Can empty bottles filled with seawater sand and small hermit crabs be brought on board a plane?

**Yes**. Empty bottles filled with seawater sand and small hermit crabs can be brought on board, but there are some rules and restrictions to be aware of. Depending on the laws and regulations of different countries and regions, bringing live animals into the country may require specific procedures and supporting documents. Additionally, during flight, environmental and pressure changes within the aircraft can cause significant stress and discomfort to small animals. Therefore, if it is necessary to travel with small hermit crabs, it is best to consult a professional veterinarian in advance and obtain a legal license, and also consult the relevant regulations and policies of the airline or local authorities.