Carnivorous Plants: Venus Flytrap and Pitcher Plant

Carnivorous Plants

Thomas Givnish’s Definition of Carnivorous Plants

First, carnivorous plants must be able to absorb nutrients from dead animals, thereby benefitting growth, survival, and reproduction. Second, carnivorous plants must have one or more certain adaptations for prey capture, attraction, or digestion (Givnish, 2018).

                

                 Pitcher Plant (Nepenthes)                                                   Venus Flytrap (Dionaea muscipula)                                           

Pitcher Plants (Nepenthes)

Physical Description

The pitcher plant resembles a vase, trumpet, pitcher-like structure and has a large leaf that folds to create a fluid-filled trap. It is heavily veined and has flaring leaves lined with downward-pointing bristles to trap prey inside. The grooved lip (peristome) at the top of the plant is purple-red and has white spots. This lid appears to be derived from a leaf tip (Givnish, 2018). The majority of the plant has green coloring, but it progressively gets more reddish-purple towards the top (Britannica).

                

Habitat and Climate

The best habitats for pitcher plants vary depending on whether they are American or tropical pitcher plants. American pitcher plants grow in southern Canada and the southeastern coastal plains of North America. They typically grow in nutrient-poor soil and wetlands like swamps, bogs, marshes, and fens. In contrast, tropical pitcher plants grow in northern Australia, Southeast Asia, southern China, India, and Madagascar. These pitcher plants typically grow near bodies of water, including lake edges, riverbanks, and springs (Akron Zoo). Growing in rainy, wet areas provides abundant fluid to fill the pitchers of Nepenthes. The nutrient-poor soil pitcher plants commonly grow in has a minimal supply of nitrogen and other nutrients. Thus, the plant must counteract this deficiency by obtaining nitrogen, phosphorus, and other nutrients from the captured insects (Givnish, 2018).

                   

*Natural habitat range of Nepenthes globally            *Natural habitat range of Nepenthes in the United States

Diet

Pitcher plants most commonly eat ants, but also other insects like flies, wasps, moths, butterflies, beetles, slugs, and snails. Larger pitcher plants can eat small frogs, rodents, and lizards (Akron Zoo).

          

How Pitcher Plants Lure Prey In

Insects are attracted to nectaries around the pitcher’s rim (peristome). Once the insect is close enough, it slips on this rim or a zone of waxy crystals below the pitcher opening and nectaries. These crystals readily detach, causing insects to lose footing and fall into the narrow cylindrical pitcher. The insect then drowns and is digested in the pitcher fluid (Givnish, 2018). 

     

How Pitcher Plants Digest Prey

The self-generated “water pool” is the primary digestion method of pitcher plants. To digest prey, pitcher plants produce various hydrolytic enzymes, including proteases and nepenthesin (Buch, Franziska, et al.). Nepenthesin works similarly to protease pepsin (mammalian digestive enzymes), but it is more stable and operates best at higher acid levels (ICPS).

         

Endangerment

There are over 150 different types of pitcher plant species. Thirty-five of these species are currently listed as vulnerable or endangered, and ten are listed as critically endangered. This endangerment is due to overcollection and poaching for the rare plant trade, habitat destruction due to agriculture and human development, invasive species, herbicides, and drought caused by climate change (WWF). 

Venus Flytrap (Dionaea muscipula)

 

Physical Description

The “trap” of the Venus flytrap is composed of large 2 hinged lobes on the ends of each leaf. Several of these traps can grow on a single plant and the plants often grow in clusters. A hinge-like midrib connects the two lobes. The interior surface of these lobes is bright reddish-pink in color, while the exterior of the lobes and the rest of the plant are light green. The lack of chloroplasts in the pink interior is believed to help avoid an overload of photosynthesis (Givnish, 2018). Along the inside of each lobe are three trichomes, or hair-like structures, projecting outwards. These six trichomes act as trigger hairs and signal for the trap to close when made contact with. Digestive and nectar glands (not visible to the naked eye) are also present along the inside of the lobes. 

               

Habitat and Climate

The Venus flytrap is native to the coastal plains and subtropical bogs/wetlands of North and South Carolina. While the species is endemic to this small region, it has been artificially introduced to other states, like Florida and New Jersey, and is a popular houseplant around the world (Luken, 2005). 

This species of carnivorous plant thrives with ample exposure to sunlight and in moist soils. As such, they are found almost exclusively in sparse areas with little to no canopy cover (<10%) and few other plants (most non-carnivorous plants cannot survive in such harsh soil conditions). The soil in this region is highly acidic and has low levels of nitrogen and phosphorus, both of which are important nutrients in plant growth. The Venus flytrap uses its carnivory to supplement its diet and counteract this deficiency (Waller, 2016).                        

         

*natural habitat range of Dionaea muscipula (Dlouhy, 2006) (FWS)

Diet

Venus flytraps mostly consume crawling and some flying arthropods but have even been known to trap worms. Their most common prey include spiders, ants, flies, beetles, woodlice, grasshoppers, and moths (Ellison & Gotelli, 2009). 

Though flytraps are able to make sugars through photosynthesis, consuming insects supplements their diet with nitrogen and other nutrients needed to build enzymes and stimulate growth. 

             

How Venus Flytraps Lure & Trap Prey

When exposed to sunlight, flytraps secrete nectar and a variety of volatile organic compounds (VOCs), many of which are also found in fruit and flower scents. This blend of sweet scents attracts hungry arthropods to the surface of the flytrap where, if 2 more trigger hairs are touched within 20 seconds of each other, the plant’s lobes close to trap the unlucky prey (Kreuzwieser et. al, 2014). 

The Venus flytrap is one of the only carnivorous plants that utilize thigmonasty, which is a plant’s movement in response to being touched, to actively move to capture prey. Almost all other species of carnivorous plants, like the pitcher plant, are stationary/passive (NWF). When 2 or more hairs are touched, calcium ions on the interior of the lobes are released, allowing the cellulose in the surface’s cell walls to expand and initiate the trap closing. As such, a change in water potential is essential for a trap’s closing, as it allows for the calcium ions to be released. This is a rather quick process, as the trap fully closes within just one second of the trigger hairs being touched. A single trap on a plant can only close 4 or 5 times before they fall off, as its supply of cellulose to expand and initiate closing is limited (Givnish, 2018). 

           

How Venus Flytraps Digest Prey

As the trapped organism tries to escape, its movements further stimulate the trigger hairs causing the lobes to close tighter and tighter until the trap is completely closed. Once closed, the airtight chamber formed by the two lobes acts as the plant’s unofficial stomach. The plant hormone jasmonic acid activates the digestive glands on the inside surface of the lobes to secrete digestive enzymes into the chamber. These enzymes break down the trapped prey and the nutrients are absorbed by the plant.

Endangerment

Dionaea muscipula is classified as vulnerable on the IUCN’s Red List (Schnell et. al, IUCN). Estimates from 2019 reported around 302,000 individuals remaining in the wild in the species’ native habitat range. This is a drastic population decrease of 93% from the roughly 4.5 million individuals surveyed in 1979 (Waller, 2016). For this reason, there have been several petitions to add the venus flytrap to the endangered species list but none have been successful yet. 

The biggest threats to venus flytrap survival are habitat loss, forest fires, and poaching. Current habitat loss is driven by agricultural and road expansion, pollution, natural disasters, and more. Regular forest fires can actually benefit venus flytraps, as they keep other plants/trees from encroaching on them. However, as fires are becoming more frequent, entire groupings of flytraps are at risk if adequate amounts of seeds are not spread prior to the fire to ensure the next generation. Poaching is becoming more of an issue for this species, as individuals are harvested from wild habitats to be sold as house/greenhouse plants (Jennings & Rohr, 2011).

 

References

 

Pitcher Plant References

Givnish, Thomas. “The Evolution and Ecology of Carnivorous Plants.” PBS Wisconsin. Wednesday Nite @ the Lab, 12 Sept. 2018, Madison, Wisconsin, Wisconsin Public Television, https://pbswisconsin.org/watch/university-place/the-ecology-and-evolution-of-carnivorous-plants-dxxtsw/. Accessed 20 Apr. 2022.

“Pitcher Plant.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., https://www.britannica.com/plant/pitcher-plant.

“Pitcher Plants.” Akron Zoo, https://www.akronzoo.org/pitcher-plants#:~:text=Habitat,edges%2C%20river%20banks%20and%20springs.

“Carnivorous Plant Digestion and Nutrient Assimilation.” Carnivorous Plant Digestion and Nutrient Assimilation | ICPS, https://www.carnivorousplants.org/cp/carnivory/digestion.

Buch, Franziska, et al. “Nepenthesin Protease Activity Indicates Digestive Fluid Dynamics in Carnivorous Nepenthes Plants.” PLOS ONE, Public Library of Science, https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0118853.

“Tropical Pitcher Plants Are Beautiful but Deadly.” WWF, World Wildlife Fund, https://www.worldwildlife.org/magazine/issues/fall-2020/articles/tropical-pitcher-plants-are-beautiful-but-deadly.

 

Venus Flytrap References

Bemm, Felix; Becker, Dirk; Larisch, Christina; Kreuzer, Ines; Escalante-Perez, Maria; Schulze, 

Waltraud X.; Ankenbrand, Markus; Weyer, Anna-Lena Van de; Krol, Elzbieta; Al-Rasheid, Khaled A.; Mithöfer, Axel; Weber, Andreas P.; Schultz, Jörg; Hedrich, Rainer (4 May 2016). “Venus flytrap carnivorous lifestyle builds on herbivore defense strategies”. Genome Research. 26 (6): 812–825. doi:10.1101/gr.202200.115. ISSN 1088-9051. PMC 4889972. PMID 27197216.

Dlouhy, Petr “Distribution of Dionaea in World,” Masqžravé rostliny, (25 July 2006).

http://www.honda-e.com/A02_World%20Maps/WorldMap_Dionaea.htm

Ellison, DM; Gotelli, NJ. “Energetics and the evolution of carnivorous plants – Darwin’s ‘Most 

Wonderful plants in the world'”. Journal of Experimental Botany. 60 (1): 19–42. (2009). doi:10.1093/jxb/ern179

U.S. Fish & Wildlife Services “Dionaea muscipula.”

https://www.fws.gov/species/venus-fly-trap-dionaea-muscipula

Givnish, Thomas. “The Evolution and Ecology of Carnivorous Plants.” PBS Wisconsin. Wednesday Nite @ the Lab, 12 Sept. 2018, Madison, Wisconsin, Wisconsin Public Television, https://pbswisconsin.org/watch/university-place/the-ecology-and-evolution-of-carnivorous-plants-dxxtsw/

Jennings, David E.; Rohr, Jason R. (1 May 2011). “A review of the conservation threats to carnivorous plants”. Biological Conservation. Ecoregional-scale monitoring within conservation areas, in a rapidly changing climate. 144 (5): 1356–1363. doi:10.1016/j.biocon.2011.03.013

Kreuzwieser, et. al. “The Venus flytrap attracts insects by the release of volatile organic 

compounds,” Journal of Experimental Botany, Volume 65, Issue 2. (February 2014). Pages 755–766, https://doi.org/10.1093/jxb/ert455.

Luken, James O. “Habitats of Dionaea muscipula (Venus’ Fly Trap), Droseraceae, Associated 

with Carolina Bays,” Southeastern Naturalist 4(4), 573-584, (1 December 2005). https://doi.org/10.1656/1528-7092(2005)004[0573:HODMVF]2.0.CO;2

National Wildlife Federation (NWF). “Venus Flytrap” 

https://www.nwf.org/Educational-Resources/Wildlife-Guide/Plants-and-Fungi/Venus-Flytrap

Schnell, D., Catling, P., Folkerts, G., Frost, C., Gardner, R., <i>et al.</i>. 2000. Dionaea 

muscipula. The IUCN Red List of Threatened Species 2000: e.T39636A10253384. https://dx.doi.org/10.2305/IUCN.UK.2000.RLTS.T39636A10253384.en

Waller, Donald “Petition to list the Venus flytrap (Dionaea muscipula Ellis) as

Endangered under the 1973 Endangered Species Act”. USFWS. (21 October 2016). https://www.researchgate.net/publication/310766408

Photos in diet section: https://parotesite.blogspot.com/2021/07/how-venus-flytrap-eat-insects.html