Insectivorous plants are so called since the animals they ingest/digest belong to insects like arthropods.
Among the living creatures, eating habits may be considered as diverse as the creatures themselves. Interesting fact is that animals are either vegetarian, carnivorous or both. Plants, on the other hand, use mostly simple raw materials to meet their food needs and to manufacture food for others. To be true, most of the plants (and some other living entities like bacteria and algae) synthesize carbohydrates from carbon dioxide using solar energy and water employing green pigment i.e. chlorophyll. Solar energy is used mainly to break water into oxygen and hydrogen. The electrons thus generated go through a complex electron transport cycle resulting in production of a diversity of organic compounds; the end result being synthesis of carbohydrates. The later are termed as storage house of chemical energy. This energy is then used by most living organisms especially the animals to sustain the natural system of beings. Oxygen generated through photolysis of water is what living organisms use to respire and thus make use of chemical energy. Thus photosynthesis by chlorophyll containing plants and other organisms not only results in the production and storage of chemical energy but replenishes oxygen consumed during the process of respiration or the so-called metabolic activities. This is how an integrated system of life is sustained in nature.
Most members of the plant kingdom are autotrophs i.e. they synthesize their food themselves from simplest raw materials as mentioned above. However, there are no plants that could be termed vegetarians like animals including humans. In fact, humans are fast turning vegans (no food of animal origin) to show humility towards animals. Interestingly, there are plant types that are carnivorous i.e. they obtain some or most of their nutrition through trapping and digesting animals. Insectivorous plants are so called since the animals they ingest/digest belong to insects like arthropods. Charles Darwin wrote the first ever treatise on insectivorous plants in 1875.
The insectivorous plants may or may not have the ability to trap as well as digest the insects. In some cases, they trap and kill only while relying on other associates (e.g. bacteria that are reared within the traps for this purpose) to mineralize the prey and let the plant use part of the nutrients thus released. Most often it is amino acids and other nitrogen forms that are made use of from trapped and decaying prey. This is because, the habitats of carnivorous plants are generally deficient in this essential nutrient element. These habitats may be acidic bogs or rock outcroppings. In these habitats, the plants are exposed to extreme sunshine.
Over a dozen different genera with nearly six hundred species are known to attract, trap and feed on insects. The genera include: Sarracenia, Paepalanthus, Aldrovanda, Brocchinia, Catopsis, Cephalotus, Darlingtonia, Drosera, Drosophillum, Dionaea, Genlisea, Heliamphora, Pinguicula, Triphophyllum, and Utricularia.
Evolutionary history of insectivorous plants is not well understood because of the paucity of fossil remains. However, they appear to have evolved as a last resort to survive and sustain an ecological niche that is fairly unfavorable to most plants. Not only plant morphology but biochemistry and physiology (particularly the enzyme systems and production of mucilage) has been modified in a way to trap insects and feed on them. Morphologically, it is the leafy structures that are modified in a way to function as traps. In general, carnivorous plants are poor competitors, because they invest too heavily in structures that have no selective advantage in nutrient-rich habitats. They succeed only where other plants fail. Besides, carnivory would appear to be merely an adaptation and not a choice. Under conditions, unfavorable to carnivory, the plants generally get rid of some of the pertinent characteristics. This is because this feature is highly energy intensive and by nature the living beings are conservative in spending energy.
UC Botanical Garden in the United States maintains a good collection of carnivorous plants. The author visited Botanical garden in 2014 and has opted to share some of the photographs taken then and to present some interesting information on these plants. The plants are indeed very colorful and attractive for all life types (including humans), what to say of those willing to be trapped and assimilated/annihilated.