After millions of years, why are carnivorous plants still so small?

Prey Size, Risk, and “Mama Bear” Limits

• Larger mobile animals can usually escape and badly damage traps (breaking stalks, tearing sacs, crushing leaves).
• Several reports of pitcher plants killing mice and even a monkey infant suggest small mammals are possible, but not reliable prey.
• Some argue larger prey would trigger protective behavior from parents (“Mama Bear barrier”), raising plant damage risk. Others note many predators already target juveniles, so this is not a decisive argument.

Nutrient Economics & Habitat Constraints

• Multiple comments align with the article: carnivory mainly supplements nitrogen (and sometimes phosphorus) in very poor, wet soils where growth is otherwise limited.
• One perspective: photosynthesis already supplies far more energy than meat could, so bigger traps give diminishing returns.
• Another detailed thread debates whether nitrogen or phosphorus is the key limiting nutrient in bogs/swamps; consensus in the thread: nitrogen is usually more limiting there, phosphorus less so.

Fungi, Roots, and Cultivation Observations

• Anecdote from a commercial Venus flytrap grower: in nutrient-rich soil, cloned plants quickly died from fungal root attack, suggesting they’ve lost costly antifungal defenses adapted to “food desert” soils.
• Others generalize with experiences of Madrone, mango, lychee, and houseplants: too much water and nutrients often lead to root rot. Hydroponics is described as prone to algae/mold unless thoroughly sanitized.
• Another commenter notes that most conventional plants depend on mycorrhizal fungi, unlike many carnivorous plants in extremely poor soils.

Broader and Borderline Carnivory

• Examples raised of “quasi-carnivorous” or fertilizer-exploiting plants: brambles trapping sheep, coconut trees killing with falling nuts, devil’s-claw trees whose sticky seeds kill birds, trees and pitcher plants that attract animals to defecate into or near them.
• Discussion on why there are few plant-on-plant predators points to the success of parasitic plants (like mistletoe) and the difficulty of evolving chewing/biting with rigid cell walls.

Evolutionary Constraints & Dead Ends

• One commenter models carnivory as many narrow, local fitness peaks: useful only under specific conditions and easily outcompeted elsewhere.
• Another points out that several carnivorous lineages have lost much of their chloroplast genomes; heavy reliance on animal nutrients can become an evolutionary dead end that limits future transitions back to “normal” large, fast-growing plant forms.

Perception, Fiction, and Anecdotes

• Several humorous references (Little Shop of Horrors, Triffids, Piranha Plants) contrast popular images of giant man-eating plants with the ecological reality.
• A personal story describes a tiny Venus flytrap that attracted so many flies it seemingly “overloaded” its environment, illustrating that small carnivorous plants can be extremely effective within their niche without ever needing to become large.