Giant Swallowtail butterflies are one of the largest species in the US. They are found in states east of the Continental Divide as well as in the southern part of the western US.
These butterflies lay eggs on plants in the citrus family; orange, grapefruit, kumkuat, etc. Along with trees that come to mind when we think of the word ‘citrus’, they eat plants such as Hercules’ Club, Hop Tree, and Prickly Ash.
They, like Black Swallowtail butterflies, also lay eggs on rue. If you have both Black Swallowtail and Giant Swallowtail butterflies laying eggs on rue, it can be handy to know that Giant Swallowtail eggs are orange/rust in color while Black Swallowtail eggs are cream/white in color.
When raising these caterpillars, remember that they rarely, if ever, move from citrus leaves to Rue. They normally will starve to death. They simply do not recognize Rue as food after eating citrus.
The caterpillars are called ‘Orange Dogs’ because of their occurrence on orange trees. It is one of the few butterflies that have a separate name for the caterpillar. There are several moths that have two names, like the ‘Hickory Horned Devil caterpillar’ and ‘Regal Moth’ as names for the same moth.
The young caterpillars look much like wet bird droppings. Older caterpillars looks like dry bird/lizard/critter poop. Of course one of the best reasons to look like poop is the fact that few critters eat bird poop.
The osmeterium of the Giant Swallowtail caterpillar is red. When the caterpillar is disturbed, it quickly bends backward, extends its osmeterium, and touches whatever is touching it. The osmeterium has an odorous liquid on it.
Before pupating, caterpillars empty their digestive tracts. Swallowtail caterpillars tend to have a ‘frass dump’ (the last expelled excrement of a caterpillar before it pupates) that is runny and somewhat pudding textured.
Swallowtail caterpillars prepare to pupate by attaching themselves by making a silk pad and button on an object. It crawls onto the pad and attaches its anal prolegs into the button. It then makes a silk girdle by touching its head down to the object, side to side, many times over. Each time it leaves a strand of silk. The strands together make a strong girdle that holds the butterfly caterpillar.
When the caterpillar pupates, its old cuticle simply slips under the girdle and slips off the caterpillar. The ‘skinned’ caterpillar is the chrysalis.
After two or more weeks, the adult butterfly emerges.
Butterfly Fun Facts 