By Penny Pawl, UC Master Gardener of Napa County
The tomato hornworm that so many gardeners detest has a beautiful future if we let it be. After a winter spent underground and when it is done with metamorphosis, it will become one of the loveliest and largest of the moth species.
We never get to see this moth because it only flies after dark. It is known as the sphinx moth or hummingbird moth. Some of them fly in a manner similar to the hummingbird.
During metamorphosis, a caterpillar transforms into a moth. The caterpillar's internal parts liquefy, reform and a moth is born. The same happens to butterflies and it is one of miracles of nature.
I found three of these giant worms the other day munching happily on one of my tomato plants. They blend in very well with the plant, and they are as big as my finger.
I gently pulled them off and inspected their grinding mouth parts. Then I put them under a large overturned bowl with some tomato leaves and the tomato they had been chewing on. The bow is resting on the garden soil.
Most people get upset when they see hornworms on their tomato plants. I get excited. I hate losing my precious tomatoes to them, but by putting them in a container, I give them a chance to complete their life cycle.
Many people agree with me. We like hornworms because they assist with Integrated Pest Management, a way of gardening and farming that relies on the good bugs to manage the bad bugs without the use of pesticides.
Hornworms eat your tomatoes, but in turn, the beneficial braconid wasp lays its eggs in many of the caterpillars. These tiny wasps develop within the caterpillar skin and eventually will kill their host. They emerge from the caterpillar looking rather like rice hulls on the back of the caterpillar.
This same process happens in other butterflies and moth larva and helps with pest management. Anise Swallowtail caterpillars, which feed on plants in the parsley and fennel family, also have parasitic wasps lay eggs in their eggs.
When the caterpillar completes its life cycle and transforms into a cocoon, it will drill into the soil to spend the next several months. I watched one do this and it was gone so quickly I was amazed. The following summer, when the weather warms, they will hatch and begin to fly around looking for places to lay their eggs. Tomato plants are a favorite host, but they like any plant in the nightshade family, including peppers, eggplants and potatoes
I have read that marigolds, basil, borage and mint will repel tomato hornworms if planted alongside the tomatoes. Their strong odors seem to repel the moth.
The hornworm begins life as a small egg laid on the underside of the leaf. The larva hatches and grows quickly, and as it grows it eats more and more of the host plant. After three to four weeks, it is ready to take that dive into the soil.
I raised two hornworm larvae in the house in a container a few years ago. The hornworms spent the winter in my refrigerator in a small jar with soil. When summer arrived, I moved them to the garden, but I fear the experiment was a failure. The three giants I just collected will be on their own when they decide to go into the next part of their life cycle.
UC IPM has this Pest Note on Tomato Hornworms:
http://ipm.ucanr.edu/PMG/GARDEN/VEGES/PESTS/hornworm.html
The UC Master Gardeners of Napa County are volunteers who provide University of California research-based information on home gardening. To find out more about home gardening, upcoming events or to submit gardening questions, visit the Master Gardener website (napamg.ucanr.edu). Our office is temporarily closed to walk-in questions, but we are answering questions remotely and by phone or email. Submit your gardening questions through our website, by email mastergardeners@countyofnapa.org or leave a phone message at 707-253-4143. Master Gardeners will get back to you within a few days.
Somehow we missed this in July. We posted the article on our Facebook page. Have you visited AND LIKED us at UC Master Gardeners of Napa Valley? Please do!
We missed posting this to our blog. Penny Pawl, our extraordinary butterfly caretaker, explains how planting fennel led to so much else in her garden! You will notice a change in the font size partway through the article. The original does not have this change. I have tried to change it on this page, and have resized the original twice, to no avail. It posts those paragraphs in enormous font size. Think that's why it was skipped--because I couldn't fix the font.
Fennel is a Mediterranean plant that has been introduced to the United States. Over many years, it has naturalized in our area. Recently I saw an anise swallowtail butterfly visiting my fennel (Foeniculum vulgare) so I went out and looked for eggs and babies. The babies look like bird droppings as they are black with a white strip through their middle. In this search and subsequent ones, I discovered many small bugs living in the fine leaves of the fennel.
I originally planted this fennel to attract butterflies. The anise swallowtail is a beautiful yellow and black butterfly that especially likes the nectar of lily-of-the-Nile (Agapanthus). A few years ago, I was raising four anise swallowtail larvae and suddenly all but one died. I continued to watch the survivor until, one day, a small larva hatched out of his side. Then the caterpillar died.
I decided to observe what the larva turned into when it hatched. It was a small parasitic fly, and it had laid the egg before I had collected the caterpillars.
Butterflies of all species have a rough time laying eggs and raising them to full-size adults. That's why I take the time every summer to raise as many larvae as I can in my house. As soon as they pupate, or hatch, I let them pump up their wings and leave.
As I worked my way around the fennel, I found two tiny black-and-white spiders. Each one had created a web, and as soon as the spider caught an insect, the insect was carefully wrapped in the web and stored for the future. Both of these guys stayed close to their catch to guard it. They left only to gather more insects.
The one bug that puzzled me was an almost-yellow stink bug. Although I am always watching bugs, this one was completely new to me. over several days, I observed him. He moved to my milkweed plants, which concerned me, so I captured him in a jar.
I was finally able to identify the bug as a redshouldered stink bug (Thyanta pallidovirens). It is considered a good bug compared to many stink bugs and the invasive brown marmorated stink bug (Halyomorpha halys). Most stink bugs feed on and damages plants while the redshouldered stink bug eats other insects. All stink bugs have a straw-like mouth, the brown marmorated stink bug and plant feeding stink bugs carries theirs down their stomach and the redshouldered stink bug has his pointed forward. I did observe him sucking on a dead bug but a live insects would be his preference.
As my fennel is finally preparing to bloom there are many small flies and wasps visiting the buds. The swallowtail caterpillars are growing. In fact one has already left the pupa and is hopefully laying more eggs.
To raise the caterpillars in the house, I collect the eggs or very small caterpillars and put the them into small containers. When the eggs hatch the caterpillars are about 1/8 inch long. I add more fennel daily and clean ou their droppings. After shedding and eating their skin four times, they change from black and white to green with yellow and black markings. By this time they have tripled their size. (This size increase is common to all butterflies in the swallowtail family.) This amazing growth rate is the reason they shed their skin. After turning color, they eat without stopping. I have to transfer them to a larger container and I feed and clean their droppings twice a day. All they leave is fennel stems stubs.
Before the form a pupa, they go on a walk around the container. Once they settle down, it is a few hours before the skin covering opens for the last time revealing a pupa. This will be their home for weeks or even months. Most will spend the winter or "overwinter" in the pupa and emerge in the following spring to begin the process over again.
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. U. C. Master Gardeners of Napa County ( http://ucanr.edu/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.
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[Ed note: Pictures of their favorite flowers and the associated butterflies are posted in the order listed by Penny Pawl.)
This has been a beautiful, bountiful year for butterflies in my garden. I have been hand-raising butterflies for many years now. It's my effort towards giving them a better chance at life.
Butterflies start in March when the flowers and vines begin to put out flowers and leaves. The Dutchman's pipevine (Aristolochia macrophylla ) puts out its little pipes in March. These blooms are pollinated by gnats. The leaves start to grow about the same time, and the Pipevine Swallowtailbutterflies are programmed to leave their pupae at this time. Most of them have been waiting almost a year to complete metamorphosis and are happy to be flying in the sun, gathering nectar from flowers and laying eggs.
When I see a female laying eggs, I search through the vine and usually find eight to ten little golden eggs in a cluster. Before a predator can get to them, I take the eggs in the house and put them in a small container. The container keeps them and the leaves from drying up. In less than a week, the tiny caterpillars are born. At that point, I know that I am committed for five weeks before they will make a pupa.
Once I commit to raising them, I clean their containers daily and make sure they have plenty of pipeline leaves, their preferred food. Occasionally I run out of leaves from my vine, but I know where another vine is and I will 'borrow' some of its leaves.
Monarch butterflies make their first flight through Napa Valley in April and May, heading north. To be ready for them, I grow a number of types of milkweed (Asclepias) that bloom at different times in spring and summer. The native milkweed (Asclepias speciosa) is usually growing when the Monarchs pass through. They may lay eggs if the plant has tender young leaves.
This past spring I gathered about 20 Monarch eggs. They are small, white and found on the underside of milkweed leaves. When I gather the eggs, I take a piece of leaf with me so when the eggs hatch they have some food. Right now the butterflies are ignoring Asclepias speciosa as the leaves are old. Instead they are laying their eggs on narrow-leaf milkweed (Asclepias fascicularis). I have lost count of the number of Monarchs I have raised in my house this year, but it must be around 50.
I was gone for a couple of weeks in June when another group of Monarchs came through the garden. Every milkweed variety that I grow had been munched. I found caterpillars of various sizes and took them inside to complete their growth. Monarchs take less than three weeks to mature and become a pupa. They will emerge from the pupa in another two weeks. Since they are hatching in my yard and I have plenty of flowers, they stay a while and lay more eggs.
Anise Swallowtail Butterflies feed on fennel (Foeniculum vulgare) and members of the parsley and carrot family. My fennel had struggled for years as gophers love it, too. I finally put the plant in a large pot to protect the roots and sunk the pot in the ground. The roots grow out the holes in the pot and the main plant is saved. This seems to work, and I have found tiny caterpillars on the fennel. So far this year, I have more than 20 that are either in pupae or eating fennel like there is no tomorrow.
All three of these members of the Swallowtail family taste bad to birds. However, that does not stop spiders, wasps and native bugs from dining on them. Lizards also like them. A few years ago, small parasitic flies laid eggs in one group of Anise Swallowtails I was raising. This killed the caterpillars when the eggs hatched.
These butterflies live only six to eight weeks. During that time they will lay 500 to 600 eggs. Not all the eggs are fertile; some are defective and the newborns die before they mature. But by hand-raising them, I am giving more butterflies a chance to have their flying days. In nature, only a small percentage make the transition.
When I started raising the Pipevine Swallowtail, I saw only a few, but now many visit my vine all summer long. Last year, in late September, two large Pipevine caterpillars were still feeding on the vine.
You don't have to hand-raise butterflies as I do, but you can help them survive by planting nectar plants. Grow native Pipevine, native milkweeds and other plants that butterflies need to lay eggs and feed. Never use pesticides; butterflies are not immune.
Gardening for Butterflies is an excellent resource. You'll also find a lot of good information on the life cycle of butterflies online.
Tree Walk: Join U. C. Master Gardeners of Napa County for a free guided tree walk through Fuller Park in Napa on Monday, September 12, from 10 a.m. to 11:30 a.m. Registration is recommended as space is limited. Meet at Fuller Park, corner of Jefferson and Oak Streets. Online registration or call 707-253-4221. Trees to Know in Napa Valley will be available for $15. Cash or check payable to UC Regents. Sorry, we are unable to process credit cards.
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. U. C. Master Gardeners of Napa County ( http://ucanr.edu/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.