Emilio Jorge Powers wrote,
"I wonder why the Euglandina wipes out the Achatinella and Partulina
(native Hawaiian tree snails) etc etc on the Pacific islands yet they do
not seem to make a dent on the Liguus populations in South Florida. The
Euglandinas are native to Florida and SUPPOSEDLY were here before the
Liguus arrived."
 
Good question. Let's take an analogous case. Suppose that humans were
native to the Old World and then a few couples were moved to a Pacific
island, where they prospered at the expense of the native fauna. Since no
small part of a group could carry all the diseases and parasites of the
larger ancestral group in the Old World, the islanders must have started
out with only a few kinds of disorders. Also, the survivors of the rigorous
voyage are likely to have been fairly healthy. The result is that the
islanders might have herpes and the common cold, but lack leprosy and
measles.
 
I suspect that the Florida Euglandina have diseases and parasites that we
know little or nothing about, and which help to keep their population down
there. In Hawaii, they have only a few disorders and little to stop their
spread.
 
Of course, this is only one factor. Euglandina may have carried new
diseases to the snails of the island. Their prey may have no effective
defenses, such as hiding, being active at a different time of day, or
tasting bad. We don't know, but if we did, we might be able to stop
Euglandina in its tracks--er, trail. More likely, however, we may discover
that nothing can be done but to culture the native snails in a giant
terrarium. Is anyone doing that, by the way?
 
Andrew K. Rindsberg
Geological Survey of Alabama