Butterfly caterpillars are very specific with their diet. They will eat only one family or one type of plant. For example, Monarch caterpillars will eat only Milkweed. If all the milkweed in the world died, all the Monarchs would die.
Only 2 or 3 eggs out of 100 laid in the wild live to be an adult. Nature is full of predators, parasitoids, and diseases.
Your first step is to obtain a sufficient amount of pesticide free host plant or artificial diet for the butterflies you plan to raise. Some species of butterflies eat a vast quantity of leaf matter while they are growing caterpillars.
PESTICIDE OR INSECTICIDE AND DOG/CAT FLEA CONTROL
Insecticide will kill your caterpillars. In most cases, if you have purchased a plant which has been treated with pesticide, it will be safe to use eight weeks after it has been treated. If you purchase a plant which has been ‘organically’ certified, it still could be fatal to your caterpillars. (Insecticides are fatal whether they are organic or inorganic just as both a tree and a steel pole hitting you on the head is fatal. One is organic and the other is inorganic.) BT is acceptable for use on organically grown plants. If pesticide or insecticide is sprayed in the building where your eggs, caterpillars, chrysalises, or adults are located, it may kill them also. Dog and cat flea and tick control, both oral and topical, may also kill your caterpillars. Wash your hands thoroughly before you touch their rearing container.
START AND STAY CLEAN
Start with clean/disinfected containers for your eggs or caterpillars. Butterflies contract dreadful diseases. If your rearing containers have been used in the past, disinfect them even if you did not have a disease problem with your last batch of caterpillars. Washing in the dishwasher (without bleach) is sufficient because of the high water pressure, several cycles of water, and high temperatures during the cycles. If your container is too large for the dishwasher, soak it in a bleach/water solution and rinse well. If your container is mesh, it can be washed in the washing machine (with bleach) if it does not have wire inside it. If it is a memory wire popup habitat, it can be disinfected in the tub or sink indoors or in a container outdoors. Always, always, wash your hands before feeding or tending to your caterpillars. Always use bleach in an area with adequate ventilation.
When you find eggs or when your eggs arrive after you order them, immediately place them with the host plant. If they are on a leaf, you can simply staple or pin the leaf with eggs to the living host plant. If you are rearing them from egg in a container with cut food, add fresh tender leaves every day. Butterfly and moth eggs will dehydrate quickly in a building. Air conditioning and heaters remove humidity from the air. Although it is important to keep butterfly eggs from dehydrating, it is also important to prevent them from sitting in an airtight container. They need air. A closed container without air flow is a perfect spot for mold and bacteria to grow. When your caterpillars emerge from their eggs, watch them! Their first meal is usually their eggshell.
It is extremely important to feed hatchlings tender new leaves. Older leaves are often too tough and baby caterpillars simply die from starvation because they cannot always eat older leaves.