During my time at Stephen F. Austin State University, beginning in 2006, I learned how to identify plants, including edible plants. Among my mentors was Greg Grant, who was in charge of the SFASU Pineywoods Native Plant Center at the time and is now a well-known East Texas horticulturalist and public speaker. He taught me about many of the common plants that we encounter in the East Texas Pineywoods forest. He once plucked up a bittercress weed (Cardamine hirsute) and ate it right in front of me! It was here that I first learned what passionvine (Passiflora incarnata, also called purple passionflower or passionfruit) looked like and how it tasted to suck on the juice sacks that surround the seeds in the fruit. In my opinion, the juice is not quite as tasty as pomegranate, but it is still desirable, native, and edible. At the time, my husband was studying wildlife management under Dr. James Kroll (also known as Dr. Deer). He was kind enough to let me sample some of the passionfruit growing wild at the Whitetail Deer Institute. They were growing near an intermittent stream, and had the best flavor! Deer also feed on this fruit. It is a food source for many critters, both big and small, in the East Texas Pineywoods forest.
When I started gardening at my newly purchased house in Jasper, TX in 2018, my intention was to dig up three new passionvine sprigs in the spring, transplant them to the sunniest spot in my front yard, and raise my own delicious fruit juice snacks. Well, I had no problem transplanting and training the vine on a trellis made of Golden bamboo (Phyllostachys aurea). I had flowers blooming. I was so happy. Then, the caterpillars came. Looking up their spiny red and black features online, I discovered that I had Gulf Fritillary caterpillars (Agraulis vanillae). It turns out that Gulf Fritillarys exclusively eat various species of passionvine (Passiflora spp.) the same way that Monarchs exclusively eat various species of milkweed (Asclepias spp.). That’s ok. The Jasper, TX community was aspiring to teach its residents about butterflies and pollinators at their Butterfly Festival outreach each year. I figured I may let some caterpillars share my vine. Maybe when they became butterflies, they could be seen at the local butterfly garden. Perhaps the Master Gardeners and Naturalists would point out my butterflies to children and say, “Look! That one was born and raised right here in Jasper.”
What I didn’t realize is that the caterpillars were not going to share my passionvine. They were going to dominate it. They were going to demolish every leaf on the plants. More and more caterpillars hatched as the summer heat got hotter. I didn’t have the heart to pick off and kill the caterpillars to control the population. They ate the vine until there was nothing left to eat. The most tender leaves went first, and the broad shade leaves were eaten as a last resort. Some caterpillars became food for birds. Others managed to form a chrysalis. I never did see the adults emerge, but there were empty chrysalids left behind!
That was the first wave. Every leaf was gone. Eaten. With no food left, the caterpillars disappeared. The more woody portions of the vine sprouted new leaves. I thought, “Perhaps I will get fruit now that the caterpillars have gone.” Nope. When enough leaves had grown back and flowers began to bloom again, the butterflies laid new eggs. The eggs hatched, and the demolishing started all over again. I did not get any passionfruit that year. I did get passionfruit the next year, but it never ripened properly. I was rather frustrated. On top of that, it sends unseen roots all over, and pops up in the most unexpected places. I had sprouts in my garden and in my yard up to 8 feet from the host plant. If this plant turns out to be trouble, I sure hope people at least got to see many Gulf Fritillary butterflies all over Jasper!
I still liked tending to the vines. It grew so fast in the summer that I found new tendrils every day to train on the trellis. New sprigs kept popping up all over the yard. I kept several more than last year to provide even more food. Of course, some came up in my garden too. Those had to go! I intended to grow edible plants in the garden – the passionvine could have part of the yard. I just had to cut some more of that invasive bamboo next door and put it to good use! More trellis was needed for the increased number of sprigs to climb.
I did have in mind the benefit that the butterflies brought when it comes to pollination of my other garden plants. Managing the many extra sprigs was not too difficult, but again, I let more grow to provide even more food. The ones I didn’t want got mowed or clipped with hand pruners. Fashioning a homemade bamboo trellis worked well and will be expanded next year. The poles just have to be replaced each year due to weathering.
I suppose the next step in my pollinator management should be to research population dynamics to find out if I should let this first wave/second wave cycle happen. Perhaps I should be reducing the population when the demand for food exceeds the supply? When I do collect enough data and information to discover the best way to raise these caterpillars, it may make an interesting presentation at a Master Naturalist meeting.
Fast forward to July 2020. While I had decisively considered myself to be growing passionvine specifically for the caterpillars, I’ve only observed two caterpillars so far this year! I have seen an increase in the number of birds in my yard. Northern Mockingbirds (Mimus polyglottos) fearlessly land on my trellis while I am in the yard. There’s also a tiny, unidenitifed, brown/black, mottled-feather bird that flits in and out of the azalea bushes nearby. I’m sure these caterpillar predators contribute to the sharp population decline. There is also the possibility that the Gulf Fritillary population in the region is not booming as much this year. Cycles of population explosions and declines are normal in nature. A third possibility could be that the overall decline in pollinator insect populations is becoming noticeable even here in the Pineywoods forest – far from the big city where habitat fragmentation and habitat destruction are a serious problem. Whatever the case may be, as a result, I have triple the amount of leafy vines and no caterpillars to feed on it! I do have fruits, though. Just when I began to wonder, “What I will do with all these vines?”, the fruits started ripening! I guess this will be a harvest year.
I’ll be adding to the list of things to research: “Do caterpillars have an occasional ‘off’ year?” I’m really hoping for this option. It would mean I could raise caterpillars some years and delicious passionfruit others. Time (and more research) will hopefully provide me with an answer.
For those interested in reading about my experience with passionvine and Gulf Fritillary caterpillars in more detail, I keep a journal on iNaturalist – a place where anyone can contribute their observations to science with the help of a community of enthusiastic naturalists. In the journal, I’ve included various observations of other insects that have been attracted to the vines and a count of the chryallides that I observed in close proximity to the trellis. Click the link below to read more: