Blue Crab Mating

University of Delaware Sea Grant Marine Advisory Service

Blue crabs mate in brackish waters between May and October, peaking in late summer.

Ordinarily, females (red-tipped claws) mate only once, while they are in the soft shell state after the last molt. Males (blue-tipped claws) may mate any time during the last 3 or 4 molts.

Just before the last molt, the female secretes a sex attractant that calms the male's blue claw. The crabs then assume the doubler position (male carrying female) and might stay like this for 2 to 3 days before and after mating, which lasts 5 1/2 hours.

Females are about 1 1/2 years old at the time and will store the sperm for use in 2 or more spawnings during their 3-year life span.

After mating, the female migrates down the tributaries and bays seeking water of higher salinity. Two to nine months later (depending on if it's spring or fall), the female will attach 700,000 to 2 million eggs to the swimmerets on the underside of her abdomen.

Only 1 out of 1 million eggs will reach adulthood.

The orange eggs gradually turn yellow and finally dark brown during the 2-week incubation period.

Once hatched, the zoeae become part of the oceanic plankton and drift for 40 days or more, growing and molting through the megalopa stage to the first crab stage.

Source: University of Delaware Sea Grant Marine Advisory Service