There are other difficult and borderline cases. For example, micropredators are small animals that, like predators, feed entirely on other organisms; they include fleas and mosquitoes that consume blood from living animals, and aphids that consume sap from living plants. However, since micropredators typically do not kill their hosts, they are now often thought of as parasites. As another example, animals that eat plants are generally thought of as non-predatory herbivores, contrasted with predatory carnivores, but when those animals eat seeds (seed predation or granivory) or eggs (egg predation), they are consuming entire living organisms, which by definition makes them predators. Many predators are also scavengers, but pure scavengers that eat only dead organisms are not predators. Animals that graze on phytoplankton or mats of microbes are predators, as they consume and kill their food organisms; but herbivores that browse leaves are not, as their food plants usually survive the assault. In the words of the paleontologist Stefan Bengtson, predation "involves much more than fanged beasts that pounce with a roar upon the hapless leaf-muncher. "