Dear Blue Lobster:
We have 12 tropical red crabs 6 of whom have in the last 24hrs taken to living UPSIDE DOWN. They twitch and stretch and my poor girlfriend is convinced that they are going to die. Please can you reassure her that they are fine and just looking for a different perspective on life?
Thanks for your help.
Dear Gentle Sir:
While crustaceans sometimes strive to see the world from a different point of view than they are accustomed to, crabs are more likely to just remain cantankerous or "crabby," as their name befits them. I will be both blunt and honest: Your crabs are either molting or dying.
In the case of the former, keep the water temperature and chemistry as they are now. If the other crabs seem aggressive toward them, introduce a tank divider to keep the molting crabs safe while they are soft, or as the crabbing industry calls them, "turds."
If the latter is the case and your crabs are expiring, by the time this response is published it may be too late and for that I am deeply sorry. I will include your crabs in my vigils.
If they yet live, check healthy crabs for odd behavior. If it's a tank chemistry problem, all of the crabs are likely to die at some point. If there are high levels of nitrids in the water or the pH is more than a few tenths of a point away from neutral, fix these problems immediately! Remove any pennies from your aquarium and turn your tank filter up to eleven.
I also point you to the case of the upside-down crayfish, a similar but ultimately tragic situation.