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Peppers are Spicy to Attract Birds and Discourage Mammals

May 7, 2011 No Comments

Have you ever wondered why plants and foods such as jalapenos and chili peppers (pictured above) are so spicy hot? It all has to do with a single molecule called Capsaicin.

Capsaicin is a secondary metabolite, a molecule that plants use for defense. These special compounds are called secondary metabolites, and they help plants defend themselves against herbivores, insects, germs, and competitors. The compounds are referred to as “secondary” because the plant technically can survive without them, but the compounds do increase the plant’s survival and help it to compete better with other species. Some plants use secondary metabolites for reasons other than defense, such as using them to become a certain color or to attract insects. We (humans) use these compounds for all sorts of things!

Examples of plant secondary metabolites:

  • Alkaloids: Plants use these as anti-microbials and neurotoxins. Humans use them as drugs such as Morphine, Caffeine, and Cocaine.
  • Phenolics: Plants use these as anti-microbials, and digestion inhibitors. Humans use them for a variety of drugs and even use them for flavors and scents such as cinnamon and vanilla.
  • Glucosinolates: Plants have them because they are slightly toxic. Humans use them as food and flavor (horseradish, mustard).

How Capsaicin works: The compound in peppers, Capsaicin, tricks an animal’s nerve cells into thinking they are exposed to heat (which is why it feels like your mouth is on fire when you eat a jalapeno pepper). However, the chemical doesn’t actually harm your nerve cells!

This is a picture of what the Capsaicin molecule looks like:

Why do certain plants contain Capsaicin? There are two reasons:

  1. Mammals and insects are sensitive to Capsaicin, but birds are not. Is it possible that the plants have evolved this chemical to benefit themselves? Mammals and insects are not very good seed dispersers. For example, a rodent that eats a pepper seed will eat it by tearing the seed into pieces. Therefore, after the seed passes through the rodent’s digestive system, the seed is less likely able to grow. Also, the mammal will most likely drop the seed near the parent plant or in an underground burrow (where the seed won’t be able to germinate). In contrast, birds swallow seeds whole and fly farther distances, meaning the seed is more likely to grow after going through a bird’s digestive system and it will travel further away from the parent plant. In terms of survival of the plant species, birds are a much better option! This could explain why capsaicin is good for plants: it keeps the mammals and insects away but encourages birds.
  2. Capsaicin is an anti-fungal compound, meaning it reduces and limits how much damage fungi can do to the plant’s fruit (the peppers).

Humans use Capsaicin in many ways. The most obvious way is that we eat the fruit of the plants and use them as spices. We also make pepper spray from capsaicin, and the squirrel deterrent in bird seed is capsaicin.

Why do humans eat Capsaicin? All through this article I’ve explained that mammals don’t like eating hot and spicy Capsaicin. But aren’t we mammals? Yes. Then why do we still eat the stuff? The biological reasons we eat peppers are: we eat capsaicin for its anti-microbial properties, it stimulates the parasympathetic nervous system (sweating, lowered body temperature, etc), and it stimulates Opioid production in the brain. We probably eat spicy foods for psychologic reasons too (humans receive pleasure from negative experiences that have no real danger).

The Absolute, Most Spiciest Pepper!!! The spiciest pepper in the world (that is naturally grown) is the ghost pepper, also known as the Bhut Jolokia Chili Pepper. Spiciness is measured on a very specific, measurable scale with units of SHU (Scoville Heat Units). The ghost pepper has a spiciness of 1,000,000 + SHU!!! For comparison, here are some common peppers and their level of spiciness:

  • sweet bell pepper: 0 SHU
  • paprika: 250 – 1000 SHU
  • jalapeno: 2,500 – 8,000 SHU
  • Serrano: 5,000 – 23,000 SHU
  • Tabasco: 30,000 – 50,000 SHU
  • habanero: 100,000 – 350,000 SHU
  • note: there are three other types of pepper spicier than the ghost pepper, but they are not natural; they’re grown in laboratories and factories.

FINAL NOTES: If you managed to read this entire post, then congrats! I really hope that you found this interesting and enjoyed reading. I certainly found this topic very interesting! I learned most of the information in a class I’m taking this semester in college, but I added a bit more information that I found.

If you’re interested, take a look at this video, which shows a man on a tv show taking the “Four-Horsemen Burger Challenge,” in which he attempts to eat a hamburger with several different types of spicy peppers, including the spiciest in the world: the ghost pepper! The man has to wear gloves in order to touch his food because it is soooo hot!

disclaimer for the four horsemen burger

Man Vs. Food: The Four Horsemen Burger Challenge

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