Butterfly Buffet: The Feeding Preferences of Painted Ladies
Can you imagine a world without butterflies? Although butterflies are insects, most people think they are beautiful, peaceful creatures and enjoy them as part of nature. They are also helpful as pollinators for plants and trees. But currently, seventeen species of butterflies are endangered, two are threatened and three are extinct (Prairie Frontier 2009). I've always liked butterflies, but I really became interested when I got a habitat as a gift and raised five caterpillars. I became even more fascinated after a field trip to a butterfly exhibit. I really enjoyed learning about butterflies so I decided to study them, with the hopes of one day doing a field conservation project to help them.
Butterflies are insects and belong to two groups: true butterflies and skippers. True butterflies (Papilionoidea) are split into many families. This project focuses on the species of butterfly called Painted Lady (Vanessa cardui ), which belongs to the brush-foot family (Nymphalidae) (Schappert 2000). The Painted Lady is also nicknamed the "Cosmopolitan" butterfly because it is the most widespread butterfly in the world (eNature FieldGuides 2009). They live year-round in warm areas, which is important because this project takes place in Arizona in December. Painted Ladies go through a complete metamorphosis of four stages: the egg or ovum, the caterpillar or larva, the chrysalis or pupa, and the adult or imago (Schaffer 1999). It takes 7 to 10 days as a caterpillar and 9 to 14 days as a chrysalis before the butterfly emerges (Insect Lore, 2009). As seen in Figure 1, adult butterflies have antennae, compound eyes, a proboscis, six legs, a hard exoskeleton, a pair of forewings and hindwings, and a three-section body (Schappert 2000).
I believe that the anatomy of the butterfly plays a role in which flowers attract them for feeding. The head has many sensors and on the bottom part of the head is the proboscis, which is like a skinny straw that the butterfly uses to reach down into a flower to drink the nectar. The compound eye is made up of thousands of eyes that help the butterfly see at wide angles (Prairie Frontier 2009). Butterflies can see a large spectrum of color, including ultraviolet light, and Painted Ladies have four types of color receptors so they can see patterns in flowers that we can't see (Stokes 1991). Because of its eyesight, a butterfly may be attracted to a particular color flower more than another color, or see the details in a flower's structure that attract it and cause it to show a preference for feeding on that flower.
The characteristics of flowers may also play a role in how they attract a butterfly for feeding. The flower has to be able to support the weight of the butterfly, and its legs have to be able to latch on to sit on the flower because butterflies don't hover while they feed (Boriqua 2009, Roth 2001). The shape of the flower or its blossom arrangement may also be a factor in attracting butterflies for feeding. Clustered flowers and flowers with spikes that have small, closely packed blooms may attract butterflies because they offer more sips of nectar in one visit. Daisy-type flowers might attract butterflies in this same way because the "button" in the center is really a group of miniature petal-less flowers packed close together (Roth 2001). But some large single flowers will attract butterflies too, although they have a limited amount of nectar in one flower. "Something important to think about is the length of the tube of the flower because the butterfly has to be able to reach its proboscis inside to drink the nectar" (Boriqua 2009).
Another important fact affecting a butterfly's behavior is that they are cold-blooded so they need warmth to be active, usually above 50°F. When the Sun shines, the butterfly spreads its wings to bask and gain energy. They are more active, including feeding, earlier in the day when it is warmer and sunnier, and at nighttime or on cloudy days they rest with their wings folded to conserve energy (Kracht 2009, Ortho 2001).
I thought of my project idea, did some reading research and then conducted interviews with specialists from the butterfly pavilion at the Desert Botanical Gardens in Arizona. The research question I asked is, Do Painted Lady butterflies have a preference for what flowers they feed on? My hypothesis was: Given a choice of flowers to feed on, the Painted Lady butterflies will display a preference for certain flowers because of the color or the structure of the flower, rather than feeding randomly. The dependent variable was the number of times a butterfly feeds on a flower. The two independent variables studied were flower color and flower structure. There were several constant variables: (1) type of butterfly (Painted Lady, Vanessa cardui ); (2) age of the butterfly (less than two weeks old); (3) habitat (size, materials, setup, feeding apparatus); (4) testing conditions (outdoor temperature above 50°F, sunlight); (5) length of the feeding time (three hours); (6) flowers (naturally grown, not cut from a florist).
The design for this project included 12 testing subjects (Painted Lady butterflies) split evenly into three groups. Each group participated in three experimental trials for each independent variable (color and structure), which were conducted over six days, with three hours of data collection each day. This was for a total of 54 hours of data collection spread over 18 days.
- 6 Butterfly Garden habitats (ordered from Insect Lore)
- 3 sets of Painted Lady caterpillar cultures (ordered from Insect Lore)
- sugar water solution (3 teaspooons sugar dissolved in 1 cup of water); kept refrigerated
- plastic lids or paper plates, and paper towels as needed
- 8 strips of wood (71/2 inches by 3/8 inch by 3/8 inch)
- 16 pieces of Styrofoam (11/2 inches by 11/2 inches by 2 inches)
live plants in bloom, in the garden or in pots:
a) flowering lantana in four different colors (purple, red, yellow, white)
b) flowers in the same color family of purple: sage (spiky flower), argyranthemum (a daisy- like flower), lantana (a clustered flower) and petunia (a large single flower)
- Order and receive by mail from Insect Lore six Butterfly Garden habitats (one for a growing habitat, four for testing, and one for a resting habitat) and three live caterpillar cultures.
- Set up habitats indoors and raise caterpillars following the instructions (Insect Lore, 2009). Raise caterpillars in culture cups (Figure 2). After all the caterpillars in a cup get into their chrysalises, pin the paper disk to which they are attached to the inside of the growing habitat (Figure 3).
- Build an apparatus to hold flowers for feeding. Cut wood and Styrofoam according to the materials list. Construct the apparatus (Figure 4) by attaching a foam block at each end of a wood strip with the wood positioned toward the top of the foam. Repeat, and this time position the wood toward the bottom of the foam so this wood strip can fit under the other. Position these two wood strips with foam blocks like a cross. Poke two holes in the top of each foam block to hold the flowers. Repeat to make three more flower-holding apparatuses.
- One day after the caterpillars hatch from their chrysalises, move four butterflies each into its own testing habitat . These will be the testing subjects for Group I. Leave the others in the growing habitat. All habitats are stored indoors except during testing sessions.
- Feed butterflies with the sugar water solution as follows: Wet a paper towel with solution. Crumple the paper towel and place it on a plastic lid or paper plate in the bottom of the habitat. Repeat when paper towel is dry. Important: Butterflies in the growing habitat are fed continuously. Butterflies in the testing habitats are fed with sugar water after testing is completed each day, and the paper towel is removed at 8 p.m.
- Testing: Check weather.com in the morning. Plan testing to start after 50°F when there is good sunshine. Vary the time to get the best conditions. At the decided time, set up the testing habitats by cutting and attaching flowers (Figure 5) to the feeding apparatuses according to testing schedule (see Figure 6). Observe for three hours and record the feedings on the data collection sheet.
- Criteria for feedings: A feeding is counted when the butterfly inserts its proboscis into the flower. Separate feedings are counted if the butterfly flies off the flower and then returns to it to feed again. It is not counted as a feeding if the butterfly only lands on the flower but does not eat.
- At the end of the three-hour testing session, remove the apparatuses and throw away the flowers. Feed butterflies with sugar water solution, as in Step 2, to be sure they get enough to eat.
- Testing is complete for the group of four subjects after three trials of both color and structure. Remove butterflies from their habitats after the six days of testing, and place them in the resting habitat if it is too cold to release them outside (temperatures must be greater than 50°F at night).
- Place four different butterflies into the testing habitats as Group II subjects. Repeat Steps 3-6 and follow the testing schedule. Repeat the same steps for the last four butterflies in Group III.
Data from all trials for Groups I to III testing what color flower butterflies prefer to feed on is in Table 1. Results show that Painted Lady butterflies prefer to feed on purple flowers and like white flowers the least. They fed on purple flowers 45% of the time, red flowers 24%, yellow flowers 22% and white flowers 9% of the time (Graph 1). Overall, the results show that Painted Lady butterflies do not feed randomly; they have a preference for feeding on purple flowers.
Table 2 shows the data from all of the trials for Groups I to III, which tested which flower structure the butterflies prefer to feed on. Results show that Painted Lady butterflies prefer to feed on clustered flowers and like the large single flower the least. They fed on clustered flowers 65% of the time, spiky flowers 20%, daisy-like flowers 10% and the large single flowers 5% of the time, as shown in Graph 2. The results show that Painted Lady butterflies do not feed randomly; they show a preference for feeding on clustered flowers.
To get extra information about which flowers were the butterflies' favorites, data was also recorded when a butterfly landed on a flower but did not feed at all, and when butterflies stayed to feed on a flower longer than three minutes at a time. Results in Tables 3-6 show that butterflies most often "landed only, without feeding" on white flowers (22% of the time) compared to purple flowers (1% of the time); and on large single flowers (71% of the time) compared to clustered flowers, which they never landed on without feeding (0%). They fed longer (greater than three minutes) on purple and red flowers (both 6% of the feedings) compared to white flowers (less than 1% of the feedings); and longer on clustered flowers (4% of the feedings) compared to large single flowers, which they never fed on for longer than three minutes (0%).
The data from this project answers the research question and supports the hypothesis. It shows that given a choice of flowers to feed on, Painted Lady butterflies do display a preference for certain flowers depending on the color or structure of a flower. They prefer to feed on purple flowers (45%) compared to other colors, and prefer clustered flowers (65%) to other structures. I was not surprised because my background research made me think that a clustered flower is a good choice because it gives a place for the butterfly to land and can support its weight, and also provides many sips of nectar close by to make feeding very efficient. Purple is a favorite color, and this may be because of the butterfly's eyesight. Butterflies can see ultraviolet light, and purple is the wavelength of visible light closest to ultraviolet, and that may be why butterflies are most attracted to purple. Purple may also stand out better against the green leaves of a plant. There was a large difference between these results, and the butterflies feeding on the white flowers 9% of the time and large single flowers only 5%. White is all of the visible colors being reflected, and maybe the butterfly cannot see that color as well and so is not attracted to it. I believe that the butterflies do not like large single flowers as much because they do not offer much nectar in one visit, and it may be hard for the butterfly to reach its proboscis deep inside because it is a bigger flower.
Another observation from my data collection was that when a butterfly fed on a flower it liked, it often stayed on that flower longer to feed. If it was an unpopular flower, it often just landed on the flower without feeding. Butterflies have sensors for tasting on their feet, so when they land on a flower they can decide right away if they like that flower or not. The data for landing only, without feeding, give extra support to show what their feeding preferences were. Purple flowers were a favorite of the butterflies, who landed on them only 1% of the time without feeding, compared to 22% for white flowers. Clustered flowers were a definite favorite, with no occasions in which a butterfly landed without feeding, compared to 71% of the time on the large single flower. They also fed longer on purple flowers and clustered flowers, which shows that they really do prefer these flowers.
I made many interesting observations during my data collection. At the start of this project, I planned on doing the testing inside because I knew that butterflies need light and warmth to be active. The room would be at a constant warm temperature, and I would have the lights on a schedule. I thought those would be the best conditions, but I observed that the butterflies were feeding very little or not at all, and mostly rested with their wings closed. I thought that maybe the butterflies need the light and warmth from the Sun to be active and feed. The moment I carried the habitats outside, they opened their wings to bask and soon became active. I also observed changes in their feeding habits depending on the weather; they fed more when it was sunny than when it was cloudy outside. If I could do this experiment again, I would do it in the spring when there are more types of flowers in bloom so I could have a wider selection to test. An idea for a future project would be to use different color flowers or different flowers that fit in the structure categories. It would be interesting to see what the feeding preferences are of a different species of butterfly, and how that might compare to Painted Ladies. I would be especially interested in Monarchs.
- Painted Lady butterflies display a preference for feeding on certain flowers rather than feeding randomly.
- Painted Lady butterflies prefer to feed on flowers of a particular color: purple flowers (45%); rather than red (24%), yellow (22%) or white flowers (9%).
- Painted Lady butterflies prefer to feed on flowers of a particular structure: clustered flowers (65%) rather than rather than spiky flowers (20%), daisy-like flowers (10%) or large single flowers (5%).
- Painted Lady butterflies feed more often and for a longer time on flowers that they like, with purple flowers and clustered flowers being preferred.
Biodiversity is the variety of all living organisms and the ecosystems that they are part of... It helps provide the basic human needs such as food, shelter, and medicine. It composes ecosystems that maintain oxygen in the air, enrich the soil, purify the water, and regulate climate. (CIEL 2009)
Because human society is growing quickly and uses a huge amount of resources, there has been a sharp increase in the loss of biodiversity, so it is important to remember that every living thing on Earth has a part in the circle of life. Insects are an important part of our world because they have the largest number of species and the largest number of individual organisms; "their combined biomass represents an important food resource for other animals, and they contain much of the raw materials for the energy and nutrients that are cycled through ecosystems" (Schappert 2000). So insects are a very important part of biodiversity.
Studying butterflies is important for general scientific learning. "It also gives important information about ecosystems because we don't completely understand what the role or impact of butterflies might be. Information learned can be helpful to preserve and restore habitats, as well as provide adequate food in migration pathways or exhibits" (Kracht 2009). Because insects have a reputation for causing problems, many people are not concerned about their conservation. Luckily, people are not as unsympathetic about butterfly conservation as they are about other insects, because butterflies need our help. Along with problems like weather, pollution and predators, butterflies are at risk because of habitat loss and ecosystem damage caused mostly by people. Butterflies need a lot of host plants to lay eggs on in order to reproduce well, and they also need flowering nectar plants to feed on. Without good habitats that provide both of these things, there will not be enough homes for butterflies, which could lead to a decline in their numbers and make them more vulnerable to extinction (Schappert 2000).
Putting This Work into Action
The Monarch butterfly is facing challenges because of habitat loss, climate change and human development; it is a protected species. This butterfly is unique because it is the only one we know of that makes a two-way migration, like birds do. Monarchs migrate because they are not able to tolerate cold climates during the winter. Monarchs on the East Coast of North America travel to Mexico during the winter, and those in the western U.S. north of the Rocky Mountains travel to California (Lockwood 2007, Nelson 2007). But where do Monarch butterflies that live south of the Rocky Mountains go? And are there ever eastern or western Monarchs that migrate on a different path? It has now been noticed that Monarchs migrate through parts of Arizona along the San Pedro River and through Guadalupe Canyon into Sonora (Arizona-Sonora Desert Museum 2009). This may be because of changes in their behavior, away from following their usual migration pathways, or because changes in climate are forcing them to go a different way. But Arizona should prepare to help conserve and protect Monarchs. Arizona has a hot dry climate, and nectar flowers are not always plentiful. Also, Monarchs only lay their eggs in milkweed, so that host plant has to be available to them. Conservation programs should be put in place so that Monarchs have proper habitats to use during their migration. Monarch migrations are considered "endangered biological phenomena" so it is especially important to protect these butterflies as part of biodiversity (Arizona-Sonora Desert Museum 2009). I believe that projects like this one may help the Monarchs in Arizona by educating people about butterflies in general, their necessary food sources and how to help by planting backyard gardens to provide habitats for butterflies.
I know that doing this project helped me decide on the conservation project I want to do: I want to set up a special habitat and get it certified by Monarch Watch as a Monarch waystation. I plan to work through my Girl Scout troop to find a sponsor location, and get volunteers and donations to set this up as my Silver Award service project.
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