One hundred million years ago, a female sand fly settled on a sauropod for what turned out to be her final blood meal. Something startled the dinosaur, and the insect's dining was interrupted. She escaped the thrashing beast only to become trapped in the sticky resinous sap of an araucarian tree.
Her "straining, desperate movements attracted the attention of a small predator patrolling the bark, who nipped open a minuscule hole in the end of her abdomen, deftly pulled out the reproductive system, and devoured the protein-rich eggs. Some of the gut contents of the entrapped insect spilled out onto the fresh resin as life ebbed away. She lay on one side in a drop of spilled blood, disemboweled, head and mouthparts clearly visible, wings outstretched.... An additional resin flow entombed the small female fly" in what we now call Burmese amber.
Of the many large and small dramas of Cretaceous life that Oregon State University Zoology Professor George Poinar, Jr., and retired research scientist Roberta Poinar vividly recount in What Bugged the Dinosaurs?, this one is the most significant. For when the Poinars studied that remarkably well-preserved ancient event in their laboratory, they discovered that the dinosaur blood was infected with a pathogenic microorganism.
Had the fly survived to bite another beast, it might well have passed the disease along, much as insect-borne diseases are spread from animal to animal today. That is not the only way insects bugged dinosaurs. They often competed for the same food or were irritating biters, stingers, and parasites.
Of course, they had their beneficial traits as well. They were pollinators of plants that fed herbivorous dinosaurs. They were food for carnivorous dinosaurs or the animals on which they fed. They were the "Sanitary Engineers of the Cretaceous," playing a major role in the recycling the nutrients in dung and the vital chemicals in the bodies of dead animals and plants.