Sometimes one chrysalis will pupate on another chrysalis. Swallowtail chrysalises are especially prone to choose to pupate on another chrysalis.
Although in many cases they both emerge fine, in many cases the first butterfly cannot emerge at all or can only partially emerge. The problem is that the second caterpillar has laid its silk mat on the first chrysalis, sewing shut the area where the adult butterfly emerges.
Chrysalises have special weak lines on the back of the thorax that split open when the adult butterfly is ready to emerge. The adult butterfly draws in air and pushes with its body, splitting these lines of the chrysalis, and emerges to pump its wings full of hemolymph and fly away. When another caterpillar has sewn these lines shut, the butterfly cannot emerge.
Water loosens silk. To separate chrysalises, first remove them from the area where they pupated. Remember, silk is stronger than the chrysalis itself. Many times chrysalises are killed because people have pulled on the chrysalis and the silk girdle cut into the chrysalis. To remove the chrysalises, first cut the silk girdle of the FIRST chrysalis from the rearing container. Wet the silk at the rear of the first chrysalis and gently rub at the silk and remove the first chrysalis.
After the chrysalises are removed from the rearing container, place them in water or under the faucet for about 10 seconds. Remove them and wait another 10 to 15 seconds. Gently rub at the edge of the silk on the first chrysalis, loosening it enough to be able to grip it at the edge of the silk mat. Pull gently until the silk and chrysalis pulls loose. Remember – pull the silk NOT the chrysalis.
After they are separated, carefully check the area of the first chrysalis where the adult will emerge, indicated by an arrow in one of the photos to the left. GENTLY rub it to be sure that all the silk has been removed.
Chrysalises can be placed on a paper towel on the bottom in any container that has rough sides. Containers with clear plastic or glass sides are not recommended for emerging adult butterflies. They do not see or understand that clear glass or clear plastic is a solid object. Their instinct to go to light is so strong that they will try to walk through the glass or plastic, not even realizing that it is even there. They will continue to walk in place so long that their wings will dry crumpled. They will never be able to fly. A mesh, cardboard, or foam container will work fine.
If you have a clear drinking cup, you can tear a strip of paper towel and lay it on the bottom and up one side of the cup. Lay the chrysalis on the bottom of the cup, as indicated in a photo to the left. Because the cup is so narrow, the butterfly’s feet will touch the paper towel and it will crawl up the towel to spread its wings.