I've been 'gardening for butterflies' for more than fifteen years now. In reality, 'butterfly gardening' is the same thing as 'habitat gardening'; butterflies are simply insects that everyone seems to appreciate. The most successful approach to habitat gardening is to plant for the insects first; they are the foundation of all other life, and really fascinating creatures. Once you start learning about different insect species and their life cycles you will be amazed at the incredible adaptations and associations that many invertebrates have evolved with.
Welcoming insects into your garden is as simple as avoiding the use of insecticides and using natural gardening methods. Insecticides kill everything; the bad, the beneficial, the good, and the beautiful; like butterflies and their larvae. Of nearly 1 million insect species identified to date, only 1%, or about 10,000 species worldwide are considered pests; but even these ‘pests’, in natural situations, have natural predators which help to keep their populations under control. When insecticides are used the natural balance between pest and predator is upset; and by destroying just one element in the complex web of life, every other part suffers.
Gardening organically, using compost, natural fertilizers and mulch to build healthy soil that in turn grows healthy plants attracts all sorts of life to the garden. For a lively habitat, create a garden with a rich diversity of plants; but avoid planting ‘one of each’. If possible plant at least three plants of each species to create a ‘drift’ and try to have something in bloom throughout each season. Let your garden be a little ‘messy’, and allow some particularly useful weeds to grow. Where there is a thriving, balanced population of insects there will also be all other kinds of life, such as birds, reptiles and amphibians, and mammals.
Many butterfly species have evolved in close association with certain plant families, and also, like birds, are often associated with distinct plant communities. The following information on the butterflies most commonly seen in Marin gardens is, therefore, grouped according to plant communities; with the exception of two species – Monarchs and Painted Ladies - that I think of as Migrant Species because they will pass through, and sometimes linger, in several different plant communities. And, I've grouped some butterflies together under Urban Habitats because they are so often associated with introduced weeds and plants commonly cultivated in gardens.
But first, I'll use the Monarch butterfly for a quick tutorial on basic butterfly biology. It is really important for the habitat gardener to learn to identify the different life stages of various butterfly species. The Monarch has been closely studied, and I have reared many generations over the years, so I'll use them as an example of the amazing process of metamorphosis. Many other butterfly species have not been so well studied; in some the larvae are rarely seen; in some the range of host plants have not been well documented. An observant habitat gardener can actually add to the scientific body of knowledge.
Monarch Butterfly – Danaus plexippus
The Monarch is a butterfly that almost everyone knows something about! Lots of children have studied the life cycle of the Monarch, usually in second or third grades; here's what they learn.
Butterflies are insects that go through a complete metamorphosis (holometabolus).
The four life stages are egg, larva (caterpillar), pupa, and imago, or the adult stage (which we call a butterfly).
These life stages evolved so there is a partitioning of available resources.
The Monarch has evolved in close association with Milkweeds (Asclepidaceae); they are a 'monophagus' species; their larvae do not feed on plants from other genera.
Monarchs are famous for their long-distance seasonal migration, which is a migration of the species; it is the descendent of the individual butterfly that left the over-wintering site in spring that returns to the same over-wintering site the following fall.
Monarch populations west of the Rocky Mountains overwinter on the California coast.
Metamorphosis of the Monarch Butterfly
The following photos showing the life cycle of the Monarch are part of a “Monarchs in the Classroom” program developed at the University of Minnesota; many thanks to Karen Oberhauser, from the Department of Ecology, for permission to use these photos for educational purposes.
In the adult (imago) stage of the Monarch butterfly, male and female can be distinguished. The male is usually larger, and more brilliantly orange, with a swelling on one of the veins of the hind wings; this is a pheromone gland.
The female is browner and the black vein lines are broader. The adults sip nectar from flowers through a feeding tube (proboscis) that is curled up under the head when not in use. The adults do not grow; the nectar simply provides carbohydrates for the energy required for flight and reproduction. The main purpose of adult life stage is to mate and lay eggs.
Proboscis, photo by Bob Stewart
The female can lay as many as 500 eggs during her life span; but each life stage is vulnerable to all sorts of predation, so only about one in 200 eggs actually survive all the way to the adult stage! She chooses the host plant carefully, and often lays her eggs on the underside of a leaf, or within a cluster of flower buds, where they are somewhat hidden. She rarely lays more than just a few eggs on any one plant. She will flit about the plant, lightly touching down to take a chemical reading first, and the curling the tip of her abdomen to get close to the surface of the plant. (10) This distinctive egg-laying behavior is easy to observe.
Female Monarch laying eggs
Egg and Larvae
The egg is pearly white, and about the size of a pin head; under a lense a beautiful ribbed pattern appears. The egg will hatch in about four to six days, turning dark just before the tiny larva emerges.
Upon emergence from the egg the larva is barely an eighth of an inch long; with a white body and a dark head. The first thing they eat is their own eggshell, and then they start to feed on the leaf. They feed in between the veins of the leaf, and often just take the surface of the leaf. Sometimes the tiny larva finds refuge amongst the flowers, feeding within a flower bud for the first few days. They are extremely vulnerable at this stage, since it takes a few days for the protective toxins to build up in their bodies.
Newly emerged larvae
Caterpillars are eating machines – this stage in the life cycle is all about eating and growing! During the course of their development they go through five stages, known as ‘instars’. In Monarchs this takes about 10 to 14 days; during that time a larva has increased its body size by about 3,000 times! Larvae have six legs, just like all insects, but they are also equipped with ‘prolegs’, which are fleshy protuberances, used to secure them to the plant they are feeding on. Between each instar, the larva sheds its skin, or molts. The old skin splits, revealing a new and larger skin, which the larva quickly sets about filling out again.
The larva will feed on every part of the plant, including the flowers and the seedpods.
Larva eating flowers
Larva eating seedpod, photo by Bob Stewart
Older larva often notch the midvein of a leaf before eating it. This may be to create a safe, hidden place to feed, but it also stops the flow of the milkweed latex, which can gum up the larva’s chewing mouthparts. Milkweed plants that have supported larvae grow new leaves within a few weeks.
Larva feeding on notched leaf
When the larva is ready to pupate it seeks out a protected location, often wandering far away from the host plants. It spins a silken pad, and then attaches itself to this pad with its anal prolegs. It will hang, upside down for about a day, and when the skin splits, the pupa is revealed beneath, and the body of the larva is now ‘cellular soup’.
The Monarch pupa, or chrysalis, is adorned with tiny golden flecks; these glitter with light and movement, and may help to camouflage the pupa by obscuring its form. There are many creatures that predate on the pupal stage, including large wasps that cut a hole right through it and eat the contents. The pupal stage usually lasts 10 to 14 days.
One of the final changes that takes place within the pupa is the development of pigmentation of the scales on the wings. The day before the butterfly is ready to emerge (eclose) from the pupa its folded wings are visible through the pupa. When it first emerges from the pupa, usually in the morning, its abdomen is very large, and the wings are quite small. The wings gradually unfold as the fluids in the abdomen are pumped into the veins of the wings. The butterfly needs a good perch to hang onto, and plenty of room for the wings to attain their full size and shape. It takes several hours for the wings to become hard enough for the butterfly to fly. The butterfly also needs to join the two parts of its proboscis together to create a tube through which it can feed. The butterfly uses its two front legs to manipulate the proboscis; it is a process which can be observed.
Monarch newly eclosed, photo by CT
Monarchs in Marin
About fifteen years ago I used to see Monarchs coming through Marin in the spring, usually April, heading inland to where the milkweeds were plentiful, and then again in the late summer on their way back to the over-wintering sites. For the last nine or ten years I only see them in Marin in the late summer and fall, usually late August through October. The females often still have eggs to lay, and if the warm weather holds, caterpillars can make it all the way through the metamorphosis and join their brethren at the over-wintering sites along the coast.
Metamorphosis is an amazing, but also delicate process, fraught with problems late in the season. I found a pupa attached to one of my nursery pots in November. This Monarch emerged from the pupa late in the month, and the wings hardened properly. It was very lethargic, so I brought it flowers to feed from, but still it did not fly off. Within a few days the butterfly expired, and on close examination I could see that it was not able to join the two parts of its proboscis together, and so could not feed.
Late fall Monarch, photo by CT
A Monarch butterfly in the garden, flitting from one flower to another seeking nectar, is a wonderful sight; once Milkweeds are established, and you also see their larva in your garden, there is great satisfaction in knowing that you have provided for the complete life cycle of an amazing insect!
Monarch on Verbena
Learning More about Life Histories
Two great books, with lots of detailed information about butterflies and their life histories are:
The Natural History of Butterflies, by John Feltwell
This book goes into incredible detail about life cycle, adaptations and plant associations. The butterflies described are mostly European species, but much of the fascinating detail applies the life histories of local species too.
Field Guide to Butterflies of the San Francisco Bay and Sacramento Valley Regions, by Arthur M. Shapiro and Timothy D. Manolis
This book is truly specific to our region with lots of details on local species. The book also has really good introductory information on butterflies, life histories, how to raise caterpillars, and local plants.