Amber is a substance that is produced by tree sap. Anyone who has tried to climb a pine tree or handled the branches will get sticky hands. The sap is a defense mechanism that the tree uses to pitch wood boring insects and diseases. Trees under attack or with broken branches can produce copious amounts of sap. Tiny insects can easily become entangled in the sap and unable to free themselves.
In some cases, the insect becomes completely encased in the tree sap. The sap prevents oxygen and disease organisms from reaching the entrapped insect. If the sap is subsequently buried, it will harden over time and the insect inside the amber can be preserved for millions of years.
An ancient deposit of amber that formed over 100 million years ago, is being mined from from a site in Burma. Many previously unknown fossil insects are encased in the amber. Scientists are studying the amber and categorizing the species.
In a recent paper in Historical Biology, (10.1080/08912963.2011.603421) fossil expert George Poinar, Jr and cicada expert, Gene Kritsky have described the oldest known fossil cicada. The cicada was newly hatched, possibly only a few hours old when it became entangled in the tree sap about 110 million years ago. The authors note a remarkable degree of conservation of the front legs of the fossil larva with larvae of our extant periodic cicadas. The legs are adapted to a lifestyle of digging underground through the soil to feed on tree roots. This find pushes back the fossil history of cicadas from 40 million years ago to about 110 million years ago. Cicadas have lived on earth longer than we previously suspected.