The basic principal involves using natural enemies to eat the various pests, thus, keeping them under control and preventing damage to the plants.
The most easily seen natural pest controllers are the Chinese Painted Quail that you can see running around the flowerbeds amongst the foliage. These small flightless birds are used to control pests at soil level including ants, (which can carry butterfly eggs away to their nests for food), woodlice, earwigs and various other unwanted creepy crawlies. They also, to some extent, control spiders that spin their webs close to the ground, so preventing them from catching the butterflies. The quail do have their drawbacks because, although they cannot fly and so cannot catch the butterflies, they have been seen to take caterpillars that venture within their reach.
Other natural pest controllers are much less easily seen. For example, whitefly is controlled using a small parasitic wasp, which is only 1.5 mm long. The wasps lay their eggs in the larvae of the whitefly so preventing the adult whitefly emerging.
Another important pest to be controlled is the mealy bug. These are small white waxy looking insects about 3-4 mm long when fully grown. They form large colonies and cover themselves in a white cotton wool like webbing. They quickly destroy plants and need to be controlled using a predatory ladybird called Cryptolaemus Montrouzieri. This is a small insect, orange in colour with black wing casings, and about the same size as our own native ladybird. These are voracious predators and can consume over 150 mealy bug larvae each in a week.
Other greenhouse pests are controlled in a similar manner. During your time at the Butterfly Farm, see if you can spot any natural pest controllers for yourself.