As I write, we're deep into the hairy crab season. Though available year-round (mostly in Shanghainese restaurants), they are at their best from mid-September until the end of December. Also called mitten crabs, their names are derived from the long, fine hairs that cover their claws.
Female crabs are usually eaten at the start of the season, when their rich roe, which turns red and firm when cooked, is more abundant. Male crabs are prized for their "male roe", which stays soft and gooey even when cooked. You can tell the gender by turning the crabs upside down: the female has a wide, bell-shaped underbelly, while the male's is slender and pointed.
The best crabs are said to come from Yangcheng Lake, in Jiangsu province, but far more supposed Yangcheng crabs are sold than the lake could possibly support. There's a huge market for faux Yangcheng crabs and they bear the same stamps, laser etchings and tags as do the genuine ones.
Buy the crabs from a trusted vendor. If you don't know one, ask friends for an introduction.
A meal of steamed hairy crab is something I'd far rather enjoy at home than in a restaur-ant (although dishes containing hairy crab where the meat and roe have been labori-ously extracted are something I'll leave to the experts).
For one thing, it's much cheaper to buy the crabs from a vendor (where they're already expensive) than to pay even more at a restaurant. They're also easy to prepare and make for a convivial meal, as everyone is forced to roll up their sleeves and get their hands dirty - not something you can do in a formal setting.