Unique fossils of caddisfly larvae from Baltic amber and in situ amber formation in aquatic ecosystems

Amber is formed by tree resins in terrestrial habitats. Therefore, a preservation of animals living in water in amber may appear surprising. Still more and more finds of such animals were reported in recent years. The central question around these finds is, whether the animals became entrapped in the resin in their original habitat (in situ), or whether the aquatic animals have left their original habitat to become entrapped in the resin (ex situ). We report additional finds of caddisfly larvae (Trichoptera; Leptoceridae, Lepidostomatidae) in Baltic amber. Two of these still bear their cases, which should not be present for caddisfly larvae, which escaped the waterbodies and became entrapped ex situ. One of the two is preserved with additional caddisfly larvae as well as a larva of a seemingly aquatic non-biting midge (Diptera: Chironomidae) attached to its caddis case. These finds further support a possible in situ preservation of aquatic animals in amber.