Wednesday, July 29, 2009

Butterflies and the Vegetable Garden

Our garden started out as a butterfly habitat, and although many of the plants were destroyed by Hurricane Ike and its aftermath, the butterflies are still plentiful. We don't have many flowers right now, so most of the butterflies that visit are females looking for a host plant on which to lay their eggs. Some of our vegetable plants actually double as host plants, and I have noticed lots of eggs on our bean and cucumber plants, plus our fennel and our lime tree.

I am keeping a close eye on these eggs and caterpillars to make sure too much damage is not inflicted on our vegetable plants, and have had few problems so far this summer. There are several giant swallowtail caterpillars on our lime tree. These caterpillars are nicknamed "orange dogs" because of their affinity for citrus trees, and are quite a pest in some orange groves. This is easy to understand because the caterpillars become ridiculously large as they consume the tree's leaves. Our lime tree does not seem at all bothered by the caterpillars, which are so large they cannot hide. This makes them easy prey for the birds, lizards and other predators in our garden. They are not the prettiest caterpillar, instead designed to mimic bird guano and thus avoid attack, but they more than make up for it as butterflies. It's hard not to be transfixed when a giant swallowtail floats through the garden, and in Houston we are lucky to have these butterflies for a good part of the year. If you don't want the caterpillars eating your citrus tree leaves, plant some rue and move the caterpillars. They will be perfectly happy eating rue leaves instead of lemon or lime, and will still turn into beautiful butterflies.

Next to the lime tree is our bronze fennel. Here the black swallowtails lay their eggs. The creamy yellow eggs are easy to spot against the dark fronds, and they soon become caterpillars that change from black to brown to brightly striped as they grow. Though not quite as large as the giant swallowtail caterpillars, the black swallowtails become long and fat by the time they are ready to pupate. They are fascinating to watch as they change their appearance with each instar. These caterpillars are also voracious eaters, and there are often ten or twelve of them at a time, but our plants are still lush and healthy. The fennel was planted a few years ago, and has perennialized in our garden. The fact that the plants are so well established probably helps it survive the hoards of caterpillars.

More problematic are the gray hairstreaks and long-tailed skippers. The gray hairstreak is a beautiful butterfly with a false orange "eye" on the tip of its wing that constantly moves hypnotically to distract predators. This butterfly lays large clusters of eggs, in this case on our cucumber plant. There is no way our plant could feed that many caterpillars, and still have the energy to produce cucumbers. I picked off about half the eggs, and figured our garden predators will take care of many of the survivors. I felt guilty, but want to try to maintain a balance in the garden between the caterpillars and vegetables.

The long-tailed skipper is another very pretty butterfly, with two incredibly long fat tails that iridesce in shades of green and blue. The skippers have been laying eggs on almost every bean leaf and tendril they can find. The caterpillars make a little tent to hide away as they eat the leaves. These caterpillars have been fairly destructive, especially on our younger bean plants that don't have lots of foliage in the first place. I remove the caterpillars when I find them (which isn't difficult to do -- just look for a leaf that is cut and folded over) and send them to our indigo plants. Here they can eat with impugnity.

It was a big loss when we tore out the remainder of our butterfly garden earlier this spring. I had no idea that many of those butterflies would be perfectly content with our new vegetable garden. As long as we can maintain a healthy balance between caterpillars and plants, we now have the best of both worlds. The butterflies would definitely be missed if they stopped frequenting our garden, and sacrificing a few leaves seems a small price to pay.

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