Cabbage loopers, cabbage worms or just plain little green caterpillar. Common pest of plants particularly on brassicas. Hand picking works if you can get them all otherwise BT (Thuricide or Dipel) are a biological control. Covering plants with row covers often keeps them away, but it is too late at this point.

I don't know if cabbage loopers like Artichokes, but they would certainly go for Brussels Sprouts, Pak Choi and Chinese Cabbage. There are a variety of caterpillars that eat artichokes and members of the cabbage family. Kevin's advice on Bt above remains valid for all of them. Especially when the caterpillars are young. I usually don't worry much about Painted Lady caterpillars (as on artichokes). They are typically found at the base of a leaf, under a web. The damage you have looks like it came from something else. There are some big grasshoppers out now, too. They could cause damage like that seen on your artichoke. Bt won't work on them.

Greenthumbz, those are gorgeous pics! I've heard that there are a couple of trees that are not native to North America but are used by significant numbers of native insects. 1) Malus/Crabapples - native, hybrid, or exotic, Douglas Tallamy's book stated that the leaf chemistry is so similar that North american insects will use all species. This certainly bears true in my experience. I've got lots of crabs, a few specimens and a crazy wild thicket full of them in back,and they are bird magnets, not just for the fruits in the fall but for the nectar and insects in spring and summer. 2) Picea abies/Norway spruce - don't have any personal experience, but was told this by an ornithology student at Cornell who was doing a study on the subject

Kimmsr, this is an insect that feeds in large communities in one localized area. The removal of one branch may result in getting rid of several hundred larvae in one fell swoop, without the use of any chemicals at all. The removal of one or two branches may result in the preservation of this season's foliage. Why on Earth do anything else? Please note that spraying with Bt should be a last resort practice, just as with any other pesticide. Resistance to Bt has shown up all over the world, largely due to agricultural use of Bt, but homeowners contribute to the problem, as well. There are millions of people in this country alone that foster butterfly and moth habitats, something worth thinking about. The indiscriminate use of Bt-kurstaki products isn't acceptable, especially if there are other measures available. Is Bt-k a valuable and useful product? Absolutely, when used with care. Right place, right reason, right product. In this particular situation, with these particular insects, Bt-k is not a good fit. Moccasinlanding, can I assume that you are talking about River Birch, since you live in the South? They are a pretty little tree, but 'can' be a real insect magnet. Even in a native setting, this is the case. Aphids love River Birch. Landscape planted R. Birch are probably more susceptible to problems as there might be excess fertilization, irrigation, compaction, or other factors that can contribute to a plant's susceptibility. You'll be lucky if you can keep the population at bay with strong sprays of water or insecticidal soap (you did say it was a young tree, right?). This winter, however, after the leaves have dropped, you can begin with some applications of dormant or other horticultural oil. Spray all along the branches and trunk, and try to get into the nooks and crannies where those eggs are hidden. I'd spray three or four times, up until the time of bud break. You'll go a long way in breaking the aphid cycle. Have you seen any scale insects on this plant? ;-) You might as well take a good look!