The Venus fly trap, Dionaea muscipula, is a carnivorous plant native exclusively to the wetlands of North and South Carolina. While it gains energy through photosynthesis, it captures prey for nutrient supplementation. Growing in boggy soil naturally poor in minerals, the plant acquires scarce nutrients like nitrogen and phosphorus by digesting small invertebrates. Its specialized, leaf-based traps are designed to actively lure, capture, and digest prey.
The Luring Strategy
The Venus fly trap definitively attracts bugs using a sophisticated strategy involving both visual and chemical cues. Visually, the inner surface of the trap lobes is often marked with deep red coloration, mimicking ripe fruits or flowers that insects associate with food. Insects are further drawn by a chemical bait released from glands along the trap’s edges. This secretion is a sweet, sticky nectar, and the plant also emits volatile organic compounds (VOCs) that create a subtle, fruity scent. This combination encourages the insect to land and explore the trap surface.
Which Insects are Targeted
The Venus fly trap’s diet favors insects that crawl or are small enough to be fully contained within the trap. Field studies show the diet is composed primarily of crawling arthropods. Ants make up approximately 33% of its prey, spiders account for 30%, and beetles and grasshoppers each comprise about 10%.
Prey Size Limitations
The trap’s physical dimensions impose a natural limitation on prey size. If an insect is too large, the lobes cannot fully seal, potentially causing the trap to decay. Conversely, insects that are too small may escape through the marginal spines or fail to trigger the closure mechanism. Due to the plant’s low-to-the-ground nature, it is generally not a significant predator of large, high-flying pollinators.
From Attraction to Capture
The actual capture mechanism is a rapid, mechanical process distinct from the initial luring phase. On the inner surface of each trap lobe are three to six fine, hair-like structures known as trigger hairs. These highly sensitive mechanoreceptors detect the presence and movement of potential prey.
The Two-Touch Rule
To prevent the plant from wasting energy on false alarms, such as falling debris, the “two-touch rule” is in place. The trap only springs shut if two separate trigger hairs are touched in succession, or one hair is touched twice, within approximately 20 seconds. This mechanical stimulus generates an electrical signal, known as an action potential, which travels across the trap’s surface.
The electrical signal causes a sudden change in turgor pressure within specialized cells along the trap’s midrib. The rapid redistribution of water releases the stored tension holding the lobes open, causing the trap to snap shut in a fraction of a second. As the trap closes, the stiff marginal spines interlock to form a cage, successfully caging the prey inside.
Nutritional Gain
Once the trap closes, the plant must confirm the presence of live prey before expending energy on digestion. The continued struggles of the captured insect stimulate the trigger hairs further, signaling the plant to prepare the meal. It takes approximately five distinct touches to fully initiate the production and secretion of digestive fluids.
The sealed trap effectively becomes a temporary stomach. The plant begins secreting a cocktail of acidic digestive enzymes, including chitinases and proteolytic enzymes, which break down the insect’s soft tissues. These enzymes dissolve everything except the hard, outer exoskeleton, which is composed of indigestible chitin.
Glands lining the inner surface of the trap then absorb the essential nutrients released from the dissolved insect. The primary compounds absorbed are nitrogen and phosphorus, necessary for the plant’s growth and development. The entire digestion process typically takes between three and ten days, after which the trap reopens, leaving behind the dried remains of the prey.