral prey transport performance in vipers as compared to colubrids was not borne out by measurements, presumably because palatopterygoid movement during intraoral prey transport is reduced in many viper species to limit fang erection. Absence of significant performance differences between colubrids and viperids might suggest that evolution of the viperid venom delivery system was subject to little selection pressure from intraoral prey transport. Another possibility is that there are trade-offs between intraoral prey transport and strike performance in vipers related to relative skull mass and jaw fragility. Immobilizing prey prior to intraoral transport places less demand on transport performance in vipers. In this model, the conservative kinesis and greater robustness of the colubrid palate has greater potential for transporting live prey with less risk of injury.     

The functional meaning of “prey size” in water snakes (Nerodia fasciata, Colubridae)

The evolutionary success of macrostomatan (enlarged-gape) snakes has been attributed to their ability to consume large prey, in turn made possible by their highly kinetic skulls. However, prey can be “large” in several ways, and we have little insight into which aspects of prey size and shape affect skull function during feeding. We used X-ray videos of broad-banded water snakes (Nerodia fasciata) feeding on both frogs and fish to quantify movements of the jaw elements during prey transport, and of the anterior vertebral column during post-cranial swallowing. In a sample of additional individuals feeding on both frogs and fish, we measured the time and the number of jaw protractions needed to transport prey through the buccal cavity. Prey type (fish vs. frog) did not influence transport kinematics, but did influence transport performance. Furthermore, wider and taller prey induced greater movements of most cranial elements, but wider prey were transported with significantly less anterior vertebral bending. In the performance trials, heavier, shorter, and wider prey took significantly more time and a greater number of jaw protractions to ingest. Thus, the functional challenges involved in prey transport depend not only upon prey mass, but also prey type (fish vs. frog) and prey shape (relative height, width and length), suggesting that from the perspective of a gape-limited predator, the difficulty of prey ingestion depends upon multiple aspects of prey size.     

Do lizards and snakes really differ in their ability to take large prey? A study of relative prey mass and feeding tactics in lizards

Adaptations of snakes to overpower and ingest relatively large prey have attracted considerable research, whereas lizards generally are regarded as unable to subdue or ingest such large prey items. Our data challenge this assumption. On morphological grounds, most lizards lack the highly kinetic skulls that facilitate prey ingestion in macrostomate snakes, but (1) are capable of reducing large items into ingestible-sized pieces, and (2) have much larger heads relative to body length than do snakes. Thus, maximum ingestible prey size might be as high in some lizards as in snakes. Also, the willingness of lizards to tackle very large prey items may have been underestimated. Captive hatchling scincid lizards (Bassiana duperreyi) offered crickets of a range of relative prey masses (RPMs) attacked (and sometimes consumed parts of) crickets as large as or larger than their own body mass. RPM affected foraging responses: larger crickets were less likely to be attacked (especially on the abdomen), more likely to be avoided, and less likely to provide significant nutritional benefit to the predator. Nonetheless, lizards successfully attacked and consumed most crickets ≤35% of the predator’s own body mass, representing RPM as high as for most prey taken by snakes. Thus, although lizards lack the impressive cranial kinesis or prey-subduction adaptations of snakes, at least some lizards are capable of overpowering and ingesting prey items as large as those consumed by snakes of similar body sizes.     

Why do Juvenile Chinese Pit‐Vipers (Gloydius shedaoensis) Select Arboreal Ambush Sites?

Ontogenetic shifts in habitat use are widespread, especially in ectothermic taxa in which juveniles may be an order of magnitude smaller than large adult conspecifics. The factors that generate such habitat shifts are generally obscure, but we studied an unusual system that allowed us to compare consequences of habitat selection between adults and juveniles. Pit‐vipers (Gloydius shedaoensis) on a small island in north‐eastern China feed almost entirely on seasonally migrating birds. During the spring bird‐migration period, individual snakes consistently re‐used either arboreal or terrestrial ambush sites. Snakes in trees were smaller (and more philopatric) than snakes on the ground. This ontogenetic shift in habitat use may reflect the difficulty of capturing birds on the ground, especially by small snakes. In laboratory trials, large (adult) pit‐vipers struck faster, further and more accurately than did small (juvenile) snakes. In experiments with free‐ranging snakes, the proportion of strikes hitting the bird was lower for juveniles than for adults, and lower for terrestrial snakes than for arboreal snakes. Additionally, adult snakes generally seized the bird by the head whereas juveniles frequently struck the body or wings (and thus, obtained a less secure grip). Arboreal ambush sites may facilitate prey capture not only because they give access to smaller birds but also because they render the bird's location more predictable and, hence, enable the snake to position itself optimally prior to the prey's arrival. Because juvenile pit‐vipers are less capable strikers, and are small relative to available prey items, they may benefit from the greater ease of prey capture from branches. Thus, the ontogenetic shift in habitat selection within this species may be because of ontogenetic shifts in the vipers’ ability to capture and ingest large, mobile prey.     

Melanin deposits associated with the venom glands of snakes

Melanin deposits in the heads of both true vipers (Viperinae) and pit vipers (Crotalinae) are concentrated over the dorsal and dorsolateral aspects of the venom glands. This pigment may occur in any or all of six sites which include the epidermis, dermis, tissues covering the venom glands, and the interior of the glands themselves. The extreme localization of these melanin deposits suggests that they shield the venom glands from light. Calculations indicate that without such shielding the light energy penetrating the venom glands in the visible and ultraviolet portions of the solar spectrum would damage the venom-synthesizing apparatus and detoxify stored venom. Elapid and hydrophiid snakes have less dense pigment over the venom gland than vipers. Literature reports indicate that elapid venom is less sensitive to photodetoxification than is venom from vipers. Most colubrid snakes, including several with protein-secreting Duvernoy's glands, have little or no melanin associated with the glands. Venomous colubrids in the genera Ahaetulla, Dryophis, Leptophis, and Oxybelis have pigment over the glands as dense as that seen in vipers. Iridophores probably also shield venom glands from radiation. In puff adders and Gaboon vipers (Bitis) there appears to be an ontogenetic change in the shielding of the venom glands from melanocytes in young individuals to iridophores in adults.     

Effects of dissociating agents on the fine structure of embryonic chick thyroid cells

Heads of the boid snakes Python sebae and Python molurus were dissected and the arthrology, myology and dentition studied. Living specimens of these species were observed and their feeding behavior analyzed by means of high- and regular-speed motion pictures. Camera speeds of up to 400 frames per second permitted examination of the jaw movements during the striking and seizing of prey. Motion picture studies conducted at regular speeds provided information on cranial movements during the swallowing of prey. The morphology of the head was correlated with observed movements in an attempt to analyze the functional and adaptive implications of the jaw apparatus. The cranial apparatus was discussed in terms of a linkage or kinematic chain whose constrainment and degrees of freedom were examined and compared with the jaw linkage of lizards. It was concluded that the very rigidly constrained mechanism in lizards is in remarkably sharp contrast to the very loose apparatus in snakes. Motions of various cranial bones were analyzed with particular attention given the mechanical factors involved. In full protraction the maxillae and palatines are lifted and rotated outward about a longitudinal axis. These movements are important in orienting the teeth with respect to the prey and are related to seizing and swallowing.     

Antipredatory function of head shape for vipers and their mimics

Most research into the adaptive significance of warning signals has focused on the colouration and patterns of prey animals. However, behaviour, odour and body shape can also have signal functions and thereby reduce predators' willingness to attack defended prey. European vipers all have a distinctive triangular head shape; and they are all venomous. Several non-venomous snakes, including the subfamily Natricinae, commonly flatten their heads (also known as head triangulation) when disturbed. The adaptive significance of this potential behavioural mimicry has never been investigated.We experimentally tested if the triangular head shape typical of vipers offers protection against predation. We compared the predation pressure of free-ranging predators on artificial snakes with triangular-shaped heads against the pressure on replicas with narrow heads. Snakes of both head types had either zigzag patterned bodies, typical of European vipers, or plain (patternless) bodies. Plain snakes with narrower Colubrid-like heads suffered significantly higher predation by raptors than snakes with triangular-shaped heads. Head shape did not, however, have an additive effect on survival in zigzag-patterned snakes, suggesting that species which differ from vipers in colouration and pattern would benefit most from behavioural mimicry. Our results demonstrate that the triangular head shape typical of vipers can act as a warning signal to predators. We suggest that head-shape mimicry may be a more common phenomenon among more diverse taxa than is currently recognised.     

Feeding behaviour in Cylindrophis and its bearing on the evolution of alethinophidian snakes

Cylindrophis ruffus ingests prey using two distinct mechanisms. During initial phases of prey transport, lateral movements of the rear of the braincase combine with small unilateral movements of the toothed bones of each side; prey is usually constricted during this phase to permit the snake to push its head over the prey. Once transport has carried the leading part of the prey into the anterior oesophagus, Cylindrophis begins to use bilaterally synchronized movements of the jaw apparatus combined with low-amplitude, short wave-length flexions of the anterior vertebral column. Transport of prey is many times faster during the bilateral phase than during the unilateral phase.
Radiographic and cinematographic evidence indicates that the mandibular tips of Cylindrophis do not separate more than 1.5–2.0 times the resting distance between the dentary tips. Although this limits potential gape size, the intramandibular joint is highly mobile, allowing the mandibles to conform to a variety of prey shapes. Manipulations of anaesthetized and fresh, dead specimens revealed that the palatomaxillary arches are tightly attached to the ventral bones of the snout, movements of each arch being reflected in equivalent movements of the ipsilateral elements of the snout.
Cylindrophis represents a functional stage intermediate between most lizards with limited palatomaxillary kinesis and advanced snakes with considerable palatomaxillary mobility. Contrary to previous hypotheses, however, upper jaw liberation in Cylindrophis is due to liberation of the ventral snout, not to reduction of attachments to the braincase and snout. This suggests that the nose played a crucial role in the evolution of the feeding apparatus in alethinophidian snakes.     

Strike-induced chemosensory searching in venomoid pit vipers at Hogle Zoo

Six pit vipers with ligated and severed venom ducts were each observed twice. In the no-strike trial a rodent was presented for 3 sec but held (on tongs) out of striking range. The strike trial began with a 3 sec presentation, but the prey item was then moved into striking range, and all snakes immediately struck and released the rodents. Prey were removed after no-strike and strike presentations and the rate of tongue flicking was recorded for 30 min. Only strike presentations were followed by high rates of tongue flicking, which were indistinguishable from those seen in pit vipers with functioning venom apparatus. We conclude that venom injection is irrelevant for the causation of strike-induced chemosensory searching.     

Comparison of cranial form and function in association with diet in natricine snakes

The skull of squamates has many functions, with food acquisition and ingestion being paramount. Snakes vary interspecifically in the frequency, size, and types of prey that are consumed. Natural selection should favor phenotypes that minimize the costs of energy acquisition; therefore, trophic morphology should reflect a snake's primary prey type to enhance some aspect of feeding performance. I measured 19 cranial variables for six natricine species that vary in the frequency with which they consume frogs and fish. Both conventional and phylogenetically corrected analyses indicated that fish‐eating snakes have relatively longer upper and lower jaw elements than frog‐eating snakes, which tended to have broader skull components. I also compared the ratio of the in‐lever to the out‐lever lengths of the jaw‐closing mechanism [jaw mechanical advantage (MA)] among species. Fish‐eating snakes had significantly lower MAs in the jaws than did the frog‐eating snakes. This result suggests that piscivores have faster closing jaws and that the jaws of frog‐eating snakes have higher closing forces. Cranial morphology and the functional demands of prey capture and ingestion appear to be associated with primary prey type in natricine snakes. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

Functional and Numerical Responses of Predators: Where Do Vipers Fit in the Traditional Paradigms?

Snakes typically are not considered top carnivores, yet in many ecosystems they are a major predatory influence. A literature search confirmed that terrestrial ectotherms such as snakes are largely absent in most discussions of predator‐prey dynamics. Here, we review classical functional and numerical responses of predator‐prey relationships and then assess whether these traditional views are consistent with what we know of one group of snakes (true vipers and pitvipers: Viperidae). Specifically, we compare behavioural and physiological characteristics of vipers with those of more commonly studied mammalian (endothermic) predators and discuss how functional and numerical responses of vipers are fundamentally different. Overall, when compared to similar‐sized endotherms, our analysis showed that vipers have: (i) lower functional responses owing primarily to longer prey handling times resulting from digestive limitations of consuming large prey and, for some adults, tolerance of fasting; (ii) stronger numerical responses resulting from higher efficiency of converting food into fitness currency (progeny), although this response often takes longer to be expressed; and (iii) reduced capacity for rapid numerical responses to short‐term changes in prey abundance. Given these factors, the potential for viperids to regulate prey populations would most likely occur when prey populations are low. We provide suggestions for future research on key issues in predator‐prey relationships of vipers, including their position within the classical paradigms of functional and numerical responses.     

Prey envenomation does not improve digestive performance in Taiwanese pit vipers (Trimeresurus gracilis and T. stejnegeri stejnegeri)

It has been a common belief that snake venom may help in the digestion of its prey, although direct examples and supporting evidence have not been sufficient. To address this, the present study examined whether pre-injecting natural amounts of pit viper venom into experimental mice may accelerate their digestion by the snakes or gain energy benefit as compared to the control without the envenomation. Live adults of two Asian pit viper species Trimeresurus gracilis and T. stejnegeri stejnegeri, which inhabit the cold and warm environment respectively, were the subjects studied herein. A natural dose of 1.2 mg of each of the pit viper venom in phosphate-buffered saline (PBS) was injected into the mouse (about 10% of the snake mass) before it was being fed to the same species of vipers, while the pit vipers in control group were given mouse injected with sterile PBS. The snakes were kept at 14 °C or 24 °C, and parameters of gut passage time, costs of digestion, and/or digestive efficiency were measured. The results did not support the hypotheses that envenomation facilitates prey digestion. The venom in fact caused longer first defecation time and lower assimilation energy at 14 °C. Besides, the time to reach the oxygen consumption peak, and the first defecation time of T. s. stejnegeri were longer than that of T. gracilis.     

Proteolytic activity of viper venoms

Proteolytic activities of venoms of vipers kept in a serpentarium for three years or captured in various environmental regions were estimated. Gurza venom contained considerable amounts of protein (830-930 micrograms/mg venom) and displayed a high proteolytic activity by tyrosine (80-140 micrograms/min mg protein). The proteolytic activity did not depend on season, as well as age or physiological state of snakes in the reproductive period. The proteolytic activity of venom in gurza offspring was similar to that in parent specimens. Proteolytic activities (by tyrosine) of venoms produced by Radde's vipers and common vipers were 77-90 and 18-36 micrograms/min mg protein, respectively. The proteolytic activity of venom in common vipers native to the north European part of Russia was 20-30% higher than that in common vipers inhabiting southern European Russia. An inhibition assay found various ratios of metalloendopeptidase and serine endopeptidase activities in venoms of gurza, Radde's viper, and common viper.     

Morphological integration and adaptation in the snake feeding system: a comparative phylogenetic study

A long-standing hypothesis for the adaptive radiation of macrostomatan snakes is that their enlarged gape--compared to both lizards and basal snakes--enables them to consume "large" prey. At first glance, this hypothesis seems plausible, or even likely, given the wealth of studies showing a tight match between maximum consumed prey mass and head size in snakes. However, this hypothesis has never been tested within a comparative framework. We address this issue here by testing this hypothesis in 12 monophyletic clades of macrostomatan snakes using recently published phylogenies, published maximum consumed prey mass data and morphological measurements taken from a large sample of museum specimens. Our nonphylogenetically corrected analysis shows that head width--independent of body size--is significantly related to mean maximum consumed prey mass among these clades, and this relationship becomes even more significant when phylogeny is taken into account. Therefore, these data do support the hypothesis that head shape is adapted to prey size in snakes. Additionally, we calculated a phylogenetically corrected morphological variance-covariance matrix to examine the role of morphological integration during head shape evolution in snakes. This matrix shows that head width strongly covaries with both jaw length and out-lever length of the lower jaw. As a result, selection on head width will likely be associated with concomitant changes in jaw length and lower jaw out-lever length in snakes.     

Post-cranial prey transport mechanisms in the black pinesnake, Pituophis melanoleucus lodingi: an x-ray videographic study

Most previous studies of snake feeding mechanisms have focused on the functional morphology of the highly specialized ophidian jaw apparatus. Although some of these studies have included observations of post-cranial movements during feeding, the functional roles of these movements have remained poorly understood. In this study, we used x-ray videography to examine post-cranial prey transport mechanisms in a colubrid snake, Pituophis melanoleucus lodingi. We found that prey transport in this species progresses through four distinct phases, three of which are characterized by either undulatory or concertina-like movements of the anterior portion of the trunk. In the first phase of transport (the oral phase), unilateral movements of the jaws are used to pull the head forward around the prey. In the second phase (the orocervical phase), unilateral jaw movements continue, but are augmented by concertina-like movements of the anterior portion of the trunk. In the third phase (the cervical phase), prey transport occurs exclusively through concertina-like movements of the neck. Finally, in the fourth phase (the thoracic phase), prey is transported to the stomach via undulatory movements of the trunk. Our observations of feeding behavior in a phylogenetically diverse sample of fourteen other snake species demonstrate that similar post-cranial transport mechanisms are used by a wide variety of alethinophidian snakes that feed on large, bulky prey.     

Functional plasticity of the venom delivery system in snakes with a focus on the poststrike prey release behavior

We explored variations in the morphology and function of the envenomation system in the four families of snakes comprising the Colubroidea (Viperidae, Elapidae, Atractaspididae, and Colubridae) using our own prey capture records and those from the literature. We first described the current knowledge of the morphology and function of venom delivery systems and then explored the functional plasticity found in those systems, focusing on how the propensity of snakes to release prey after the strike is influenced by various ecological parameters. Front-fanged families (Viperidae, Elapidae, and Atractaspididae) differ in the morphology and topographical relationships of the maxilla as well as in the lengths of their dorsal constrictor muscles (retractor vomeris; protractor, retractor, and levator pterygoidei; protractor quadrati), which move the bones comprising the upper jaw, giving some viperids relatively greater maxillary mobility compared to that of other colubroids. Rear-fanged colubrids vary in maxillary rotation capabilities, but most have a relatively unmodified palatal morphology compared to non-venomous colubrids. Viperids launch rapid strikes at prey, whereas elapids and colubrids use a variety of behaviors to grab prey. Viperids and elapids envenomate prey by opening their mouth and rotating both maxillae to erect their fangs. Both fangs are embedded in the prey by a bite that often results in some retraction of the maxilla. In contrast, Atractaspis (Atractaspididae) envenomates prey by extruding a fang unilaterally from its closed mouth and stabbing it into the prey by a downward-backwards jerk of its head. Rear-fanged colubrids envenomate prey by repeated unilateral or bilateral raking motions of one or both maxillae, some aspects of which are kinematically similar to the envenomation behavior in Atractaspis. The envenomation behavior, including the strike and prey release behaviors, varies within families as a function of prey size and habitat preference. Rear-fanged colubrids, arboreal viperids, and elapids tend to hold on to their prey after striking it, whereas atractaspidids and many terrestrial viperids release their prey after striking it. Larger prey are more frequently released than smaller prey by terrestrial front-fanged species. Venom delivery systems demonstrate a range of kinematic patterns that are correlated to sometimes only minor modifications of a common morphology of the jaw apparatus. The kinematics of the jaw apparatus are correlated with phylogeny, but also show functional plasticity relating to habitat and prey.     

What,if anything,is a ‘typical’ viper? Biological attributes of basal viperid snakes (genus Causus Wagler, 1830)

For many major phylogenetic radiations of organisms, the available ecological knowledge is disproportionately derived from a small minority of taxa, and sometimes from organisms that are highly atypical. Viperid snakes provide a good example of this situation; high-latitude cold-climate taxa in northern Europe (vipers) and North America (rattlesnakes) have been studied intensively, but more speciose radiations in tropical Africa, Asia, and Central America remain poorly known. We dissected > 500 specimens (six species) of night adders (genus Causus ), mostly from Cameroon (68%) in equatorial Africa, to quantify morphology, diets, and reproductive biology. By contrast to the 'slow' life-histories of cold-climate viperids, night adders feed frequently on frogs (rather than infrequently on mammals), and produce frequent large clutches of relatively small eggs (rather than infrequent small litters of relatively large live young). Thus, putatively 'typical' viperid attributes such as low fecundity, viviparity, and predation on mammals reflect adaptations to the invasion of cold environments by a small and perhaps atypical subset of viperid taxa. Our data on prey size suggest that one of the critical innovations of early viperids may have been an ability to subdue and ingest relatively large prey.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 575–588.     

后毒牙类毒蛇

长期以来,人们仅把具有沟牙和管牙的蛇视为毒蛇,然而,近年来发现游蛇科中的虎斑颈槽蛇、红脖颈槽蛇、颈棱蛇、赤链蛇等既无管牙,也无沟牙,却频频发生这类蛇咬伤人后引起中毒的事例,甚至出现被咬伤致严重出血休克死亡的事件。经深入研究后发现,这些蛇虽没有沟牙和管牙,但却具有产生毒性分泌物的毒腺—杜氏腺(Duvernoy′s gland)及皮下腺,且不同的毒腺具有不同的毒性作用,可表现为出血不止、溶血、呼吸困难、肾损害等。这类蛇与毒腺的导管有联系的上颌牙明显粗大,上颌牙与上颌骨、横骨连接牢固,毒腺里的毒液可顺着粗大的上颌牙流入伤口,因此,应视为"后毒牙类毒蛇"。     

The snake hiss: potential acoustic mimicry in a viper–colubrid complex

Examples of acoustic Batesian mimicry are scarce, in contrast to visual mimicry. Here we describe a potential case of acoustic mimicry of a venomous viper model by harmless viperine snakes (colubrid). Viperine snakes resemble vipers in size, shape, colour, pattern, and anti‐predatory behaviours, including head flattening, false strikes, and hissing. We sought to investigate whether hissing evolved as part of, or separately to, the viper mimic syndrome. To do this, we recorded and analysed the hissing sounds of several individual asp vipers, viperine snakes, and grass snakes (a close relative of viperine snakes that hisses but does not mimic the asp viper). Frequencies consistently ranged from 40 to 12 000 Hz across species and individuals. All vipers (100%) and most viperine snakes (84%) produced inhalation hissing sounds, in comparison to only 25% of grass snakes. Inhalation hissing sounds lasted longer in vipers than in viperine snakes. The hissing‐sound composition of grass snakes differed significantly from that of both asp vipers and viperine snakes; however, the hissing‐sound composition between viperine snakes and asp vipers was not statistically distinguishable. Whilst grass snake hissing sounds were characterized by high frequencies (5000–10 000 Hz), both vipers and viperine snake hissing sounds were dominated by low frequencies (200–400 Hz). A principal component analysis revealed no overlap between grass snakes and vipers, but important overlaps between viperine snakes and vipers, and between viperine snakes and grass snakes. The likelihood that these overlaps respectively reflect natural selection for Batesian mimicry and phylogeny constraints is discussed. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 1107–1114.