Q: This is our 21-year-old hermit crab, Leonardo Da Pinci, known affectionately as Crab-alicious, or just plain Crabby. Our daughter got Leonardo and a friend for her 9th birthday and I’ve been taking care of him ever since. His mate met with her demise many years ago.Leonardo periodically disappears, burrowing for as long as a few months, but keeps coming back to the same shell. How do we know whether Leonardo is a boy or a girl?

Leonardo lives in our kitchen in a terrarium, so we see a good bit of each other. He seems to interact with us, waving his (her?) feelers at us when we chat with him. Is that our imagination?

Why do most hermit crabs usually die so young yet Leonardo keeps on keeping on? We don’t do anything unusual — food, water, and an annual change of habitat — and heat. He burrows for months at a time and we worry that he’s passed on. How will we know when that happens?

—Judith Schagrin, Baltimore

A: Judith, it is so interesting to hear about Leonardo Da Pinci and what a name! Frankly speaking, my knowledge of hermit crabs is rudimentary at best but I’ll try to answer your questions as best I can.

Unfortunately, captivity does seem to shorten the life span of a hermit crab, however, in their natural environment and in well-maintained captive environments, hermit crabs can live 20-30 years. I think it’s safe to say that your excellent husbandry skills are a big part of Leonardo’s longevity.

While the burrowing may seem unusual to us, it is actually a very normal part of the hermit crab life. They burrow for protection and safety during the molting period, which in some cases can take up to two months.

Now, if you want to figure out if Leonardo is really a Leonarda, you’ll have to do some gentle investigating. If the crab is a female, on its underside, at the third set of legs, there will be two round openings called gonopores, which are a feature only present in female crabs.

Finally, you’re not the first hermit crab owner to experience what appears to be interaction from your crab. The more time they spend in your presence, the more comfortable they will become, so it sounds like the kitchen is a great place to keep Leonardo!

Ask The Vet is a weekly series by Dr. Devon B. Smith, a Baltimore veterinarian who is an associate at Madonna Veterinary Clinic in White Hall. Send your pet questions or photos to vet@baltsun.com.