There are 7 Eastern Black swallowtail caterpillars on the dill and fennel below.  They're by no means the pests here.  It's the house wrens and the parasitic wasps that carried them off to feed their offspring last summer.  In their earliest stages, the caterpillars are dark, covered in tiny spikes and they wear a patch of white across their "back" called a saddle. The butterflies lay their eggs on dill, fennel, Queen Anne's lace...and they nectar at butterfly bush and monarda in our garden.  This year, I'm placing window screening around the plants until they emergy from the chrysalis stage.