Butterfly Enthusiasts often run out of milkweed. What to do??? If caterpillars are large, within a few days of pupation, they can be fed alternative food if milkweed can’t be found. We do recommend that everyone who has access to common milkweed prepare for such an emergency by FREEZING LEAVES twice a year, but if one hasn’t prepared ahead of time and leaves aren’t available, what is one to do? Simple! Run, not walk, to the produce stand or grocery store!
Let us emphasize: This is ONLY for times you have no other option. It is NOT good for them. It is simply better for them than starving.
Monarch caterpillars will eat butternut squash and a few other raw vegetables. Yes. You read that right.
If you are raising caterpillars indoors and your caterpillars have eaten all the leaves off the stems of a milkweed plant, spearing raw butternut squash chunks on milkweed stems produces less mold and mildew and keeps caterpillars out of their frass. If caterpillars have been feeding from living milkweed plants, this is ideal. If they have been fed milkweed leaves on stems, squash chunks can be speared on the empty stems. If stems are not available, any stick will work fine. Remember – don’t use any type of stick or stem that may have been exposed to pesticide.
Speaking of pesticide, the most dangerous pesticide on vegetables that you may feed to hungry Monarch caterpillars is apt to be on Certified Organic vegetables. WASH the vegetables BEFORE you cut them. Wash and rinse the vegetable and your hands well. Bt (Bacillus thuringiensis) is a natural soil dwelling bacteria that is deadly to caterpillars. Organic growers use it for the express purpose to kill caterpillars. When you peel the vegetable, the knife blade can carry Bt bacteria into the flesh of the vegetable.
Most enthusiasts have found most success with butternut squash as a substitute for milkweed leaves. Some of the other vegetables that have successfully been fed to Monarch caterpillars in the last instar (last few days) are cucumber, zucchini, and pumpkin.
A day or so after eating vegetables, caterpillar’s frass (excrement) becomes the color of the vegetable. When the cubed vegetable is speared on a stem above the soil, frass will fall to the soil, keeping the vegetable clean and drier than if the vegetable is lying on the soil or on the bottom of a rearing container.
Cleaner and drier means less mold and mildew. Mold and mildew leads to disease and death very quickly. Vegetables will mold and mildew much faster than milkweed leaves which is why keeping the vegetable chunks off the floor of the rearing container is healthier for caterpillars.
Young caterpillars will eat the same vegetables that older caterpillars eat. It is extremely rare for young caterpillars to survive long on vegetables. They do not contain the nutrients necessary for their survival. We recommend feeding vegetables to caterpillars only in emergencies and only in their last instar. Remember, when possible, always freeze milkweed leaves every year just in case you or a friend will need them. When you run out of leaves and can’t find milkweed, it is great to have a bag of frozen leaves in the freezer. Even frozen milkweed leaves are not healthy for young caterpillars. Young caterpillars need fresh milkweed.
Enjoy the fun of raising caterpillars on unusual food when it is necessary. Enjoy yellow, green, and white frass. It’s best if you never have the experience. Although great in emergencies, it is not healthy for caterpillars. Fresh milkweed is always best. Frozen, thawed milkweed is second best. But no matter whether finished on milkweed or vegetables, watching your Monarch butterfly fly off into the sky is fantastic and worth every worry and stress.