Defensive mechanisms in blister beetles (Coleoptera: Meloidae) include a wide variety of behavioral responses, chemical defense, and conspicuous external colorations. Although some of these mechanisms have been previously described, proctodeal extrusion, a defensive behavior involving the extrusion of inner abdominal membranes from the proctodeal region which appear intensely red or orange colored when the hemolymph is seen through them, has not been reported to date. Here, we tested the ability to display proctodeal extrusion in response to threat stimuli in wild populations of three blister beetle species inhabiting Central Spain: Berberomeloe majalis (Linnaeus, 1758), Berberomeloe comunero Sánchez-Vialas, García-París, Ruiz & Recuero, 2020, and Physomeloe corallifer (Germar, 1818). In addition, we observed and recorded various other defensive behaviors such as immobility, antennal threat display, autohemorrhage (reflex bleeding), defecation, and thanatosis (death feigning). The frequency at which proctodeal extrusion was observed differed among species, as did the stress intensity needed for extrusion and the probability of proctodeal extrusion in response to a particular threatening stimulus. Our findings indicate that, although proctodeal extrusion might be a widespread potential defensive mechanism in Meloidae, the ability to elicit it is not generalized across lineages. Physomeloe and Berberomeloe are endemic to the semi-arid Mediterranean region, and species adapted to such a climate would have developed strategies that limit hydric stress such as proctodeal extrusion, which mirrors the effect of autohemorrhage but without the fluid loss.

泡状甲虫（鞘翅目：Meloidae）的防御机制包括多种行为反应，化学防御和明显的外部着色。尽管先前已经描述了这些机制中的一些机制，但迄今尚未报道过直肠前突挤压的防御行为，该防御行为涉及从直肠前突区域挤压出内腹部膜，当通过它们看到血淋巴时，腹部内膜呈现强烈的红色或橙色。在这里，我们测试了居住在西班牙中部的三种水泡甲虫物种的野生种群对威胁刺激显示出直肠切除的能力：Berberomeloe majalis（Linnaeus，1758），Berberomeloe comuneroSánchez -Vialas，García-París，Ruiz＆Recuero，2020和Physomeloe Corallifer（1818年，格尔马）。此外，我们观察并记录了其他各种防御行为，例如固定不动，触角威胁显示，自体出血（反射性出血），排便和死亡（死亡假装）。物种之间观察到的直肠挤压的频率不同，挤压所需的应力强度和响应于特定威胁刺激的直肠挤压的概率也有所不同。我们的发现表明，尽管直肠前突挤压可能是根结线虫中广泛存在的潜在防御机制，但引诱它的能力并未在各个血统中得到普遍体现。Physomeloe和Berberomeloe 是半干旱地中海地区的特有物种，适应这种气候的物种将开发出限制水应力的策略，例如直肠挤压，这种方法可以反映出自体出血的影响，但不会造成液体流失。