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Without A Trace

October 3, 2009

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Recognizing what lives in and passes through your garden is an essential part of organic gardening. You prepare the soil, put up a wire fence to keep out the neighborhood dogs, and arrange the plants in the order you wish them to grow, but it’s a big world out there that ignores the fence and moves in for the duration of the growing season.

Tomato Hornworm on sacred datura, a plant in the nightshade/tomato family.

Tomato Hornworm on sacred datura, a plant in the nightshade/tomato family.

Though the idea may seem revolting to some, removing insect pests by hand offers the best view of the health of your garden and your soil. You don’t learn much and you kill a lot of good things if you simply mix a bottle of orange oil or neem to nail the pests when you see the first one. Broadcast spraying is a technique that is overused by many gardeners.

While it’s a slow process, hand-removal gives you time to see and recognize pests as well as the beneficial insects to leave alone. Tiny little golden egg sacs stuck to the underside of a leaf by a slim ¼ inch long filament are good. That inch-long striated golden thing glued to a branch? If it moves, it’s an “asp” or “flannel moth” that gives the worst sting you’ve ever felt in your life. But look carefully, because if it is a praying mantis egg case, you want it there. That fuzzy white thing? If it’s a mealy bug, it’s bad, but if it is a “ragmop” nymph stage of a ladybug beetle, it is good. The reason the ladybug is there? You may have aphids, and that isn’t good. Your plants are under stress, and the aphids know it.

Praying mantis are amazing predators to find perched in your garden, and the startling drone of the low-flying insect aircraft in the garden comes from the huge cicada killer wasp (an insect that digs a large mole-hill sized pile of dirt); they excavate to lay their eggs on a live cicada they’ve dragged down the hole.) Tarantulas and the black and orange tarantula hawk wasp have a similar relationship. Red spider mites, leaf-cutter wasps, moths, butterflies, tricograma wasps, honey bees, all sorts of things are out there, though you can’t see them all, just their evidence of passage. Some you spray for, some you put in your garden on purpose. Of the choices you make, the biggest should be how to get rid of the harmful bugs without killing the beneficial ones.

Getting near to full-size after a couple of weeks, this hornworm soon disappeared.

Getting near to full-size after a couple of weeks, this hornworm soon disappeared.

And what about the insects that have a foot in both camps? The first time you come face-to-face with one of the large green hornworms as they bulldoze through the leaves and fruit on your tomato or pepper or eggplant, chances are the reaction is powerful. Ewwww! Kill it!

Not so fast.

Hornworms turn up in various plants around the garden. I used to squash them, but after taking time to learn more about them, I now relocate them to plants they eat but won’t harm. Their huge pupas turn up in the garden dirt and under trees when digging in winter and early spring. The brown curly-tailed shells have a startling way of offering a sudden twitch if you disturb them. This year I decided I wanted to know more about their life cycle. Just how large do they get, how long does it take, and what does the transition to pupa look like? I took my cameras out to document his work a couple of times a day.

Last month, after 15 days of watching and photographing a tobacco hornworm, Manduca sexta, devour the leaves and flowers on a volunteer sacred datura (Datura spp) in a pot on my front porch, he disappeared. Apparently after he and his current leaf were knocked off by the rain dripping from the roofline he sought refuge from the water. I found him two-thirds of the way up an amaryllis five feet away.

Close-up of front end and tiny head on fat body of Tobacco Hornworm.

Close-up of front end and tiny head on fat body of Tobacco Hornworm.

I transplanted him back to my potted plant where he stayed only a few hours more before leaving again. He ate one more leaf before vanishing, so I think this process of being a big fat caterpillar and eating a leaf to the point where your weight pulls it off the plant is a quick way down, versus climbing off the plant. I wasn’t able to find him a second time. Two more tobacco hornworms turned up last week on a tomato plant and I moved them into a large datura, but I’m not going to try to follow them again.

I’ll be pulling weeds this fall and putting down mulch for winter, and if I find these pupas in the dirt I’ll leave them alone. I’ve seen sphinx moths at work and want to protect them; they are important pollinators. As a park ranger in Arizona’s Sonoran Desert at Organ Pipe Cactus National Monument I first encountered them hovering, hummingbird-like, around the tubular corollas of blooming shrubs. And one night at sunset, in Temple, Texas, I happened to look out the second story window of my home into the boughs of a huge blooming mimosa tree. It was filled with hundreds of magical hovering birdlike creatures, sphinx moths, I realized, who were drawn by the pink bottlebrush flowers of my tree. A photo could never do justice to that beautiful moment. This doesn’t mean I’ll stop using Bacillus thuringiensis (BT) in my garden to keep these guys away to begin with, but if they make it to a large size, I’ll relocate them out of harm’s way.

I’ve taken too long to write this essay; I watched the caterpillar and wondered when to stop and finally write about it. Obviously, the denouement of the first disappearance was the time. As one who writes for a living, sometimes finding the time to polish a piece and process the digital photos is the delay, as with this piece. I’ve have several other incomplete essays and find I may have to approach some of these projects as blow-by-blow chapters if I want to keep up with my own goals for this blog.

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