If there is a twilight zone of microbiology, there is also a twilight zone of ecology. Organisms form populations, species, lineages, clades, and ecosystems. The status of each of these is an open question, but they have many of the same features associated with life as described above. Perhaps the strongest case can be made for eusocial insects, such as some ants, bees, wasps, and termites. In several species, there are rigid distinctions between the castes that reproduce and those that do not, with many of the latter serving the role of caring for the young (Hölldobler &amp; Wilson 2009). One might note that entities above the organism level are as a rule less integrated and connected than the organisms that comprise them. This is perhaps a general feature of life: from the perspective of every item in the biological hierarchy, its parts are much more homogenous than it is. Our cells seem much more integrated and self-contained than our bodies, so, too, are individual insects more self-contained than the colonies to which they belong.