<p><strong>Aggregation behaviour of †<em>Clidicostigus arachnipes</em> Jałoszyński, Brunke & Bai (Coleoptera, Staphylinidae, Scydmaeninae) in Burmese amber</strong></p>

The extinct genus †Clidicostigus Jałoszyński, Brunke & Bai, 2017 of the scydmaenine supertribe Mastigitae is a small group comprising three species from late Albian to early Cenomanian amber of northern Myanmar (Ross, 2019). Members are characterized by the presence of distinct longitudinal striae of the elytra, the elongate median mesoventral carina, and the asymmetrical, approximately boomerang-shaped maxillary palpi (Jałoszyński 2018). Based on the exaggerated elongate spine-like setae of the first two antennomeres of †Baltostigus Jałoszyński, 2016 (Eocene Baltic amber) and †Clidicostigus, Jałoszyński (2016) and Yin et al. (2017, 2018a) postulated that the spiny basal part of the antennae may function as setal cages used for hunting fast-moving preys, e.g., springtails. However, this hypothesis was later falsified by Jałoszyński (2018) based on observations of extant species, which in contrast possess much shorter and thinner setae of the antennae, and act more like opportunistic scavengers. Except for the debatable behavior regarding the function of the antennae of †Clidicostigus, the biology of this genus is otherwise largely unknown. Here we report the first case of aggregation behaviour of †C. arachnipes in Burmese amber.