03 March, 2020

Super toad eats one of the world's most venomous scorpion for dinner

Tityus serrulatus Lutz & Mello, 1922 (Buthidae) is one of the world's most venomous scorpions and a public health problem in parts of Brazil. This is an invasive species that has spread to many regions and are also found in urban habitats increasing the probability of human interactions.

Help reducing the populations of this potent species can be found in unusual places. Carlos Jared and co-workers have recently publish an article showing that the “cururu toads” Rhinella icterica (Spix, 1824) capture and eat the deadly Tityus species with great appetite. In addition, the toad seems resistant to the venom of Tityus serrulatus. A group of toads were injected with both letal dose and five-time lethal dose of venom (for mice), but none of the toads died or showed any effects of the venom. Quite a super-toad!

So keeping the toads in your garden or vicinity may be a helpful tool in the biological control of this dangerous scorpion in Brazil.

In recent years, SE Brazil, the most populous region in the country with an estimated population of 88 million, has been experiencing an alarming increase in scorpions accidents (scorpionism), mainly caused by the yellow scorpion (Tityus serrulatus), or “escorpi~ao amarelo” in Portuguese. This species is considered particularly dangerous to humans and can reproduce by parthenogenesis favouring rapid dispersal and colonization of new environments. Since the 1940s, owing to the growing danger represented by scorpionism, public control policies have been developed, including active search for scorpions, together with the use of toxic substances applied in places most likely to serve as their refuges. Even so, the number of accidents is increasing year by year, presently at an alarming rate. It seems evident that the increase in accidents is directly (or primarily) related to the lack of predators that in healthy environmental conditions would naturally control scorpion populations. However, due to environmental changes, leading to a lack of predators, scorpions have been gradually invading the urban environment. Arachnids and insects in general, as well as some other invertebrates, are preyed upon by anuran amphibians (toads, frogs and tree frogs). Toads (family Bufonidae) are nocturnal, large, and highly voracious animals, capable of actively exploring extensive areas and consuming large numbers of insects and arachnids daily. One of the most common toad species in southeastern Brazil is Rhinella icterica. Both R. icterica and T. serrulatus inhabit the same nocturnal environment. The predatory action of toads, specifically on scorpions, is practically unknown from behavioural and toxinological points of view. Thus, we studied the predatory behaviour of this toad against the yellow scorpion and evaluated the resistance of the amphibian to scorpion venom. Our results show that R. icterica is a voracious predator of T. serrulatus and is extremely resistant to its venom. Human/toad relationship throughout western history has always been very conflicted and possibly one of the factors that most has contributed to human ignorance of the role of these amphibians in maintaining ecological balance. Presently, the control of scorpionism is being performed through active search and/or the use of chemical agents, although showing little efficacy in reducing human accidents. In the medium or long term, more effective actions taking into account the biology of scorpions and their predators have never been taken to reduce these accidents.

Jared C, Alexandre C, Mailho-Fontana PL, Pimenta DC, Brodie ED, Jr., Antoniazzi MM. Toads prey upon scorpions and are resistant to their venom: A biological and ecological approach to scorpionism. Toxicon. 2020;178:4-7.[Subscription required for full text]

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