In aggressive mimicry, a predator accesses prey by mimicking the appearance and/or behavior of a harmless or beneficial model in order to avoid being correctly identified by its prey. The crab spider genus Phrynarachne is often cited as a textbook example of masquerading as bird droppings (BDs) in order to avoid predation. However, Phrynarachne spiders may also aggressively mimic BDs in order to deceive potential prey. To date, there is no experimental evidence to support aggressive mimicry in masquerading crab spiders; therefore, we performed a field survey, a manipulative field experiment, and visual modeling to test this hypothesis using Phrynarachne ceylonica. We compared prey-attraction rates among BDs, spiders, and control empty leaves in the field. We found that although all prey combined and agromyzid dipterans, in particular, were attracted to BDs at a higher rate than to spiders, other dipterans and hymenopterans were attracted to BDs at a similar rate as to spiders. Both spiders and BDs attracted insects at a significantly higher rate than did control leaves. As predicted, prey was attracted to experimentally blackened or whitened spiders significantly less frequently than to unmanipulated spiders. Finally, visual modeling suggested that spiders and BDs can be detected by dipterans and hymenopterans against background leaves, but they are indistinguishable from each other. Taken together, our results suggest that insects lured by spiders may misidentify them as BDs, and bird-dropping masquerading may serve as aggressive mimicry in addition to predator avoidance in P. ceylonica.

中文翻译：

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伪装的捕食者通过在蟹蛛身上积极模仿鸟粪来欺骗猎物

在攻击性模仿中，捕食者通过模仿无害或有益模型的外观和/或行为来接近猎物，以避免被猎物正确识别。蟹蛛属 Phrynarachne 经常被引用为教科书上的伪装成鸟粪 (BD) 以避免被捕食的例子。然而，Phrynarachne 蜘蛛也可能会积极模仿 BD，以欺骗潜在的猎物。迄今为止，还没有实验证据支持伪装蟹蛛的攻击性模仿行为。因此，我们进行了实地调查、操作性实地实验和视觉建模，以使用 Phrynarachne ceylonica 来检验这一假设。我们比较了 BD、蜘蛛和田间对照空叶的猎物吸引率。我们发现，虽然所有猎物，特别是双翅目农螨，对 BD 的吸引率高于蜘蛛，但其他双翅目和膜翅目动物对 BD 的吸引率与蜘蛛相似。蜘蛛和 BD 吸引昆虫的速度明显高于对照叶子。正如预测的那样，猎物被实验性变黑或变白的蜘蛛吸引的频率明显低于未被操纵的蜘蛛。最后，视觉模型表明，双翅目动物和膜翅目动物可以在背景叶子上检测到蜘蛛和 BD，但它们彼此无法区分。总而言之，我们的结果表明，被蜘蛛引诱的昆虫可能会将它们误认为是 BD，而锡兰蜘蛛除了避免捕食者之外，落鸟伪装可能是一种攻击性模仿。