Monarch larvae, especially 1st instars, are highly selective of the parts of the leaves that they ingest. We used direct observation of feeding, observation of feeding sites, determining by difference which specific tissues that they were removing from plants, and analysis of frass and orts to further explore the specificity of feeding on natural hosts plants. We found that the larvae avoid the vascular bundles, which include the laticifer networks that contain latex and defensive chemicals. We found also that the larvae will sometimes chew portions of the leaf that they fail to ingest, leaving partially chewed orts. The larvae ingest nutrient-rich palisade and spongy mesophyll cells with some epidermal cells. The feeding strategy of the monarch larvae is discussed in the context of developing an artificial diet for this species.