[2] Jonah crabs possess a rounded, rough-edged carapace with small light spots, and robust claws with dark brown-black tips.

[4] Males and females grow at about the same rate before reaching a carapace width of 1.2–1.6 in (30–40 mm), which is about the size of gonadal sexual maturity.

[5] A study in Rhode Island Sound found a discrete molting season in June for smaller (carapace width less than 4.7 in (120 mm)) male Jonah crabs.

Male crabs in Rhode Island Sound with carapace widths above 4.7 in (120 mm) were unlikely to molt.

[6] After a period in the plankton as zoea, megalopa settle in the subtidal zone with no clear preference between cobble and sand substrates.

[10] Because Jonah crabs are a strongly preferred prey item for gulls, their survivorship is highest in deep water.

[13] According to stomach content analysis on individuals from the Gulf of Maine, the diet of Cancer borealis consists of mussels, arthropods, snails, and some algal species.

Once, they were considered a nuisance and a pest that stole the bait in the traps and they were thrown back in the sea by fishermen.