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Trophic specialists are expected to possess adaptations that increase the efficiency of handling preferred prey. Such adaptations may constrain the ability to utilise alternative prey. Here we tested whether the ant-eating spider Euryopis episinoides possesses metabolic specialisations with increased efficiency in utilising preferred prey and decreased efficiency in utilising alternative prey. In addition, we investigated the contribution of genetic variation via maternal effects. We reared E. episinoides spiders from the first instar on two different diets, either ants (preferred prey) or fruit flies (alternative prey). Spider survival rate and increases in body mass were significantly higher on the ant diet. The total development time did not differ between diet groups, nor did the number of egg sacs per female or the incubation period. However, the number of eggs per egg sac and hatching success were higher on the ant diet. There was a genetic variation in several offspring traits. Our data support the hypothesis that stenophagous ant-eating E. episinoides have a metabolic specialisation on ant utilisation indicated by higher efficiency in utilising ants than fruit flies. While most individuals of E. episinoides were able to capture fruit flies, only very few spiders were able to develop and reproduce on a pure fruit fly diet, suggesting the existence of within-species genetic variation regarding the tolerance to alternative prey., (Copyright © 2016 Elsevier GmbH. All rights reserved.)

In this study, field and laboratory observations of the feeding ecology (natural diet, prey acceptance, prey capture behavior and capture efficacy) of the theridiid Euryopis episinoides Walckenaer, 1847 were combined to reveal its trophic niche and capture efficacy and to test the hypothesis that this species is an ant-eating specialist. Natural prey was investigated from individuals collected in southern Portugal and was found to contain only ants of several species. Prey acceptance experiments revealed that spiders accepted several prey types occasionally, but ants, termites, and fruit flies were accepted with a high frequency. Prey capture behavior was similar for four tested prey types (Formicinae and Myrmicinae ants, termites, and fruit flies). Hunting usually started with a wrapping sequence when the spider threw the silk from its spinnerets onto the prey while circling around it. Then the spider bit the prey and wrapped it in more silk. Afterwards the spider waited for some time until the venom paralyzed the prey. Finally, the spider attached the immobilized prey to its spinnerets and carried it away before feeding. Wrapping time, number of bites, and waiting time differed among the four prey types, with the longest wrapping time, the highest number of bites, and the longest waiting time recorded during the capture of Myrmicinae ants. We conclude that E. episinoides is an ant-eating specialist possessing an effective capture strategy for the capture of ants. Yet, E. episinoides spiders maintain the ability to capture alternative prey. [ABSTRACT FROM AUTHOR]