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Abstract: Asking how prey respond to different species of predators helps understanding the repertoire of defenses prey exhibit. This approach may also add to the knowledge on the efficiency of prey′s defenses against each predator and allows studying the costs of being attacked by different predators. Here, we studied interactions between the predatory terrestrial flatworm Cephaloflexa bergi and the harvestman Mischonyx cuspidatus. The flatworm quickly strikes at the prey′s leg with its head, then crawls towards the prey′s body releasing mucus and thus subdues the harvestman. Harvestmen may release defensive chemicals and pinch the flatworm with spines on legs IV, sometimes cutting the predator in two pieces. We also experimentally assessed the benefits of harvestmen′ defense and the cost of being attacked by testing whether the chemical defense of the harvestmen is efficient against the flatworm and whether the harvestmen that had survived a flatworm attack would have their locomotion abilities hampered. Both hypotheses were corroborated. Previous studies on interactions between harvestmen and other predators, such as spiders and scorpions, had shown that defensive secretions and mechanical retaliation were seldom used and were often ineffective. Our results point to the exact opposite and suggest that different predators exert different selective pressures culminating in the array of defenses exhibited by the prey. [ABSTRACT FROM AUTHOR]

Abstract: Most empirical and theoretical papers on prey–predator interactions are for animals with long-range detection, animals that can detect and react to predators long before these touch the prey. Heavy-bodied and chemically defended harvestmen (Arachnida, Opiliones) are an exception to this general pattern and rely on contact to detect arthropod predators. We examined the interactions between the Brazilian wandering spider Ctenus ornatus with harvestmen (Mischonyx cuspidatus) or control prey (Gryllus sp. and M. cuspidatus immature, both with soft integuments). Considering a prey–predator system in which fleeing from or reacting to a predator at a distance is not possible, we predicted both a high survival value of near-range defense mechanisms and that mortality would be higher in the absence of such defense mechanisms. We also expected the predator to behave differently when interacting with harvestmen or with a control prey without such defense mechanisms. Our results from laboratory experiments partially matched our predictions: First of all, histological sections showed that the integument of adult harvestmen is thicker than that of immature harvestmen and that of crickets. Adult harvestmen were less preyed upon than the control prey; the heavy armature increases the survival rate but the secretions from the scent glands do not. The predator did behave differently when attacking harvestmen compared to crickets. Despite the large size difference between predator and harvestmen, the protection provided by the armature allowed some of the harvestmen to survive encounters without pre-contact detection, thus greatly reducing the reliance on long-range detection to survive encounters with predators. Harvestmen call for theoretical and empirical work on prey–predator interactions that take into account the possibility that prey may not detect the predator before contact is established. [Copyright &y& Elsevier]