The color of the exoskeleton is brown or green, but the antennae are red, and adults have bright blue bands near the tips of their legs. In smaller individuals, the bands may be white. The legs and carapace are covered in setae, and the rostrum at the front of the carapace is triangular.
The blue band hermit crab reproduces in June and July near the summer time in northern waters. The male grasps female's shell and may carry her around for a day or longer, occasionally knocking his shell repeatedly against hers. Mating only last for a few seconds; both animals must nearly leave their shells to mate. There fore leaving the hermit crabs exposed to predators. Eggs are produced from May to July, and are carried on the female's abdomen; inside the shell.
The life span is usually around 10-30 years. Hermit crabs mate externally when the male deposits sperm that the female absorbs into her body with secretions. The female lays her eggs within days or months after fertilization. The eggs appear in a ribbon-like grouping that remain attached to the female for approximately one month before the mother deposits the eggs in salt water to hatch.
When hermit crab eggs hit salt water, they immediately open to produce small larvae-like or plankton swimming creatures called zoea. They develop by in stages, each stage lasting about a week. At each molt, they grow larger and add more appendages.