In the wildlife version, brood parasitism of the cuckoo is world famous. Cuckoos drop their eggs in unsuspeecting birds' nests and when the cuckoo chick pops out ahead of their adopted siblings, they tend to shove the resident eggs off the nest to make more room for themselves.
In the office version, well...everyone's had one or more of these in their workplace. It's the stereotypical eat or be eaten 1980s style of workplace survival technique. They're the parasitic folk who try to overtake others' projects and even conversations, alliances, and friendships in an effort to make a place for themselves and demean and demotivate others.
What's the best technique to counteract these folks? First, don't let anything demean or demotivate you. Internal motivation and a strong grasp of your area of expertise and workload help do just that. In the case when the cuckoo senses they're not really getting anywhere, and becoming sloppy as they're increasing the pressure on others around them...I'd say document and converse about what the proper action is with trusted advisors--such as your supervisor.