Kleptoparasitism is assumed to be the main foraging strategy in some animal groups, such as the spiders of the subfamily Argyrodinae (Theridiidae). However, some species may also feed on silk threads, egg sacs, or even their hosts. The conditions determining these alternative foraging tactics remain unknown for most species. We performed field observations, stable isotope analysis and laboratory experiments to investigate kleptoparasitism and araneophagy of Argyrodes elevatus and Faiditus caudatus in webs of Manogea porracea (Araneidae). We evaluated the following hypotheses: (1) both species exhibit higher trophic positions than their hosts and closest to an araneophagic sympatric species; (2) host web selection is influenced by the presence of alternative resources (adult male and female, and egg sacs); and (3) they preferentially consume egg sacs instead of stored prey items. Both argyrodines showed higher trophic positions than their female hosts and closest to an araneophagic spider species. The invaders were found mainly on host webs with one adult and egg sacs and with egg sacs only. Finally, A. elevatus preferred to feed on prey captured by the host spider instead of egg sacs. We discussed the factors that can potentially determine the choices between foraging exclusively as kleptoparasites and consuming the hosts.

假设窃取寄生是某些动物群体的主要觅食策略，例如亚科 Argyrodinae (Theridiidae) 的蜘蛛。然而，一些物种也可能以丝线、卵囊甚至它们的宿主为食。对于大多数物种来说，决定这些替代觅食策略的条件仍然未知。我们进行了野外观察、稳定同位素分析和实验室实验，以研究 Manogea porracea 网中的Argyrodes elevatus和Faiditus caudatus的盗链寄生和食肉动物（蜘蛛科）。我们评估了以下假设：（1）这两个物种都表现出比宿主更高的营养位置，并且最接近于食肉性同域物种；(2) 主机网络选择受替代资源（成年雄性和雌性，以及卵囊）存在的影响；(3) 它们优先食用卵囊而不是储存的猎物。两种 argyrodines 都显示出比它们的雌性宿主更高的营养位置，并且最接近于食肉蜘蛛。入侵者主要在具有一个成虫和卵囊的宿主网上发现，而只有卵囊。最后，A. elevatus更喜欢以宿主蜘蛛捕获的猎物而不是卵囊为食。我们讨论了可能决定在仅作为盗链寄生虫觅食和消耗宿主之间做出选择的因素。