Pinching or stinging? Comparing prey capture among scorpions with contrasting morphologies

Background: Scorpions can use their pincers and/or stingers to subdue and immobilize their prey. A scorpion can thus choose between strategies involving force or venom, or both, depending on what is required to subdue its prey. Scorpions vary greatly in the size and strength of their pincers, and in the efficacy of their venom. Whether this variability is driven by their defensive or prey incapacitation functionis unknown. In this study, we test if scorpion species with different pincer morphologies and venom efficacies use these weapons differently during prey subjugation. To that end, we observed Opisthacanthus elatus and Chactas sp. with large pincers and Centruroides edwardsii and Tityus sp. with slender pincers. Methods: The scorpion pinch force was measured, and behavioral experiments were performed with hard and soft prey (Blaptica dubia and Acheta domesticus). Stinger use, sting frequency and immobilization time were measured. Results: We found that scorpions with large pincers such as O. elatus produce more force and use the stinger less, mostly subjugating prey by crushing them with the pincers. In C. edwardsii and Tityus sp. we found they use their slender and relatively weak pincers for holding the prey, but seem to predominantly use the stinger to subjugate them. On the other hand, Chactas sp. uses both strategies although it has a high pinch force. Conclusions: Our results show that scorpionspecies with massive pincers and high pinch force as O. elatus use the stinger less for prey subjugation than scorpionspecies with slenderpincers.(AU)

Linking toxicity and predation in a venomous arthropod: the case of Tityus fuhrmanni (Scorpiones: Buthidae), a generalist predator scorpion

Background: Scorpions are arachnids that have a generalist diet, which use venom to subdue their prey. The study of their trophic ecology and capture behavior is still limited compared to other organisms, and aspects such as trophic specialization in this group have been little explored. Methods: In order to determine the relationship between feeding behavior and venom toxicity in the scorpion species Tityus fuhrmanni, 33 specimens were offered prey with different morphologies and defense mechanisms: spiders, cockroaches and crickets. In each of the experiments we recorded the following aspects: acceptance rate, immobilization time and the number of capture attempts. The median lethal dose of T. fuhrmanni venom against the three different types of prey was also evaluated. Results: We found that this species does not have a marked difference in acceptance for any of the evaluated prey, but the number of capture attempts of spiders is higher when compared to the other types of prey. The immobilization time is shorter in spiders compared to other prey and the LD50 was higher for cockroaches. Conclusions: These results indicate that T. fuhrmanni is a scorpion with a generalist diet, has a venom with a different potency among prey and is capable of discriminating between prey types and employing distinct strategies to subdue them.(AU)

Linking toxicity and predation in a venomous arthropod: the case of Tityus fuhrmanni (Scorpiones: Buthidae), a generalist predator scorpion

Abstract Background: Scorpions are arachnids that have a generalist diet, which use venom to subdue their prey. The study of their trophic ecology and capture behavior is still limited compared to other organisms, and aspects such as trophic specialization in this group have been little explored. Methods: In order to determine the relationship between feeding behavior and venom toxicity in the scorpion species Tityus fuhrmanni, 33 specimens were offered prey with different morphologies and defense mechanisms: spiders, cockroaches and crickets. In each of the experiments we recorded the following aspects: acceptance rate, immobilization time and the number of capture attempts. The median lethal dose of T. fuhrmanni venom against the three different types of prey was also evaluated. Results: We found that this species does not have a marked difference in acceptance for any of the evaluated prey, but the number of capture attempts of spiders is higher when compared to the other types of prey. The immobilization time is shorter in spiders compared to other prey and the LD50 was higher for cockroaches. Conclusions: These results indicate that T. fuhrmanni is a scorpion with a generalist diet, has a venom with a different potency among prey and is capable of discriminating between prey types and employing distinct strategies to subdue them.

Assimetria e experiência no comportamento de tocar a presa de aranhas cuspideiras Scytodes globula Nicolet, 1849 (Araneae, Scytodidae) / Asymmetry and experience in the predatory probing behavior of spitting spiders Scytodes globula Nicolet, 1849 (Araneae, Scytodidae)

Pouco se conhece a respeito das assimetrias comportamentais em aranhas. Procuramos aqui verificar, em oito aranhas da espécie Scytodes globula, vieses laterais e efeitos de experiência nos movimentos de tocar a presa com as pernas I e II, durante quatro encontros predatórios sucessivos com aranhas-marrons Loxosceles intermedia. No primeiro encontro, as pernas esquerdas de ambos os pares foram usadas mais do que as pernas direitas; no último encontro, apenas as pernas I esquerdas. A frequência dos toques com as pernas I e II diminuiu do primeiro para o último encontro. Os resultados confirmam resultados anteriores sobre a lateralidade de S. globula e mostram a existência de efeitos de experiência no comportamento predatório desta aranha.(AU)

Little is known about behavioral asymmetries in spiders. We here examined lateral biases and experience effects in probing movements with legs I and II in eight spitting spiders Scytodes globula during four successive predatory encounters with recluse spiders Loxosceles intermedia. In trial 1, left leg probing was more frequent than right leg probing, for both pairs of legs; in the last trial, only for legs I. Frequency of probing by left and right legs of both pairs decreased from the first to the last trial. Results confirm previous ones on the laterality of S. globula and indicate that experience may influence the predatory behavior of this spider.(AU)

Assimetria e experiência no comportamento de tocar a presa de aranhas cuspideiras Scytodes globula Nicolet, 1849 (Araneae, Scytodidae) / Asymmetry and experience in the predatory probing behavior of spitting spiders Scytodes globula Nicolet, 1849 (Araneae, Scytodidae)

Pouco se conhece a respeito das assimetrias comportamentais em aranhas. Procuramos aqui verificar, em oito aranhas da espécie Scytodes globula, vieses laterais e efeitos de experiência nos movimentos de tocar a presa com as pernas I e II, durante quatro encontros predatórios sucessivos com aranhas-marrons Loxosceles intermedia. No primeiro encontro, as pernas esquerdas de ambos os pares foram usadas mais do que as pernas direitas; no último encontro, apenas as pernas I esquerdas. A frequência dos toques com as pernas I e II diminuiu do primeiro para o último encontro. Os resultados confirmam resultados anteriores sobre a lateralidade de S. globula e mostram a existência de efeitos de experiência no comportamento predatório desta aranha.

Little is known about behavioral asymmetries in spiders. We here examined lateral biases and experience effects in probing movements with legs I and II in eight spitting spiders Scytodes globula during four successive predatory encounters with recluse spiders Loxosceles intermedia. In trial 1, left leg probing was more frequent than right leg probing, for both pairs of legs; in the last trial, only for legs I. Frequency of probing by left and right legs of both pairs decreased from the first to the last trial. Results confirm previous ones on the laterality of S. globula and indicate that experience may influence the predatory behavior of this spider.

Comportamento de predação de podisus nigrispinus (dallas, 1851) (hemiptera: pentatomidae) em função da disponibilidade de alimento

ABSTRACT Predators with extraoral digestion may consider several factors to attack a prey item based not only on the nutritional value but also on the energy expended in prey handling (capture, digestion and ingestion of liquefied content). The predatory stinkbug may require a large amount of water to produce saliva and enzymes used to digest prey tissues and, hence, exhibit behavior related to the water source. Thus, this study investigated the behavioral choice of the predator between a moisture source (water and plant) and a prey item and weight gain by the predatory stinkbug Podisus nigrispinus (Dallas) (Hemiptera: Pentatomidae). Predator adults had free choice to feed between water and the pre-pupa of Alabama argillacea (Hübner, 1823) (Lepidoptera: Noctuidae) (i), between the host plant (cotton) and larvae of A. argillacea (ii), or on each of these food sources individually (iii). Although starved for 48h, P. nigrispinus exhibited a similar choice between feeding either on water or on prey, and preferred to feed on plants compared to prey when having access to prey and cotton plants simultaneously. Under the non-choice test, predators chose to feed on the prey, and showed a similar choice to feed or not on the water and plant. Thus, the predator P. nigrispinus exhibited feeding behavior driven by the availability of the moisture source. Despite the greater time of feeding on prey, predators gained weight in all food items indicating significant ingestion of food material. Therefore, these results characterize the role of the moisture source on P. nigrispinus predatory behavior, indicating it as one factor that should be considered when studying predation rate with this and other predators with extra-oral digestion.

RESUMO Predadores com digestão extra-oral devem considerar vários fatores para atacar uma presa baseado na sua necessidade nutricional e no investimento para a sua manipulação. Este estudo investigou o comportamento de escolha entre uma fonte de umidade e uma presa pelo percevejo predador Podisus nigrispinus (Dallas) (Hemiptera: Pentatomidae) e ganho de peso dependendo de sua escolha. Predadores adultos, após 48h sem alimentação, foram submetidos a três tipos de escolha: (i) água e pré-pupa de Alabama argillacea (Hübner, 1823) (Lepidoptera: Noctuidae), (ii) planta hospedeira (algodoeiro) e lagartas de A. argillacea (iii) e cada fonte de alimento individualmente. P. nigrispinus exibiu escolha similar entre alimentar-se da presa ou de água e mostrou preferência por plantas em comparação à presa. Quando sem chance de escolha, os predadores preferiram atacar a presa e exibiram similar escolha em alimentar-se ou não de água ou planta. Observou-se que o comportamento de predação de P. nigrispinus foi influenciado pela disponibilidade de uma fonte de umidade. Os predadores, apesar de possuir maior tempo de alimentação sobre a presa, apresentaram ganho de peso em todas as fontes de alimento com ingestão significante de água e seiva de planta. Tais resultados caracterizam a importância da presença da água no comportamento de predação de P. nigrispinus e que a sua disponibilidade deve ser considerada em estudos de comportamento de predação com este e/ou outros predadores com digestão extra-oral.

Tropical House Gecko (Hemidactylus mabouia) predation on brown spiders (Loxosceles intermedia)

Brown spiders (Loxosceles spp.) are venomous arachnids, successfully adapted to urban habitats in Brazil. Loxoscelism became a serious public health problem in Paraná State, especially at the capital Curitiba, where the most abundant species is Loxosceles intermedia. Hemidactylus mabouia (Gekkonidae) lizards are synanthropic predators of arthropods. In this paper, we describe the predatory behavior of the Tropical House Gecko H. mabouia on L. intermedia under laboratory conditions. Twelve geckos were observed, and all of them fed on brown spiders (n=123 observations). The attack consisted of a fast run followed by one bite on the spiders abdomen or legs. The geckos did not attack L. intermedia anterior body parts, probably due to the fangs present in this region. Two Hemidactylus individuals were killed by L. intermedia bites: during a predatory encounter, and by an induced bite on a restrained lizard. The observations summarized in this paper show that H. mabouia could be used in the biological control of Loxosceles populations in human dwellings. However, additional field studies are necessary to quantify the impact of H. mabouia predation on urban populations of L. intermedia and other species of the same genus.