When lobsters mate, the male deposits his sperm into the female before she leaves, but that doesn't mean that her eggs are fertilized right away. In some cases he hasn't provided enough sperm to fertilize all of her eggs -- there could be tens of thousands of them -- so she may seek out one or more additional males to get the job done [source: Gosselin]. But even then her eggs might not be fertilized, because the female decides when conditions are just right. She may store live sperm in her body for two years before using them to fertilize her eggs [source: NOAA Fisheries Service].
Once the lobster fertilizes the eggs, they may stay inside her for another year before she lays them. And then they can stay attached to her swimmerets -- the small legs under her tail -- for another 9 to 11 months [source: Cowan].
After they hatch, the larvae float for about a month before settling on the bottom of the ocean to grow. Only 1 percent of larvae make it to the bottom and in general, just two of every 50,000 eggs live long enough to become adult lobsters of catchable size [source: NOAA Fisheries Service]. The lengthy life cycle and small payoff help explain why female lobsters are discriminating about when they decide to fertilize and lay their eggs.