Amber often contains organic inclusions such as insects, arachnids, arthropods, small amphibians, plants remains, grains of sand, and gas bubbles. They are the source of knowledge about the time when amber was formed, the animals living close to resin trees, and the ones active in the time of the resin leakage. The inclusions make amber even more special!
Amber is a treasure trove for paleontologist research. The body of transparent resin has preserved mummified animals as inclusions from 40 million years ago. The resin acted as a selective trap for animals which lived in the amber forest. It was mainly small animals which lived on the resin-secreting trees or in their vicinity that would be caught in the tacky discharge.
True flies (Diptera) are the most numerously represented group of insects found in amber, making up over 70% of all faunal inclusions. Hymenoptera, including many types of ant and very occasionally bees, are the next most common group, accounting for 10% of insect inclusions in amber. The third most frequently noted group comprises beetles (Coleoptera), which are represented predominantly by individuals from families whose larvae live beneath the bark or in channels burrowed into the tree. Other insects commonly found in Baltic amber are Collembola (c. 5%) and Homoptera (c. 5%), featuring fairly large numbers of Aphidinea. These insects lived in colonies and a single piece of amber often contains several or several dozen specimens.
The most commonly occurring arachnids in Baltic amber, as in contemporary faunal assemblages, are spiders (Araneae) and mites (Acarina). Individual specimens of harvestmen (Opiliones) and false scorpions (Pseudoscorpionidae) have also been noted, the latter being of particular value, as the only examples of Paleogene Pseudocsorpionidae we know of have all been found in amber. Myriapods, which are rarely noted in amber, are represented primarily by millipedes (Diplopoda), most often of the family Polyxenidae, and by centipedes (Chilopoda), whereas Symphyla are known only from single specimens.
What we know of contemporary animals, in particular about their behaviour, ecology and physiology, can be used to gain a better understanding of extinct fauna. This is also true of animal inclusions in amber — most of what we know about them is based on our knowledge of contemporary fauna. Although no species from the amber forest has survived to this day, at higher taxonomic levels little has changed among the fauna of the amber-yielding forest.
A good basic knowledge of contemporary fauna is usually sufficient to identify and classify an inclusion to order or family.