South America is the home of the largest bumblebees in the world, known as the "giant bumblebee" or its scientific name "Bombus dahlbomii."  These bees are found throughout Patagonia (the southern area of South America) but recently they have come into danger.  In 1997 European white-tailed bumblebees, B. terrestris, were brought into Chile for pollinating purposes.  Around 2006 the European bees escaped their secluded habitats and got into the wild, while at the same time the giant bees began to disappear from the area.  Many scientists believe the reason for this disappearance is due to a fatal single-cell parasite that came over to South America with the European bees, much like how Europeans brought diseases such as smallpox to America in the 16th and 17th centuries.  The parasite, Apicystis bombi, starts with a gut infection and then spreads to the rest of the body causing behavioral disorders. 

Some scientists still believe this parasite from the invading bees is not the reason for the decline in the giant bee population.  These people argue that it is because there is now more competition for food and other resources in the area.  To this the scientists who support the parasite theory say that there would not be competition for food because the two different species of bees have different eating habits that would prevent them from sharing the same types of foods.  There is some worry about the effect the parasite could have on other things such as plant life in the area.