One of the easiest ways to acquire caterpillars for raising is to visit garden nurseries in springtime.  Checking the dill, fennel and parsley will often turn up black swallowtail caterpillars that can be easily raised to become adults. Save them before they get squashed by staff who may not know better. One way to determine if the garden centers will have caterpillars is to find out where their plants come from and where they are grown.  Some centers will grow their own herbs from seed within green houses where they won’t have a chance to be visited by adult female black swallowtails looking to lay eggs. It is however possible that once the plants are placed outside for sale they may be visited by black swallowtails looking for host plants on which to lay their eggs.  For this reason you can purchase plants without eggs/caterpillars and place them in your butterfly garden to attract and raise these insects in a natural setting.