Necrophagy in cave environments: ecological pressure due to food scarcity? A case study of necrophagy by a harvestman Discocyrtanus canjinjim Carvalho & Kury, 2017 (Arachnida: Opiliones) preying on an Eidmanacris sp. (Orthoptera: Phalangopsidae) carcass

Abstract

Cave environments present stable abiotic conditions, including permanent darkness, high humidity, and mild temperatures, while biotic factors reflect simplified ecological networks and energy constraints. Cave invertebrates, primarily detritivores and generalists, demonstrate specific adaptations to these conditions. Predation and necrophagy are critical behaviors shaped by the cave's scarcity of food resources. In this study, we report a rare necrophagy event involving Discocyrtanus canjinjim Carvalho & Kury, 2017 (Arachnida: Opiliones) feeding on a deceased cricket (Eidmanacris sp.) (Orthoptera: Phalangopsidae) in the Ponte de Pedra I Cave, Brazil. This limestone cave features large entrances and supports an oligotrophic system. The event occurred in an aphotic zone, where the harvestman displayed no flee behavior despite external stimuli. The presence of other predatory arachnids suggests potential intra-guild competition. Opiliones in the Cerrado and Caatinga exhibit opportunistic carnivory, consuming various prey taxa, including insects and vertebrates. Necrophagy, intra-guild predation, and cannibalism are behaviors reported in subterranean populations due to limited food availability. Climate change and anthropogenic pressures, such as deforestation and mining, threaten the stability of cave environments. Observations like this contribute to understanding the ecological dynamics within caves, highlighting the importance of preserving these fragile ecosystems.

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Entomological Communicaons, 6, 2024: ec06038
doi: 10.37486/2675-1305.ec06038
e-ISSN: 2675-1305
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Necrophagy in cave environments: ecological pressure due to food
scarcity? A case study of necrophagy by a harvestman Discocyrtanus
canjinjim Carvalho & Kury, 2017 (Arachnida: Opiliones) preying on an
Eidmanacris sp. (Orthoptera: Phalangopsidae) carcass
Vinícius F. Sperandei1, Crisna M. Borges2, Marcel S. Araújo³
1Universidade de Rio Verde, Rio Verde, GO, Brazil. 2Opilião - Grupo de Estudos Espeleológicos, Contagem, MG, Brazil. 3Universidade
Federal de São Carlos, São Carlos, SP, Brazil.
Corresponding author: vinicius.sperandei@gmail.com
Edited by: Nikolas G. Cipola
Received: September 26, 2024. Accepted: December 18, 2024. Published: December 30, 2024.
Abstract. Cave environments present stable abioc condions, including permanent darkness, high humidity, and mild temperatures, while bioc
factors reect simplied ecological networks and energy constraints. Cave invertebrates, primarily detrivores and generalists, demonstrate
specic adaptaons to these condions. Predaon and necrophagy are crical behaviors shaped by the cave's scarcity of food resources. In this
study, we report a rare necrophagy event involving Discocyrtanus canjinjim Carvalho & Kury, 2017 (Arachnida: Opiliones) feeding on a deceased
cricket (Eidmanacris sp.) (Orthoptera: Phalangopsidae) in the Ponte de Pedra I Cave, Brazil. This limestone cave features large entrances and
supports an oligotrophic system. The event occurred in an aphoc zone, where the harvestman displayed no ee behavior despite external smuli.
The presence of other predatory arachnids suggests potenal intra-guild compeon. Opiliones in the Cerrado and Caanga exhibit opportunisc
carnivory, consuming various prey taxa, including insects and vertebrates. Necrophagy, intra-guild predaon, and cannibalism are behaviors
reported in subterranean populaons due to limited food availability. Climate change and anthropogenic pressures, such as deforestaon and
mining, threaten the stability of cave environments. Observaons like this contribute to understanding the ecological dynamics within caves,
highlighng the importance of preserving these fragile ecosystems.
Keywords: Brazil, cave ecology, invertebrate behavior, subterranean ecosystems.
The cave environment is a distinct element of the landscape,
characterized by its stable abiotic conditions, permanent absence
of light in deeper zones, high humidity near saturation, and mild
temperature with little variation (Culver & Pipan 2009; Tobin et al.
2013). Biotic conditions include simplified ecological networks, minimal
or no primary production within the system, and energy support from
the oligotrophic system facilitated by physical and biological agents
(Simon et al. 2007). Energy availability varies between caves and
is influenced by factors such as the size and number of entrances,
affecting the system's carrying capacity and connection to the surface
environment (Silva et al. 2011; Pellegrini et al. 2016).
Cave invertebrate communities are primarily composed of
detritivores or generalists (Ferreira & Martins 1999) that exhibit
adaptations and tolerances to various biotic and abiotic characteristics
of the epigean environment, acting as environmental filters. These
invertebrates also occupy specific niches within the caves that align
with their physiological and behavioral traits (Simões et al. 2015).
The study of ecological interactions and predation events
within caves aims to determine whether the conditions of the cave
environment, such as reduced food availability, lead to behaviors
considered rare or if they are opportunistic (Bernardi et al. 2010; Souza-
Silva & Ferreira 2014; Bernardi et al. 2020). Among the rare interactions
occurring under conditions of scarcity is necrophagy, which is defined
as a feeding strategy where organisms obtain energy from consuming
the organic matter of already deceased animals (Wilson & Wolkovich
2011). Few species rely on this strategy as their primary resource; most
are predators or consumers that adopt this behavior opportunistically
(Trujillo et al. 2021).
In this study, we report a novel event of a male of Discocyrtanus
canjinjim Carvalho & Kury, 2017 (Arachnida: Opiliones) preying
on a previously deceased cricket, Eidmanacris sp. (Orthoptera:
Phalangopsidae). The observation (Fig. 1) was made in the Ponte de
Pedra I Cave, located in the municipality of Montividiu, Goiás State,
in the central-western region of Brazil (Fig. 2). This limestone cave
features large entrances and is intersected by the substantial Verdão
river. The cave's formations extend laterally at higher levels above the
riverbed.
Figure 1. Discocyrtanus canjinjim preying on the jumping leg of Eidmanacris
sp. (Orthoptera: Phalangopsidae) in the aphotic zone of Ponte de Pedra Cave,
Montividiu, Goiás.
Ponte de Pedra Cave is located in a permanent preservation area
within a strictu sensu Cerrado matrix, featuring a tropical wet and
dry (Aw) climate according to the Köppen classification (Alvarez et al.
Scientific Note

Entomological Communicaons, 6, 2024: ec06038
2
2013), characterized by hot, rainy summers and mild, dry winters in
Montividiu, Goiás. The cave has many entrances (Fig. 3) to the epigeal
zone for terrestrial areas and also at the passage of the Verdão River,
in addition to a skylight. This characteristic indicates a mosaic of light
zones where the aphotic area is restricted to a small area at the bottom
of the cave. During the summer, the local population and tourists use
the cave on weekends and the surrounding area where there are
bathing areas and camping areas, which can cause stress to the local
fauna and deposition of anthropic material.
Figure 2. Location of Ponte de Pedra Cave in the state of Goiás, surrounded by
a Cerrado matrix, Brazil.
The event was observed for about five minutes without any
interference from the researchers, who did not collect the animals for
preservation. The harvestman was found in an aphotic zone on a lateral
wall approximately 1 meter above the floor where the Eidmanacris sp.
carcass, already dried after death, was located (identification to the
species level was not possible due to the state of decomposition).
Despite the researchers' approach and the presence of light from
their lanterns in the otherwise unlit area of the cave, the harvestman
remained motionless, holding onto its prey without attempting to flee.
The cave is divided into a large entrance hall with a continuous
body of water and fallen blocks, an upper hall with difficult access
and a sandy floor, a deeper conduit, where there are dysphotic and
aphotic zones and some narrow entrances between rocks where there
is the entry of floodwaters that bring with them plant material (leaves,
branches). Throughout the entire length of the cave, there is a lot of
humidity due to the presence of the river crossing the entire cavity and
the presence of epigean plant roots.
Other predatory arachnids, such as spiders of the genus Loxosceles
Heineken & Lowe, 1832 (Arachnida: Sicariidae) and amblypygids
Heterophrynus sp., among other species of spiders and harvestmen,
were found in the cave and near the necrophagy event site, indicating
potential intra-guild competition within this environmental niche.
In addition to the arachnids found and reported in this work,
lepidopterans, ants, termites, anurans, a small colony of bats, and
coleopterans were also found.
Crickets Eidmanacris sp. are not reported for aphotic areas of caves,
being normally abundant in the entrance or ecotonal areas between
the epigean and hypogean environments. In this case, other individuals
were sighted in the cave entrance area, which may indicate that there
was predation by another predator or that the carcass was taken to
this luminous zone by abiotic agents such as flooding, for example. Two
other individuals of D. canjinjim were also seen on side walls, both in
the dysphotic zone of the cave, apparently at rest, indicating that these
animals move between the luminous zones.
Opiliones are nocturnal arachnids inhabiting the Cerrado and
Caatinga, primarily in landscape niches such as caves, tree trunks,
under stones, or on vegetation (Curtis & Machado 2007; Giupponi
et al. 2017; Rubim et al. 2023). Their diet is characterized as
opportunistically carnivorous, with records of various taxa, including
Hymenoptera (Rubim et al. 2022), Lepidoptera, Hemiptera (Silva
A
D
B
E
C
F
Figure 3. A - Main entrance to the cave Ponte de Pedra; B - Main entrance hall, all in the photic zone of the cavity with a body of running water; C - Verdão River and
skylight; D - Very narrow secondary inlet with a lot of deposition of plant organic matter; E - Waterfall around the cave; F - Karst and Cerrado surrounding the cavity.

Sperandei et al. 2024
3
et al. 2024), crustaceans, and annelids (Sabino & Gnaspini 1999),
gastropods (Nyffeler & Symondson 2011) and even vertebrates like
frogs (Menegucci et al. 2020). Temperature range and humidity levels
serve as key environmental filters for these animals. Thus, more
stable environments, such as caves, are conducive to their habitation
(Bragagnolo et al. 2007).
Harvestmen of the genus Discocyrtanus Roewer, 1929 (Arachnida:
Opiliones) indicate diverse feeding habits and dependence on olfactory
cues from their prey via chemoreceptors, which can be live animals,
dead or decomposing animals, as well as fungi and plant material
(Costa & Willemart 2013; Nyffeler et al. 2023).
Necrophagy has been observed in top-predator arachnids in
Neotropical caves, including necrophagy events involving bats by whip-
spiders (Prous et al. 2017; Trujillo et al. 2021). Predation behaviors vary
when comparing populations of generalist animals in subterranean
and surface environments. The cave environment, characterized by
significantly lower food availability, often leads to broader utilization
of all potential prey, including dead prey (necrophagy), intra-guild
predation, and even cannibalism (Chapin 2015; Prous et al. 2017;
Bernardi et al. 2020).
It is important to note that stable environments are threatened
by climate change (Pereira et al. 2024) and cave environments by
anthropogenic pressures such as deforestation, degradation and
pollution of water bodies, lowering of the water table, and mining
activities (Van Beynen & Townsend 2005; Calò & Parise 2006;
Sperandei et al. 2023). Scientific records of observations like this
provide a foundation for ecological network studies, fostering a deeper
understanding of how subterranean environments are utilized by their
inhabitants.
Acknowledgments
The authors thank the owners of the Ponte de Pedra farm and
restaurant for preserving the cave and its surroundings and for allowing
access and research on their property.
Funding Information
No funding received.
Authors' Contribuitions
VFS: Conceptualization, Investigation, Resources, Supervision,
Writing - original draft; CMB: Investigation, Writing - review & editing;
MSA: Investigation, Writing - review & editing.
Conflict of Interest Statment
The authors declare no conflict of interest.
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