Terrestrial insects are often remarkably well preserved in lacustrine Konservat-Lagerstätten. However, the assumption that carcasses should sink fast through the water column seems to contradict evidence that this scenario is unlikely due to excessive buoyancy and surface tension. The mechanisms that promote rapid and permanent emplacement onto the sediment surface (RPESS) of such terrestrial animal remains are not fully understood. Here we use taphonomic experiments to show that floating in water, growth of microbial biofilms and reception of rapid sediment load promote RPESS of terrestrial insect remains in lentic water bodies. Our results show that the optimum conditions for RPESS occur when terrestrial insects enter a lentic water body in articulation, experience brief decay in association with growth of microbes, then are buried rapidly by airborne volcanic ash. These results provide a model for preservation of articulated terrestrial insects and emphasize the importance of microbial activity and volcanism for insect preservation in lacustrine Konservat-Lagerstätten.

S0-S4 This text file includes S0–S4. S0 includes information about the fossil specimen sectioned in this study. S1 includes methods of measuring masses, dorsal surface areas and static contact angles of the experimental insects. S2 and S3 are details of calculating the falling velocities and external forces of the clasts during the sediment load. S4 is a list of well-studied lacustrine Lagerstätten incorporated into the statistical analysis. S5_Experimental_records This spreadsheet includes measurements of insect characteristics and other parameters during the experiments, and the experimental records of Experiments 1, 3 and 4. S6_S9_Experiment_2 This zip file includes experimental records of Experiment 2 in four separated spreadsheets. S10_terrestrial_insects_lentic_PaleoDB This csv file includes the insect fossil records from "lacustrine", "crater lake" and "pond" deposits downloaded from the Paleobiology Database on 19th May 2019. Records of aquatic larvae and nymphs have been manually omitted.