This is a spider, which was encased in tree sap while in the act of attacking a wasp. The sap turned to amber, leaving an incredible preserved scene, with even individual strands of silk from the spider's web remaining unbroken for 100 million years.

— The paper this is taken from (sits behind a paywall, unfortunately)

— Learn more about the preservation of bugs in amber at the website for NOVA's "Jewell of the Earth" documentary