In zoology, a palynivore is an herbivorous animal which selectively eats the nutrient-rich pollen produced by angiosperms and gymnosperms. Most true palynivores are insects or mites. The category in its strictest application includes essentially all bees, and a few different kinds of wasps, as pollen is often the only solid food consumed by all life stages in these insects (palynivorous mites and thrips typically feed on the liquid content of the pollen grains without actually consuming the exine). The list is expanded greatly if one takes into consideration species where either the larval or adult stage feeds on pollen, but not both; there are other wasps which are in this category, as well as many beetles, flies, butterflies, and moths. There is a vast array of different insects that will feed opportunistically on pollen, as will various birds, orb-weaving spiders and other nectarivores.