Tag Archives: predation

Snails as snake prey

Several snake species are known to prey on molluscs, and in the Neotropics some examples are already known; e.g., in the recent book on Belizan land snails by Dourson et al. pictures are given of Sibon species consuming a Drymaeus.

By serendipity I found a paper by Sazima & Muscat (2016) on Dipsas snakes in Brazil, which are known to feed on snails and slugs. The first author had reported in the past about the challenges that these molluscs offer to their predator. Snails must be removed from their shell and slugs release plenty of mucus, making snail handling time-consuming and handling slugs poses the risk of sticking to the substratum. Most observations are based on laboratory conditions, but this paper describes how newly hatched snakes are feeding on snails under natural conditions.

Schermafbeelding 2019-04-09 om 09.22.03

The (unwilling) victims in these cases were respectively Bulimulus tenuissimus (d’Orbigny, 1835) and Helicina angulata G.B. Sowerby, 1873. Both observations were made in Sao Paulo state in different forests.

Reference:
Sazima, I. & Muscat, E., 2016. Shelled baby food: Newly hatched goo‐eating snakes of the genus Dipsas (Squamata: Dipsadidae) prey on snails in nature. – Herpetologia Brasileira, 5 (3): 63-64. 

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Predation by fireflies

Sometimes one need to consult obscure papers in related disciplines to find some data on predation of molluscs. Recently a paper was published by Madruga (2018), reporting “a multiple-choice feeding-preference experiment was made to test the feeding behaviour of the larvae of Alecton discoidalis Laporte, 1833, a Cuban endemic firefly. It was found that in 60% of cases the larvae preferred to feed on Praticolella griseola (Pfeiffer, 1841), an introduced species of snail, considered a farming pest. Therefore, these lampyrid larvae seem to be a natural predator of this snail, which could be considered as a biological agent for pest control of the snail”.

As this paper was not readily available to me, I searched for it and by serendipity found an older one with additional data (Madruga & Hernández, 2010): “Alecton Laporte, 1833, with four known species is the only firefly genus endemic to Cuba. Alecton discoidalis Laporte, 1833, is its most common species, distributed in the western half of the country. Unfortunately, much of its life history remains unknown, as with the rest of Cuban representatives of the family Lampyridae. Larvae are associated with adults of A. discoidalis through rearing, and observations on larval feeding habits of this species are presented. Thirteen species belonging to seven gastropod families are reported for the first time as prey of A. discoidalis larvae. Our data suggest that these are generalist predators of terrestrial snails. A remarkably close association exists between this lampyrid and operculate species of snails. The later represents the most abundant and diverse group of molluscs in limestone landscapes, where the beetles are commonly found”.

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References:
Madruga, O., 2018. Seleccion alimentaria de las larvas de la luciernaga cubana Alecton
discoidalis (Coleoptera: Lampyridae). – Boletin de la Sociedad Entomológica Aragonesa, 62: 321-322.
Madruga, O. & Hernández, M., 2010. Larval Feeding Habits of the Cuban Endemic Firefly Alecton discoidalis Laporte (Coleoptera: Lampyridae). – Psyche (2010): e149879 (5 pp.).

 

Physical defense strategies

Predators play of course an important role in the ecology of snails, and various groups have developed their own strategy during the evolutionary process to try to fence off their enemies. Simone just published an overview of these strategies in South American land snails in a new (privately run) digital journal, which he called ‘Malacopedia’.

Unfortunately, the website of the journal seems out of order, so I cannot provide a direct link to the paper.

In his paper he discusses apertural barriers, changes in the direction of shell growth, hyper-coiling of the shell, hyper-retraction of the animal, alterations of size, and sinistral coiling.

This review seems to me a useful start, as the topic has been treated in literature mainly regarding marine and freshwater species. The ecology, biology and life cycle aspects of land snails have received comparatively little attention, and further studies on this topic may be interesting. Especially when they are not limited to the Neotropical realm only.

Reference:
Simone, L.R.L., 2018. Physical defence strategies of South American land snails. – Malacopedia, 1: 3-11.

Predation by land planarians

Land planarians are increasingly been reported as predators of land snails, and several reports have been summarised by Cseh et al. (2017), as well as presenting new data.

“The food preference of Obama anthropophila Amaral, Leal-Zanchet & Carbayo, 2015, a species that seems to be spreading across Brazil’s human-modified environments, was investigated. Extensive experiments led to the conclusion that the generalized diet of this species may have facilitated its dispersal. The analysis of 132 feeding records of 44 geoplaninid species revealed a tendency for closely related species to feed on individuals from similar taxonomic groups, suggesting that in this group behavioral evolution is more conserved than phylogenetic diversification”.

The paper supplies a table with the known prey animals of land planarians.

Reference:
Cseh, A. et al., 2017. Observations on food preference of Neotropical land planarians (Platyhelminthes), with emphasis on Obama anthropophila, and their phylogenetic diversification. – Zoologia (Curitiba), 34:e12622

Land planarians and their snail prey

Land planarians are invertebrate predators having a high specues tichness in the Neotropics, e.g. in the Atlantic Forest ecoregion in Brazil (Boll & Leal-Zanchet, 2016). This recent study brought more details on the food preference of this group.

“Land planarians are recognized as important predators, yet studies on their feeding habits are usually restricted to invasive species. Thus, it is difficult to determine the real ecological role of this group in ecosystems and how their communities are structured. In the present study, we analyzed the diet of six co-occurring Neotropical land planarians and their success in capturing prey, based on experiments in the laboratory, in order to determine how they share resources in the same environment. We also calculated indices of food niche breadth and food niche overlap for land planarians for the first time. The diet of Luteostriata abundans comprises only woodlice and the diets of Obama ficki and Obama ladislavii are composed only of gastropods, while Paraba multicolor and Obama anthropophila feed on both gastropods and other land planarians. An invasive species recently found in Western Europe, Obama nungara, showed the highest food niche breadth, feeding on gastropods, earthworms and planarians. We found the highest niche overlap between O. anthropophila and P. multicolor. The results suggest that land planarians are frequent predators of woodlice and land gastropods in the Neotropical ecozone and thus are important for the maintenance of native ecosystems and for the control of invasive species. The coexistence of several species in the same habitat is possible due to the use of different species as main prey, which reduces interspecific competition”.

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Since the experiments were done in the laboratory, the authors had control on the prey species they offered to the planarians. For gastropods these were: Bradybaena similaris, Helix aspersa, Deroceras laeve, Sarasinula plebeia, and Belocaulus sp. These are all medium-sized species; it would be interesting to know if the planiarians also are predators of the larger sized species occurring in the region (Strophocheilidae, Megaspiridae), and to what extent they are a threat to endangered, native species in the Atlantic Forest.

Reference:
Boll, P.K. & Leal-Zanchet, A.M., 2016. Preference for different prey allows the coexistence of several land planarians in areas of the Atlantic Forest. – Zoology 119: 162–168.

Photo of the day (154): predating

Actually this is not a photo post, but linking to a video. And moreover, strictly speaking not about Neotropical snails; consider it one of my “malacological tidbits”.

154_Predating

The link is here, and shows research done in Singapore how a predatory flatworm ingests land snails. In contrast to some other predators this worm succeed in leaving no signs. An intact shell is all he leaves, so one has to be lucky to catch the two in their act (although I definitely have the impression this movie was made under controlled circumstances).

It might be interesting to observe in the field on predation of Neotropical snails too, since such ecological details are very scarce and data are scanty.

Many thanks to Liew Thor Seng for distributing this among colleagues.