Effects of chemical context on shell investigation behavior in hermit crabs

Specific chemicals in the environment evoke significant changes in the behavior of many aquatic organisms. We studied in the laboratory whether satiated individuals of the hermit crab, Pagurus longicarpus Say 1817, adjust their investigatory behavior towards an empty, optimal gastropod shell according to differences of chemical context. We also explored to what extent shell investigation by a crab in the same hunger state was affected by occupying an inadequately sized shell. Our results confirmed in part previous findings that crabs can discriminate the odor of freshly dead snails from the odor of freshly dead conspecifics. In the presence of the former odor, crabs inhabiting shells of inadequate size were more responsive and active than those in better-fitting shells. To the contrary, regardless of the quality of the inhabited shell, P. longicarpus remained practically motionless when presented with the odor of freshly dead conspecifics, possibly because the risks of incurring in predators would outweigh the benefits of acquiring a new shell. Unexpectedly, we found that crabs in both types of shell quality exhibited nearly the same behavior in control water, while crabs in adequate shells were more responsive in the presence of food odor. Individuals appeared insensitive to the odor of live snails; indeed, only one hermit crab species has been seen removing living snails from their shells. An intriguing result was that water conditioned by the odors of live conspecifics exerted a strong effect on all the individuals by inducing an intense shell investigation. Our study underlines the central role exerted by chemical detection in hermit crabs' behavior and demonstrates the existence of a complex interplay among chemical context, the physiological state of the animal, and the ecological pressures of the habitat.     

Interference and exploitation components in interespecific competition between sympatric intertidal hermit crabs

This study was designed to evaluate the effect of interference and exploitation competition in shell partitioning between two hermit crab species (Pagurus criniticornis and Clibanarius antillensis). Field samples revealed that shells of the gastropod Cerithium atratum were the main resource used by both hermit crab species and that Pagurus used eroded or damaged shells in higher frequency than Clibanarius. The exploitative ability of each species was compared between species in the laboratory using dead gastropod (Cerithium) baits to simulate predation events and signalize newly available shells to hermit crabs. Pagurus reached the baits more rapidly than Clibanarius, but this higher exploitative ability did not explain shell utilization patterns in nature. Another experiment evaluated the dominance hierarchy between these two hermit crab species and revealed that Clibanarius was able to outcompete Pagurus for higher quality shells in agonistic encounters. This higher interference competitive ability of Clibanarius in relation to Pagurus may explain field observations. Nevertheless, Pagurus may be responsible to enhance shell availability to other hermit crab species that have lower ability to find and use newly available shells. Differently, the poorer condition of shells used by Pagurus, the higher ability of this species to attend gastropod predation events and its higher consumption rate by shell-breaking crabs (Menippe nodifrons) may increase its predation risks, thus revealing the disadvantages of such an exploitative competitive strategy for hermit crabs.     

Ecological relations between hermit crabs and their shell-supplying gastropods: Constrained consumers

Hermit crabs are critically dependent upon gastropod shells for their survival and reproductive fitness. While anecdotal reports have suggested that hermit crabs may be capable of removing live gastropods from their shells to access the essential shell resource, no systematic experiments have been conducted to investigate this possibility. This paper reports experiments on both marine (Pagurus bernhardus) and terrestrial (Coenobita compressus) hermit crabs in which crabs were paired in the laboratory with the gastropods whose shells they inhabit in the field. Pairings included both shelled and naked crabs and spanned the full range of the gastropod life cycle. Neither marine nor terrestrial hermit crabs were successful at removing live gastropods from their shells. Furthermore, only a small fraction of the crabs (5.7%) were capable of accessing shells in which the gastropod had been killed in advance, with its body left intact inside the shell. Finally, although hermit crabs readily entered empty shells positioned on the surface, few crabs (14.3%) were able to access empty shells that were buried just centimeters beneath them. These results suggest that hermit crabs are constrained consumers, with the shells they seek only being accessible during a narrow time window, which begins following natural gastropod death and bodily decomposition and which typically ends when the gastropod's remnant shell has been buried by tidal forces. Further experiments are needed on more species of hermit crabs as well as fine-grained measurements of (i) the mechanical force required to pull a gastropod body from its shell and (ii) the maximum corresponding force that can be generated by different hermit crab species' chelipeds.     

Avoidance of drilled gastropod shells by the hermit crab Pagurus longicarpus at Nahant, Massachusetts

Most hermit crabs depend on empty gastropod shells for shelter; competition for appropriate shells is often severe. This study determined whether shells that have been drilled by naticid gastropods are suitable for occupancy by the hermit crab Pagurus longicarpus. Differences in the characteristics of empty shells and those occupied by hermit crabs were assessed at two adjacent field sites in Nahant, Massachusetts. Drilling damage was far more frequent in empty gastropod shells than in shells occupied by hermit crabs, suggesting that individuals of P. longicarpus avoid drilled shells. They did not appear to avoid shells with other forms of damage. Laboratory experiments confirmed that these hermit crabs preferentially chose intact shells over drilled shells, even when the intact shells offered were most suitable for crabs half the weight of those tested. Final shell choices were generally made within 1 h. The hermit crabs apparently discriminated between intact and drilled shells based on tactile cues, since crabs kept in the dark showed the same preference for intact shells. The hermit crabs strongly avoided, to nearly the same extent, artificially drilled shells, naturally drilled shells, and shells with holes artificially drilled on the opposite side of the shell from where they would normally be located. Possible selective forces causing P. longicarpus to show such strong behavioral avoidance of drilled shells include increased vulnerability of crabs in drilled shells to osmotic stress, predation, and eviction by conspecifics.     

Land hermit crabs use odors of dead conspecifics to locate shells

A series of experiments at two tropical locations tested the ability of land hermit crabs Coenobita perlatus (H. Milne Edwards) and Coenobita compressas (H. Milne Edwards) to detect and respond to odors of dead conspecifics. An attraction array compared numbers of crabs attending hidden food odors and dead conspecific odors. Pit experiments tested crab shell-acquisition behaviors at different hidden odors. Bucket experiments confined crabs collected from various categories (feeding crabs, wandering crabs and crabs aggregated at dead conspecific odors) and tested behavioral responses to odors and an empty shell. Land hermit crab behavior at both sites was similar. Crabs were attracted to dead conspecific odors up to 10 times more than to food odors. Crabs attracted to dead conspecifics displayed significantly more shell-acquisition behaviors: touching other crab's shells in an exploratory manner and switching shells if an empty shell was available. In buckets, crabs from each category switched into shells. Results are compared to previous reports of similar shell-seeking behaviors by marine hermit crabs in response to dead conspecific odors. It is suggested that responding to dead conspecific odors for shell source location is an evolutionarily conserved behavior developed before hermit crabs became terrestrial.     

Gastropod shells: A dynamic resource that helps shape benthic community structure

Empty gastropod shells are an important resource for many animals in shallow benthic marine communities. Shells provide shelter for hermit crabs, octopuses, and fishes, provide attachment substratum for hermit crab symbionts, and directly or indirectly modify hermit crab predation. Creation of an empty shell due to predation of one gastropod on another and acquisition of that shell by a hermit crab are two key events in the subsequent use of that shell. Shells of different gastropod species and the species of hermit crab acquiring them affect the symbiont complement that attaches to the shell, which in turn may affect future shell use by other symbionts. Certain shell types worn by the hermit crab, Pagurus pollicaris Say, are positively associated with the symbiotic sea anemone, Calliactis tricolor (Lesueur), which protects the hermit crab from predation by the crab, Calappa flammea (Herbst), and possibly from the octopus, Octopus joubini Robson. Shells of other species of gastropods are resistant to being crushed by the spiny lobster, Panulirusargus (Latreille). The inter-and intraspecific interactions centered on the gastropod shell are termed a “habitat web.” The potential of the shell to limit the size and distribution of animal populations demonstrates how this resource helps shape community structure.     

What makes a good home for hermits? Assessing gastropod shell density and relative strength

The survival and reproductive success of hermit crabs is intrinsically linked to the quality of their domicile shells. Because damaged or eroded shells can result in greater predation, evaluating shell structure may aid our understanding of population dynamics. We assessed the structural attributes of Cerithium atratum shells through assessments of (a) density using a novel approach involving computed tomography and (b) tolerance to compressive force. Our goal was to investigate factors that may influence decision making in hermit crabs, specifically those that balance the degree of protection afforded by a shell (i.e. density and strength) with the energetic costs of carrying such resources. We compared the density and relative strength (i.e. using compression tests) of shells inhabited by live gastropods, hermit crabs (Pagurus criniticornis) and those found empty in the environment. Results failed to show any relationship between density and shell size, but there was a notable effect of shell density among treatment groups (gastropod/empty/hermit crab). There was also a predictable effect of shell size on maximum compressive force, which was consistent among occupants. Our results suggest that hermit crabs integrate multiple sources of information, selecting homes that while less dense (i.e. reducing the energy costs of carrying these resources), still offer sufficient resistance to compressive forces (e.g. such as those inflicted by shell-breaking predators). Lastly, we show that shell size generally reflects shell strength, thus explaining the motivation of hermit crabs to search for and indeed fight over the larger homes.     

Land hermit crab (Coenobita clypeatus) densities and patterns of gastropod shell use on small Bahamian islands

Aim To examine patterns of abundance, density, size and shell use in land hermit crabs, Coenobita clypeatus (Herbst), occurring on three groups of small islands, and to determine how these variables change among islands. Location Small islands in the Central Exuma Cays and near Great Exuma, Bahamas. Methods Land hermit crabs were captured in baited pitfall traps and were separately attracted to baits. A mark–recapture technique was used in conjunction with some pitfall traps monitored for three consecutive days. The size of each crab and the type of adopted gastropod shell were recorded, along with physical island variables such as total island area, vegetated area, island perimeter, elevation and distance to the nearest mainland island. Results Relative abundances, densities and sizes of crabs differed significantly among the three island groups. Densities of land hermit crabs were as high as 46 m⁻² of vegetated island area. In simple and multiple linear regressions, the only variable that was a significant predictor of the abundance of hermit crabs was the perimeter to area ratio of the island. Patterns of gastropod shell use varied significantly among the island groups, and the vast majority of adopted shells originated from gastropod species that inhabit the high intertidal and supratidal shorelines of the islands. Main conclusions Although densities of land hermit crabs varied, they were relatively high on many islands, and land hermit crabs may play an important role in these insular food webs. Patterns of shell use may be strongly restricted by island geomorphology: irregular shorelines provide relatively more habitat for the gastropod species that account for the majority of adopted shells and the steep sides of the islands prevent the accumulation of marine gastropod shells. The size of adult hermit crabs appears to be limited by the relatively small gastropod shells available, while the abundance of hermit crabs may be limited by the number of shells available.     

Symbiosis of sea anemones and hermit crabs: different resource utilization patterns in the Aegean Sea

The small-scale distribution and resource utilization patterns of hermit crabs living in symbiosis with sea anemones were investigated in the Aegean Sea. Four hermit crab species, occupying shells of nine gastropod species, were found in symbiosis with the sea anemone Calliactis parasitica. Shell resource utilization patterns varied among hermit crabs, with Dardanus species utilizing a wide variety of shells. The size structure of hermit crab populations also affected shell resource utilization, with small-sized individuals inhabiting a larger variety of shells. Sea anemone utilization patterns varied both among hermit crab species and among residence shells, with larger crabs and shells hosting an increased abundance and biomass of C. parasitica. The examined biometric relationships suggested that small-sized crabs carry, proportionally to their weight, heavier shells and increased anemone biomass than larger ones. Exceptions to the above patterns are related either to local resource availability or to other environmental factors.     

Effect of gastropod shell characteristics and hermit crabs on shell Epifauna

The epifauna on gastropod shells occupied by the hermit crabs Pagurus pollicaris (Say) and P. longicarpus (Say) was examined, as was the utilization of shells by these two hermit crabs. In the study area in Tampa Bay, Florida, shells were not a limiting factor to the hermit crab population, and there apparently was little competition for shells. Interspecific competition for shells was limited because the two hermit crab species differed in size and hence occupied shells of different sizes. The total number and density of most epifaunal species were higher on shells occupied by hermit crabs than on unoccupied shells, possibly because hermit crabs prevent their shells from being buried and hence lengthen the time the epifaunal community can grow and develop. The hermit crab species also appeared to affect the epifaunal community, for the total number and density of most epifaunal species were larger on shells occupied by P. pollicaris than P. longicarpus. With increasing shell size, the populations of most epifaunal species, also were larger but not their density. Least influential in affecting the epifaunal community was the species of shells.     

Shell occupancy of the intertidal hermit crab Clibanarius erythropus (Decapoda,Diogenidae) on São Miguel (Azores)

The intertidal hermit crab Clibanarius erythropus was collected at three sites on São Miguel (Azores) during low spring tides. Shells occupied were identified and measured. Crab sizes ranged from 1.78 to 13.67 mm (cephalothoracic shield length), with an average size of 4.40 ± 1.44 mm. Of the 19 different shells utilised, the most frequent were Littorina striata (23.8%), Nassarius incrassatus (22.5%) and Mitra sp. (22.0%). At Fenais da Luz, L. striata was most frequently occupied, while at Água de Alto it was N. incrassatus and, at Caloura, Mitra sp. shells were most frequently used. Shell selection appears to be determined by respective sizes of hermit crab and shell species. Small size-class crabs occupy more shell species than larger crabs. The smallest crab was found at Fenais da Luz occupying a small Bittium sp., whereas the largest crab was found at Caloura inhabiting Stramonita haemastoma.     

Are the preference and selection patterns of hermit crabs for gastropod shells species- or site-specific?

Experimental analyses of hermit crabs and their preferences for shells are essential to understand the intrinsic relationship of the crabs' dependence on shells, and may be useful to explain their shell use pattern in nature. The aim of this study was to evaluate the effect of crab species and site on the pattern of shell use, selection, and preference in the south-western Atlantic hermit crabs Pagurus brevidactylus and Pagurus criniticornis, comparing sympatric and allopatric populations. Differently from the traditional approach to evaluate shell preference by simply determining the shell selection pattern (i.e., the number of shells of each type selected), preference was defined (according to [Liszka, D., Underwood, A.J., 1990. An experimental design to determine preferences for gastropod shells by a hermit-crab. J. Exp. Mar. Biol. Ecol., 137(1), 47–62]) by the comparison of the number of crabs changing for a particular shell type when three options were given (Cerithium atratum, Morula nodulosa, and Tegula viridula) with the number of crabs changing for this same type when only this type was offered. The effect of crab species was tested at Cabelo Gordo Beach, where P. brevidactylus was found occupying shells of C. atratum, M. nodulosa, and T. viridula in similar frequencies, whereas P. criniticornis occupied predominantly shells of C. atratum. In laboratory experiments the selection patterns of the two hermit-crab species for these three gastropods were different, with P. criniticornis selecting mainly shells of C. atratum, and P. brevidactylus selecting more shells of M. nodulosa. The shell preference was also dependent on crab species, with P. criniticornis showing a clear preference for shells of C. atratum, whereas P. brevidactylus did not show a preference for any of the tested shells. The effect of site was tested for the two species comparing data from Cabelo Gordo to Preta (P. brevidactylus) and Araçá beaches (P. criniticornis). The pattern of shell use, selection, and preference was demonstrated to be dependent on site only for P. brevidactylus. The results also showed that the shell use pattern of P. criniticornis can be explained by its preference at both sites, whereas for P. brevidactylus it occurred only at Cabelo Gordo, where the absence of preference was correlated with the similar use of the three gastropod species studied. Finally, the results showed that the shell selection pattern cannot be considered as a measure of shell preference, since it overestimates crab selectivity.     

Shell preference and utilization patterns in littoral hermit crabs of the bay of Panama

Shell utilization patterns of three sympatric hermit crab species from the Bay of Panama are examined. Shell preferences, as shown by laboratory choice experiments and the selective use of empty shells experimentally added to hermit crab populations, are shown to be important determinants of shell utilization under natural conditions.Factors which influence the types and sizes of shells occupied by hermit crabs in separate populations include: (1) the presence and relative abundance of different gastropod species; (2) the specific shell preferences of different hermit crab species; and (3) the presence and relative abundance of sympatric hermit crab competitors for the limited supply of empty shells. Since the size and type of shell occupied by a hermit crab influences its growth rate and reproductive output, these factors appear to have a direct effect on hermit crab fitness and the demographic structure of separate hermit crab populations.     

Shell selection behaviour and spatial distribution of three species of intertidal hermit crabs from Hormuz Island,Persian Gulf (Crustacea: Paguroidea)

Shell selection behaviour and spatial distribution of three hermit crab species, Diogenes avarus, D. karwarensis, and Areopaguristes perspicax, were studied at six sites along the intertidal zones of Hormuz Island in the Persian Gulf. 1025 specimens were collected occupying altogether 31 shell species (D. avarus 28 species, A. perspicax 22 species, and D. karwarensis 8 species). Diogenes avarus was found to be by far the most abundant of these three crab species, and Cerithidea cingulata the dominant shell occupied by these hermit crabs. The distribution of the hermit crabs significantly varied (p<0.05) among the sites. The number and the wide diversity of shells occupied in different sites show that the main factor in shell selection for these hermit crabs is the abundance and distribution of shell species in the field.     

Intraspecific competition and aggression for shells in the hermit crab Pagurus samuel1s

Many studies have investigated shell‐related behaviour in hermit crabs. Few studies, however, have focused specifically on the intraspecies aggression associated with shell competition. We examined intraspecies aggression in hermit crab (Pagurus samuelis) pairs as it relates to competition for a limiting resource, gastropod shells. Pairs of hermit crabs were observed in the laboratory in four different treatments that varied the presence or absence of shells for one or both of the crabs. Measurements of the latency to respond, the number of bouts, and the fight durations were recorded. There was a significant difference among treatments for all three measurements, and naked hermit crabs were much more aggressive than housed hermit crabs. There was no significant difference in aggression between males and females in any of the three treatments. The heightened aggression observed in naked P. samuelis is likely in service of acquiring a protective shell.     

MORPHOLOGY AND BEHAVIOR OF CRABS AND GASTROPODS FROM LAKE TANGANYIKA,AFRICA: IMPLICATIONS FOR LACUSTRINE PREDATOR-PREY COEVOLUTION

The shells of most lacustrine gastropods are typically small, weakly calcified, and modestly ornamented to unornamented. Similarly, most lacustrine crabs are usually small detritivores with weak chelae. A number of invertebrate taxa in Lake Tanganyika, however, deviate from these generalities. This study explores a predator-prey coevolution model as an explanation for the large, heavily calcified, and ornate gastropods and the robust, durophagous crabs of Lake Tanganyika. The endemic thiarid and viviparid gastropods from Lake Tanganyika have significantly thicker shells and higher frequencies of terminal apertural lip thickening than closely related cosmopolitan taxa from outside the lake. Tanganyikan gastropods also display considerably higher incidence of shell repair, following nonlethal shell damage, than cosmopolitan taxa of the same families. There is a strong positive correlation between gastropod apertural lip thickness and shell repair frequency among all the gastropod species analyzed. The endemic Tanganyikan potamonautid crab Platytelphusa armata (a molluscivore) possesses larger, more robust crushing chelae than other African potamonautid or potamonid crabs. In contrast with the cosmopolitan African crabs, the Tanganyikan crabs display molariform, rather than serrate dentition on their crushing chelipeds. In shell-crushing experiments, the Tanganyikan gastropod shells were an order of magnitude stronger than typical lacustrine gastropod shells, many well within the range of tropical marine gastropod shell strengths. Predation experiments with the endemic gastropods Spekia, Neothauma, Lavigeria spp., Paramelania spp. and the crab Platytelphusa armata showed that increased size, apertural lip thickness or shell sculpture reduced the successful predation rate of P. armata. Crabs with large chelae have a greater ratio of successful: unsuccessful attacks than crabs with small chelae. Among cases of successful predation, crabs with large chelae employed predation methods that required less time and energy (such as crushing the shell in the cheliped) than the methods employed by crabs with small chelae (such as peeling the shell from the aperture or the spire). The morphological, shell-crushing, and aquarium experiment data, considered in concert, provide strong support for the idea that the endemic gastropods and crabs of Lake Tanganyika have coevolved over the past 7 million years.     

Shelter association between the hermit crab Sympagurus dimorphus and the zoanthid Epizoanthus paguricola in the southwestern Atlantic Ocean

Schejter, L. and Mantelatto, F.L. 2011. Shelter association between the hermit crab Sympagurus dimorphus and the zoanthid Epizoanthus paguricola in the southwestern Atlantic Ocean. —Acta Zoologica (Stockholm) 92 : 141–149. The available literature on zoanthid–hermit crab associations deals only with records of this phenomenon, providing no detailed information. We describe, for the first time, the shell‐like colonies of Epizoanthus paguricola associated with the hermit crab Sympagurus dimorphus from benthic samples taken in the Argentine Sea, between 85 and 131 m depth, and provide information about morphometric relationships between the hermits and the zoanthids. In total, 260 specimens (137 males and 123 females) of S. dimorphus were collected, 240 (92.3%) of which were living in symbiosis with E. paguricola. The remaining 20 (7.7%) were living inside gastropod shells. As the initial structure of the pseudoshell, 12 different gastropod species were found (all were almost totally covered with colonies of E. paguricola). The hermit crab lives in the spiral cavity inside the soft colony, which seemed to be slightly different depending on the initial gastropod. Aperture pseudoshell morphology did not seem to be related to the sex of the hermit crab host, although males showed larger apertures for a given colony size. This fact is probably related to a larger size of male’s cheliped (sexual dimorphic character) used like a gastropod operculum and that may serve as a template for the growing of the aperture pseudoshell edge. The number of epizoanthid polyps per colony increased in relation to the weight of the colony and to the size of the hermit crab. A process of selection of the initial shell was evident, because species of Naticidae were not the most common gastropods in this benthic community, but were those most used by hermit crabs (>60%). The puzzling association between hermit crab, shell and zoanthid presumably occurs during the hermit juvenile phase, when the crab occupies a small shell, and a zoanthid larva settles on it. Given the close relationship between S. dimorphus and E. paguricola found in this region, we support the idea that due to the low availability of adequate gastropod shells for hermit life cycle, this association allows the establishment and the continuity of the hermit crab population in the studied area.     

Antipredator defence of the hermit crab Pagurus filholi induced by predatory crabs

Hermit crabs have two antipredator tactics: taking refuge in its shell and fleeing. We examined the following two hypotheses using the hermit crab Pagurus filholi : (1) hermit crabs change their preference for shell types that they take refuge in and/or change the timing of fleeing (i.e. the duration of refuge in the shell) when they perceive a predator threat; (2) the type of shell that a hermit crab occupies affects the fleeing tactic of the individual. Under the stimulus of a crushed conspecific, hermit crabs changed neither their preference for shell species nor their refuge duration. On the other hand, under the stimulus of the predatory crab Gaetice depressus , hermit crabs increased their preference for Batillaria cumingi shells, which provide superior protection against predators, and shortened their refuge duration in the shells even when they occupied those effective against predation. Refuge duration was longer in B. cumingi shells than in the more vulnerable shells of Homalopoma sangarense . These results suggest that both antipredator defences (changing shell and timing of fleeing) are induced by the stimulus of a predator, and the timing of fleeing is affected by the shell type occupied.     

Protection of the hermit crab Pagurus pollicaris say from predators by hydroid-colonized shells

Only one study has shown that a hydroid-colonized gastropod shell was a deterrent to predation on hermit crabs. In the present study, the hydroid-colonized shell protected the hermit crab Paguruspollicaris Say from the shell-crushing stone crab Menippe mercenaria (Say) and the non-shell-crushing octopus Octopus joubini Robson. The shell-crushing calico crab Hepatus epheliticus (Johansson) was not deterred, however, by a hydroid-colonized shell.     

Predator discrimination in the hermit crab Calcinus californiensis: tight for shell breakers,loose for shell peelers

Prey exposed to predators with different hunting and feeding modes are under different selective pressures, therefore it is expected that they should exhibit plastic and adaptive antipredator responses according to current risks. The hermit crab Calcinus californiensis faces two contrasting predators, the shell peeler Arenaeus mexicanus that hunts by active searching and the shell breaker Eriphia squamata that hunts by ambush. In order to discover whether C. californiensis displays plastic responses depending on the type of predatory challenge, we examined the shell size preference, the hiding time, and the escape velocity of hermit crabs in the presence of chemical cues from a shell peeler, a shell breaker, and a control. We also examined the role of shell fit on the escape velocity of the hermit crabs in natural tidal pools. Crabs chose shells with a loose fit (relatively large shells) in the presence of chemical cues from the shell peeler Arenaeus and shells with a tight fit when exposed to cues from the shell breaker Eriphia. The hermit crabs hid for shorter times and moved away faster from Eriphia than from Arenaeus stimulus. The use of a tight shell favours faster movement away from the shell breaker (pre‐capture strategy), but prevents the crab retracting deeper inside the shell, increasing the risk of be eaten by the shell peeler once captured. Hence, the use of loose shells that protect the crab from the shell peeler hinders fast escape. This study shows specific and plastic antipredatory responses to contrasting predators, each bringing adaptive benefits at different levels of the predator sequence.