Dear Blue Lobster:
I recently found myself babysitting a fiddler crab. I set up a small tank for him with rocks to climb and shells to hide in. I bought another crab and the only one I could find in my small city was missing one claw. I’ve had them together now for about one month and the new crab seemed very dominate, hogging food and chasing the other away whenever he got close, so I assumed I had a male. Well, last night they both holed up in the same large shell, which was a shock for me. Today she is hiding out. Should I be concerned? I’m afraid I may have a pregnant crab showing up soon. If that is the case, what do I do with all of the eggs? I read she will have hundreds of thousands! I’m not prepared for that at all! I’ve put a lot of effort into saving the life of the male and after reading your website, I do think I need to do more for the crabs. I’ve grown quite attached to them.
Dear Gentle Sir:
It appears as though your Fiddlers have "hooked up," the scientific term for mating. Do not confuse the term with current popular teen slang, however. Fiddlers actually do hook up using their specially adapted swimmerets, kept hidden within their curled tail, to grasp on to one another as the male forces his sperm load into the female.
There are a few ways to tell if your female is pregnant. One is to watch for odd behavior. If she begins eating unusual foodstuffs, such as aquarium plants, gravel, or her own feces, something has definitely changed physiologically within her. Depression and mood swings are another telltale sign. Is she staying in her cave longer than usual? Another way to detect pregnancy is to watch for mucus forming on her underside, which precipitates before her eggs flow down from her ovipositor.
So what do you do if your female is indeed pregnant? Comfort her. Her man has kicked her out and will no offer care for her children — in fact, he may try to eat them! Make sure she has plenty of nice landings she can climb out of the water onto and many deep caves she can disappear into.
Also supply her with round-the-clock food. Fiddler crabs are detrivores, meaning they'll eat just about anything as long as it's small. Makes trips to your local food co-op or farmer's market to procure organic veggie leftovers from their trucks and bins. Food from supermarkets are often sprayed with chemicals and wax, which are definite no-nos for a pregnant crustacean.
Once she's in berry (visibly carrying eggs) the eggs will hatch within two weeks. At this point it's time to decide how to isolate her and her brood from the other creatures in the tank, who will without doubt see the crab larva as tasty treats. You can relocate her, which threatens her and her brood with new water chemistry, move the other creatures out of the tank, which may be convenient depending on the number of tankmates, or install a partition which limits her space but makes life for the aquarium owner the easiest.
The children will need fed nothing special in particular since in their earliest stages they'll eat microscopic algae and detritus. As they settle down and begin molting, however, give them a small crumble of flake food daily. In some cases, where the crabs were isolated from food for too long, scraping your skin or shaking dandruffy hair into the tank will give them enough nourishment for the time being.
After the crabs begin to grow, only a small amount of the total will make it to adolescence. Use the Chimwich-Hayes equation to arrive at the ideal number of crustaceans for your aquarium and use the Internet to sell the others. Some species of Fiddler crab young can net as much as 69¢ per pound!
Good luck to you and your Fiddlers. Motherhood is a special blessing indeed.