This is a follow-up post to Butterfly Gardening for Adults.
So you’ve planted nectar flowers and attracted lots of adult butterflies to your yard, and now you want to see if you can add species diversity. Or, perhaps you want to observe these beautiful insects during any or all of their other 3 life stages. With just a little bit of effort you can rear a butterfly from an egg to an adult, right in your yard.
An adult female butterfly has one main motivation: find the correct plant and lay her eggs. What do I mean by “the correct plant”? It turns out that most species of butterflies are picky about where they’ll lay their eggs. Monarchs famously lay their eggs on milkweed (Asclepias spp.), but most other species would find milkweed to be just as toxic and unpalatable as you and I would. If a monarch female laid her eggs on the foliage of a rose bush, her children would find the leaves inedible and they would starve to death. Because of this, butterflies (and people who study them!) need to be good botanists. Lepidopterists (scientists who focus their studies on moths and butterflies) often work with botanists, native plant societies, chemists, and others to try to understand how a butterfly decides where to lay her eggs. These plants are referred to as host plants, and they are a critical component of the butterfly life cycle.
Why would the Monarch caterpillars starve to death if their mother deposits her eggs on the wrong plant? Because plants produce chemicals (called phytochemicals) that give them color, produce fragrance, help carry out physiological processes, and defend them against enemies. Enemies of plants include fungi, bacteria & viruses, and herbivores (animals that eat plants). Butterfly caterpillars are herbivores. If they’re present in large enough numbers they can strip the leaves and stems from a plant, weakening or even killing it. Because of this, many plants have evolved the ability to produce defensive chemicals to reduce the likelihood that they’ll fall victim to herbivores. But, just like in an arms race, some herbivores have managed to overcome these defenses and exploit the plant in question as a food source. The milkweed- Monarch example is a great illustration of this. Milkweeds produce chemicals that are toxic to most herbivores (including humans), but the monarch has evolved the ability to ingest milkweed foliage without incurring damage from those chemicals. Monarch mothers can lay their eggs where very few other insects can, and her children will thrive.
So how do you decide which host plants to include in your garden? You can start by researching the host plants used by the adults that come to your garden. Butterfly field guides almost always include information on the host plant used by each species. If you want to attract new species to your garden, these same sources can help with that, too. Look to see which species you can expect in your area, paying close attention to the habitat type (e.g. if you live in a sage desert, you’re not going to get marshland species in your yard!) as well as to the geographic distribution. eButterfly is a great way to track what shows up in your yard as well as to see what species are showing up nearby. You can also keep an eye on wildflower gardens and nurseries in your neighborhood to see what other species of butterflies are around.
Once the eggs hatch out, the caterpillars will be very hungry. While a few species tend to lay
eggs on one host plant but spend their time as caterpillars on another, most stay on the same species for both life stages. For this reason you can usually accommodate eggs and caterpillars of a given species with the same plant. Be aware, though, that caterpillars can have voracious appetites. Very few butterfly species are considered to be crop pests in the US (a notable exception is the Cabbage White, Pieris rapae), but they can seriously defoliate your plants, nevertheless. If you have a vegetable garden, be aware that you may lose some things to caterpillars if you don’t find a way to discourage them. This is mainly true of crucifers and legumes, which serve as host plants to many species of sulphurs and whites. Anise, citrus trees, alfalfa, blueberry and cranberry plants, gooseberry plants, rice, figs,guava, and cherries are some of the other plants that might unintentionally become host plants in your butterfly garden. It’s unlikely that a colony of Giant Swallowtails, Papilio cresphontes, are going to seriously damage your lime trees, but a few Cabbage Whites can put a hurting on the mustards in your salad garden.
Caterpillars go through several molts, growing larger each time. We call these instars– after hatching from the egg, the caterpillar is in its first instar; after the first molt, it is in its second instar; etc. The number of larval instars varies from species to species but averages ~5. Once the caterpillar enters its final instar it will prepare for the pupal stage, also called the chrysalis. The caterpillar will prepare to pupate by crawling to a place that is (hopefully) safe from environmental extremes, predators, parasitoids, and has a good substrate for attachment. This might be its host plant, but is often a textured vertical rock face, a tree trunk, or, in a garden, a fence post or flower pot. The caterpillar will attach herself to the surface she’s chosen and build a complex structure around herself. She’ll then appear to go dormant for several weeks- several months, depending on species. In reality, though, there’s a complex developmental process going on inside that pupal casing! But that’s a post for another day. To make sure you are providing a place for your caterpillars to pupate, include some vertical surfaces like decorative rocks or fenceposts, and experiment with giving them a little shelter- a small overhang or roof can help protect the pupae from the weather. Once development is complete, the adult butterfly will emerge and the cycle starts anew.
Next time: Enemies in the Garden