When we look at a hive we usually only see the bees. Look closer and we see a host of other organisms so the hive starts to look more like an ecosystem. Other writers have described it as an organism in which the bees are just the mobile part. Both views are compatible, I think.
The most visible organism in the hive is the honey bee - Queen, Workers and Drones. Living in close proximity are Varroa mites and sometimes other tracheal mites. Each bee is host to a number of viruses. Deformed Wing Virus seems to be endemic. There more viruses than I can (or want to) list here.
Feeding on the comb are wax moth larvae. They eat the brood comb including propolis, stored pollen and presumably honey. I don't think that they invade occupied cells.
Down on the hive floor and around the edges of the hive are ants, slugs and red spider mites. A fair amount of sugar drops out of the hive as well as wax; bee parts; bee poo (but only when they are confined or ill); wax moth poo; and mites. I suspect that ants are collecting the bodies of mites from the hive floor in one of my garden hives.
Invading the hives are robbing Wasps and Bumblebees. Some Cuckoo Bumblebees apparently make nests in hives. A the hive entrance may be Hornets which catch and eat the bees. I've seen Sparrows feeding on the moribund bees which crawl outside the hive.
Back inside the hive are the organisms too small to bee seen. A sheen of bacteria, moulds and yeasts over everything. The mead which I made last year began a spontaneous fermentation caused by the Saccharomyces yeasts. Unfortunately the yeast was able to cope with the high starting gravity and the result was a stuck fermentation which I had to finish with a commercial yeast. The finished mead has an unpleasant aroma of TCP which is caused by poor yeast health.
This brief view only mentions those organisms which I've seen around my hives. There are an immense number and variety of micro-organisms and other organisms which are considered diseases and pests.