High number of moth species are considered to be agricultural pests in their caterpillar stage. Birds and other arthropods often forage moths, but ecosystem services provided by temperate bats are just coming to light in past few years. Although there is no doubt that insectivorous bats forage upon adult stages of pest moths contributing to the quality and quantity of crops, it remains unclear how many prey items have foraged and therefore it is unclear if the amounts taken are sufficient for biocontrol. Molecular detection of pest moth imagoes in bat diet is a relatively new approach that only delivers present or absent data. Therefore, sorting contains of bat faeces using morphological size determination may lead to better prey quantification. As the number of consumed prey items determines the boundary between consumption and regulatory significance, we focused on (i) if indigestible moth body parts retrieved from faeces reflect the number of moths eaten, (ii) how size of indigestible moth body parts relates to the overall moth body size, and (iii) an accuracy of moth classification into size groups. Our results indicated that base frenulum (hook holding front and hinder wings together) width is the most suitable characteristic to determine body size of the moth, with a discrimination success exceeding 73% when placing the moth into one of four size categories. The size differentiation of prey within a faecal sample together with molecular identification and other semiquantitative methods allows for more precise quantification and could yet help confirm the importance of bats as biological control agents.

许多蛾类被认为是处于毛虫阶段的农业害虫。鸟类和其他节​​肢动物经常以飞蛾为食，但温带蝙蝠提供的生态系统服务在过去几年才刚刚曝光。尽管毫无疑问食虫蝙蝠在害虫蛾的成虫阶段觅食对作物的质量和数量有贡献，但目前尚不清楚有多少猎物觅食，因此尚不清楚所摄取的数量是否足以进行生物防治。对蝙蝠饮食中的害虫蛾成虫进行分子检测是一种相对较新的方法，只能提供存在或不存在的数据。因此，使用形态大小测定对包含的蝙蝠粪便进行分类可能会导致更好的猎物量化。由于消耗的猎物数量决定了消耗量和监管意义之间的界限，我们关注的是 (i) 从粪便中回收的不可消化的飞蛾身体部位是否反映了被吃掉的飞蛾的数量，(ii) 不可消化的飞蛾身体部位的大小与飞蛾的整体体型，以及 (iii) 飞蛾分类成大小组的准确性。我们的结果表明，基部系带（将前翼和后翼固定在一起的钩子）宽度是确定飞蛾体型的最合适特征，当将飞蛾分为四个尺寸类别之一时，辨别成功率超过 73%。