It takes only 45 seconds in water for persea mites to drown, and in their native Mexico summer rains naturally reduce persea mite populations. In contrast to persea mite's poor survival in water, some predatory mites are known to survive in water by floating, though we have not yet tested Galandromus survival in water. In general, predatory mites are rather mysterious, with only a handful of species even being known to science prior to the 1950s. Predatory mites can be particularly difficult to monitor and detect, particularly in tall trees like mature avocados, where sampling is generally limited to those few leaves within arm's reach. Thus, months can go by in which biological control may be working undetected on leaves not easily sampled.
Avocado is native to rainforests, and rainforest trees are noted for complex insect ecologies.
Indeed, in rainforests different insect species may live at different heights within the tree canopy. Thus, a ground level person may only be able to detect a small percentage of the insect species actually living in the tree. Complicating sampling and monitoring even more, predatory mites are very mobile and hard to detect. Sometimes predatory mites survive at very low population levels, almost undetectable, for long periods of time before suddenly exploding in massive numbers and providing biological control. Very few scientists study predatory mites, so the reasons for this are poorly understood.