[b said:
Quote[/b] (JustLikeAPill @ Aug. 30 2004,10:17)]hmm... why do neps need protein at all? they don't have muscles...
That's a good question, and requires a bit of understanding of biochemistry.
All life on earth uses three basic building blocks, categorized as proteins (made up of amino acids), carbohydrates (made from sugars), and fats (lipids). These are obviously used to a greater or lesser extent depending on the type of life. However, they are present and necessary in all terrestrial life of which i'm aware. And here is the reason:
carbohydrates are used for (typically short term) energy storage and transport (ever hear of "low blood sugar"?) and structure (cellulose in plants). Lipids are used for cell and other membranes (think "skin" for separating cells and parts of cells). Proteins are used for the "machinery", like the "factories" that convert sunlight to chemical energy (photosynthesis) or convert chemical energy to mechanical energy (muscles). Obviously this is a simplification.
Anywho, carnivorous plants exhibit a classic tactic that could be called "resource exchange". They take a resource they have in excess and use it to obtain a resource they don't have. They use the abundant energy (sunlight), water, and carbon dioxide (from the air) to produce excess sugars, which they use for bait for insects. These insects are made up of (in part) protein, which provides the plants with nitrogen, phosphorous, and potassium, which are all scarce in their habitat. So the plants are trading their extra sugars for proteins. This is why people try to use high-protein foods for their carnivorous plants: protein is what the plants are unable to get from other sources.
As a side note, i don't believe that the enzymes in the plants attempt to capture energy from what they digest. They are simply trying to get at the raw resources. As mentioned, energy is not really a rare commodity in a healthy CP habitat.