Best time of the year for crabs? Maryland blue crab season runs from April 1 to December 15, but the peak times are June to August. (cf. Spawning occurs over a period of one to two weeks, from May to September, with a minor peak in June and major peaks in July and August.)
And, according to this article on blue crabs this fall (2006):
Traditionally, the average Marylander eats their last crab during the Labor Day holiday weekend or when the weather begins to turn cool. This year, however, the smart Marylander will be seen consuming heavy, sweet Maryland blue crabs into the late fall. The season for Maryland blue crabs does not end until December 15th and that gives us all much more time to enjoy Maryland blue crabs at their best!
Maryland blue crabs are at their largest in the fall, after having grown all summer. They also have not shed their shell since late September, which makes them very full and heavy. An abundant supply of large crabs is available at seafood markets at very reasonable prices. The large supply has lowered the price dramatically and consumers should take advantage of prices of the very large crabs now.