bob-tooley, you make a very good point and I am sure that many and equally good points can be made for either side of this argument. But can you ever convince the farmer who knows how caterpillars can undo his livelihood? Can you persuade the producers of horticultural plants (for beauty only) that caterpillars are not a menace? I forget the actual numbers but the leaf eating caterpillar's diet is about 72% water; carbon is about 50% of the dry matter. We may not be talking about a lot of organic matter. May I put out a consideration of my own?
We discard an amount of any commercial food crop just for appearances' sake. I have a sense that this is about equal to the crop loss from pests of that crop. But who will or can cajole the average cook to accept the head of cabbage straight from the farm and do the final cleaning at the kitchen sink? If that can be done, we may well be able to take our share and allow the insects to take theirs.
The payoff would be no chemical pest control.

Generally I post a disclaimer stating; 'nothing I write is intended for forestry or agricultural purposes, so I slipped up on this post. I agree we can work toward a chem-free approach if we recognize the 'niche' many natural species fit into. Your caterpillar diet percentage is right on, but then the same percentage also applies to leaf, so the use-return ratio remains the same... I'm more focused on the indiscriminate use of chemical pesticides by home owners simply because of the availability and advertising. I believe we have to work from our side of the controversy just as hard as the commercial suppliers do from theirs. and hopefully the difference between their finances, and our lack thereof, will be common sense and a better understanding. To be honest, my goal isn't to sell anyone on anything, or provide a how-to approach, but rather to possibly cause them to think in a direction they might not have considered before...

Consider also that this leaf eating caterpillar is depriving the plant of its ability to manufacture nutrients by photosynthesis and there fore that plant must use reserves, stored in the roots, until new leaves are produced to do that job. The trade off of allowing the caterpillars to eat the leaves is a much weaker plant more susceptible to plant diseases and other problems and probably a reduction in yield, if the plant is a crop producer.
It is probably not a real good idea to allow these kinds of pests to have their way with your ornamental or fruiting trees or other plants.

Yes, the caterpillar is composting my garden crops. But I *don't want* my garden crops composted -- at least not yet! I'll compost them myself *after* they're done yielding! ;)

I think a point that bob-tooley makes is that we need to be tolerant of a few critters nibbling at our plants. And we need to practice common sense about when it's reasonable to begin control measures.

I had to chuckle when reading Ronalawn's comment about the 'final cleaning'. The other night, while rinsing some freshly harvested leaf lettuce in the sink, I came across a couple of baby slugs. Though perfectly acceptable of them from my OWN garden, I don't think I'd be so tolerant if I brought them from the grocery store. And I'm the person who has to wear disposable gloves when handling grocery store produce!

Going back to the basics, plants and trees are the intended food sources for all non-photo-related creatures on earth...insects included, as well as fungus and other micro-species, so they are very the start of the natural food chain, and nature has provided them with a very large built-in 'loss potential' which allows them to be the supply for many and still retain their own health requirements. In an age which is looking into cleaning up the environment and protecting natural resources it becomes necessary to consider how nature provides for itself and it's own, and before we can fix something we have to first understand what and where it's broken... My point is; are we trying to fix something which isn't broken by overlooking the 'natural intent'?

Hey, if you want to be a hunter-gatherer rather than a gardener, that's your call. Gardening is encouraging specific plants to grow and yield for you. By it's very nature, it's unnatural. The whole goal of organic gardening is to do it as sustainably as you can, with minimal involvement of things that might adversely affect health or the environment.

Things eating weeds or things outside your garden that you don't care about == just fine.

Things eating your garden == not fine.

I actually always leave some weeds around for my pests to eat rather than my plants. In some cases, it's very effective (for example, velvetleaf for leafminers and smartweed for Japanese beetles). Others, not so much -- squash bugs, for example, are only interested in squash-type plants, which don't grow wild around here.