Dr Ron has been answering questions on bumblebees for several years now:
Engina species = Bumble bee snails
Bumble bee snails, sometimes erroneously referred to as bumble bee Nassarius, are small whelks in the family Buccinidae. These snails are from one to two centimeters long. The shell is black or dark brown and has a yellow or white stripe spiraling around the shell. This gives an appearance that is not unlike the yellow and black banding pattern of some wasps or bees, hence the common name. These animals are characterized by a more-or-less rectangular aperture, with a thickened outer edge. This outer edge typically has several bumps or swellings on its inner or apertural side. In fully adult animals, the aperture may be quite narrow. There is a short, narrow "spout" or siphonal canal. These animals lack the groove behind the siphonal canal, further indicating that they are not Nassarius.
Buccinids are typically predatory, and Engina species are no exception. Some Engina species are known to prey on polychaetes, however the species found in aquaria, probably closely related to Engina mendicaria, are poorly known. Being buccinids, all Engina will be primarily predatory, but probably they will also be able to act as scavengers eating uneaten food or carrion. Bumble bee snails have occasionally been seen to eat other snails, although this is probably not their major food source in aquaria. They have been reported as not apparently causing any apparent problems, although these observations are generally from aquaria that have sand beds. In these aquaria, the snails are likely eating sand-dwelling polychaete worms.
Bumble bee snails are found in shallow water throughout the Indo-Pacific and are fairly hardy. They will do well at standard reef temperatures and salinities.
I do not consider these animals reef safe in the broadest sense, but they are small and if only a few are in a tank they are likely not to cause apparent problems.
Note - this was a response back in 2004. He had a similar response in 2002. I don't know if his position has changed since then (doubt it).
Good luck!
