Why Do Cacti Have Spines?

A cactus has spines for several different reasons, such as reproduction, shading, water regulation, cooling, and protection. Learn about species from North America, including Echinocereus, Ferocactus, Mammillaria, Opuntia engelmannii, Saguaro, and Triangle cactus

We’ve all seen the pictures of the tall cacti that populate the deserts of the American West. The spines that we see Wile E. Coyote picking from his backside aren’t just there to protect the plant. A cactus spine has several functions.

Why do cacti have spines? A cactus has spines for several different reasons. They are:

  • Reproduction
  • Shade
  • Water Regulation
  • Cooling
  • Protection

The spines are one of the many amazing things that cacti produce. If you are skeptical about the plant or are looking for something to make your desert garden, keep on reading and learn some fantastic properties the cactus has to offer.

What Function Do Cactus Spines Have?

When it comes to all the things that cactus spines can do, you would be shocked. Everyone knows that they keep predators at bay, but did you know they also aid in reproduction? The main functions of cactus spines are:

Top view image of cactus.
Cactus spines bear multiple functions, including reproduction, shading, water regulation, cooling, and protection


Life in the desert is a tough go. The animals that live there make a hard life with little water and even less food. One of the favorite foods of desert animals is the cactus. Animals like the hummingbird and bats are the primary pollinators of the plant. Its skin contains large amounts of water as well. These animals do this at their own peril, because some tiny cacti material can remain lodged in their skin and lead to serious illness or death.

Golden barrel cactus closeup image.
Its skin contains large amounts of water as well.

The spines do a fantastic thing when they are encountered with one of these animals. When they go in for a nice juicy bite of cactus juice, the needles will pierce their skin and remove from the cactus. What they do next is amazing and perpetuates the species. When the barb detaches from the plant, it takes a tiny bit of cactus material with it. As the animal moves, the spine will dislodge and begin to take root where it lands.


The temps in the desert can reach as high as 130 degrees Fahrenheit. All the plants and animals search for precious shade, which could mean the difference between life and death. An unexpected place that a cactus gets shade is from its spines. As the sun moves, a tiny sliver of shadow protects the essential parts of the stem or trunk.

A cactus spine is tiny and isn’t a place you would think the shade would be abundant. The good thing is that a cactus can have thousands of them, and when they are all closely located, they do an excellent job of being shady. The larger the surface of the cactus, the more spines there will be.

Cacti in a pot.
Cacti get shade from their own spines, preventing the essential parts of the plant from drying out

The giant Saguaro cactus has longer prongs that won’t reach maturity until the plant is over 100 years old. These prongs have a tiny forest of smaller spines at their base that protect the genetic material. This critical spot at the bottom of each prong provides the shade that allows the plant skin to retain water.

You wouldn’t think it, but some cacti have a root system that can spread out over 100ft in search of water. The arms and spines of larger plants will cast shade on the ground that will keep the sun from eroding its waterbed.

Water Regulation

If you live where most cacti live, you would understand how important water can be. A desert receives less than 10 inches of rain a year. That means that if it does rain, it is infrequent, and every drop must be utilized for survival.

Spines on a cactus are inactive, which means that they do not absorb water. What they do is provide an area for tiny particles to be collected and funneled down to the wet skin beneath. Their surface area means that a high percentage of water that does hit the plant gets where it needs to go.

Different kinds of cactus.
Spines keep a cactus hydrated through collecting tiny water particles and transferring them to the plant skin


The spines on a cactus keep cooler air closer to the skin of the plant. The temperature is kept cooler, but not free from the heat. It works by making sure that there aren’t large drops or rises in the skin temp. The heat range in the desert can swing more than 70 degrees once the sun goes down. At night, the cactus soaks up cool air and the morning sun turns it into water vapor. Which the plant then uses as a cooling agent or for a drink.

Spines on the cactus act like an extra layer of clothing by shedding or collecting heat. The temps in the desert have a high fall off in degree from the daylight until the moon is up. A shift in temperature could be damaging the plant or even kill it.

Glochids, the tiny hair-like spines at the base of prongs, trap water moisture as it splashes off the large leaves. This splashing creates a far more wet environment that will promote the growth of lush plant skin.


The legendary sharpness of cactus spines doesn’t need much of an explanation. They provide ample protection from all the plant-eating animals of the desert. That doesn’t mean that animals aren’t relying on the fruit of the cactus. Smaller animals, like mice and rodents, disregard the spines and eat the fruit regardless.

What you might not see are some nasty tiny fibers that could cause infection if not removed. Spines are barbed like fishhooks. When one of them enters the skin of an animal, or you, it creates more debris if it is removed. The remnants aren’t quickly taken care of and will cause a nasty infection if they remain in the skin.

A reptile with cactus behind.
The sharpness of spines protects the cactus from plant-eating animals, especially in the desert

What Is A Cactus Spine?

If you were to call the spines on a cactus prickles or thorns, you’d be wrong. When it comes to thorns, they are just a kind of branch for a smaller plant. A spine is a mutated leaf bud. It grows from the areoles on the surface of the cactus.

When it is mature, a spine shares little or nothing in common with a leaf. Think of it as a fingernail. It grows new material only at the base, and everything else has dead cells. When you talk about spines, it would be a mistake not to also talk about glochids.


Growing closer to the surface of the areole are tiny hair-like spines called glochids. The average spine can pierce the skin and lodge deep into your flesh. However, once they are removed, they can be treated like any other wound.

When it comes to glochids, you might not be that lucky. Not only can they pierce your skin, but they will embed themselves so that they cannot be removed. The size of them makes it an impossible task to remove one. Things to look for when treating a possible glochid wound are:

Sabra dermatitis (Prickly-pear contact dermatitis)

Sabra dermatitis is an illness that is associated with glochids from certain fruits. The pickers will have problems with scabies like outbreak that they can’t remember receiving the wound. Sabra can also be caught when the glochids of certain fruits become airborne. Finding tiny cactus spines in your throat sounds like an unpleasant experience.

Once a person has been diagnosed with sabra dermatitis, picking the fruit must come to an end. An ointment or salve, maybe a tiny dosage of antibiotic, is the best way to treat dermatitis. Once the medicines have run their course, around a week, you should be able to return to your normal routine.

A Prickly pear cactus bearing fruits.
Glochids from some cactus fruits can lead to Sabra Dermatitis, which is an irritant contact dermatitis.

Removing Glochidia

If you see pustules and swelling around an area there’s a good chance a tiny sliver of glochid remains. The barbs on the outside of the sliver will root the material there unless you take steps to remove it.

If a tiny sliver of a glochid remains in your skin, you could be in for a world of hurt. The most effective way to remove them is to do it the old fashioned way with tweezers. The tweezer is going to take time and might be painful. A newer approach is to wax them like you would body hair.

Place a bead of wax along the infected area, allow it to dry, and it is party time. This method will also be pretty painful, but much quicker and less effective. You could have to do it a few times to make sure that they are all removed.

The Cacti Of North America

The cactus is an interesting plant that evolved to become a stem succulent. That means that they have developed what was once leaves to process water taken inside the trunk of the cactus. Photosynthesis is the process that plants use to create food and oxygen. When the leaves of the cactus began to evolve out, the stem, or trunk, began to photosynthesize and store water. The root system also saves a decent amount of water, but most storage happens in the trunk.

The leaves have gone away over time to become the beloved spines of recent discussion. They are members of the family Cactaceae with almost 1800 subspecies of cactus. They come in a cast array of sizes and colors. A large portion of these types is found in the Americas from Patagonia to Northern Canada. The most common forms of cactus in North America are:

  1. Echinocereus
  2. Ferocactus
  3. Mammillaria
  4. Opuntia engelmanii
  5. Saguaro
  6. Coryphantha
  7. Triangle cactus

1. Echinocereus

This cactus is very prevalent in the Southwest, with about 70 species residing there. They are long cylinders that have some neat colored spines that can make some fantastic designs. A significant feature of the Echinocereus is its flowers. It has a bright red flower that can be eaten if needed. The flowers are also in bloom for much longer than their cousins.

People often choose this breed for its decorative feel. The skin color, combined with the spines coloration, will add much-needed variety to your garden. It requires a rocky and sunny environment to survive and will have a hard time with wet, cold climates.

2. Ferocactus

A Ferocactus in a pot.
A Ferocactus is a barrel-shaped cactus native to Southwest and Western parts of Mexico

A Ferocactus is a smaller barrel-shaped cactus that is low to the ground and usually forms in clusters. It starts like other cacti, as a long blade, but as they get older, they spread out by creating ribs. Ferocactus is native to the Southwest and Western parts of Mexico. It is a drier climate cactus. It has to have an arid climate but can withstand some severe drop of temps as well.

The incredible innovation of this type of plant is that it shifts to be closer to areas where water can pool or be stagnant. The root system will extend itself towards a constant water source. Also, the plant itself moves by increasing several ribs in the direction of the root system. These ribs extend the barrel shape of the cactus.

3. Mammillaria

A flowering Mammillaria.
Mammillaria can be found throughout the Caribbean as well as in certain parts of Northern South America

This plant is what most people call the pin-cushion cactus. It is the type of cactus that comes in tiny pots and is grown on your windowsill. Mammillaria is the most prevalent species of cactus with over 200 species in this family alone. They grow mostly in Mexico but can be found all over the Caribbean and parts of northern South America.

The explosion of the popularity in this cactus has made locking down all the naming nomenclature an intensive pursuit. For decades, plant nurseries named every cactus Mammillaria. Thereby negating any scientific opinion on the subject. Be cautious when purchasing any cactus that is labeled Mammillaria. If you are going to add a Mammillaria to your garden, be sure that it is the correct species. Not all have flowers, and some never leave the tiny pot stage.

4. Opuntia engelmannii

This cactus is better known by the name Texas Prickly-Pear. It is a long flat blade that has clusters of spines on its face. They are found in the Southwest US and Northern Mexico. That also can bloom with beautiful yellow flowers, which make a nice contrast with their blue-green skin. The blooms are fascinating in that they only live for one 8-hour period from April to May. Making them somewhat of an oddity to be watched as well as tended in the garden.

They are best known for growing in large clusters, some as large as 11 feet high. For generations, the prickly-pear that is produced has been a food staple for many indigenous people in the Southwest.

5. Saguaro

Saguaro is the type of cactus that is most often depicted in the media. It is a tall trunk, usually with a couple of branches. A saguaro can grow to be 40 feet tall and weigh 5000lbs. What makes this type of cactus grow so vast is the gigantic root system that it forms. A root system for a saguaro can grow up to 100 feet in every direction from the cactus base. That’s a tremendous amount of space. But, it could take them as long as 75 years to gain any real size.

After the first year of planting, they are still only 1/4in tall. They also need large amounts of water to reach this size. That is why the largest specimens are reported in Arizona, where they get more rain than their Mexican cousins. The largest Saguaro ever found was 78 feet tall. As large as an average pine tree.

A Saguaro Cactus.
Saguaro cactus

6. Coryphantha

One of the most exciting cacti in the Americas is coryphantha. This plant has a fantastic flower that can range from bright yellow to a deep purple. It grows from the top of the cactus, which makes it more unique than others. Another thing that makes it stick out is that it doesn’t have ribs, but tubercules. This plant is also well known for having a spine grouping that fans out like a large umbrella. It does great at providing shade, which is essential for these arid living plants. The coryphantha has two subgenera and over 50 sub-species.

7. Triangle cactus

It wouldn’t be a list without the most popular cactus in Florida! The home of several gators and snakes also houses one of the most amazing plants in the family. They are also found around the Caribbean and are distinguished by their columnar shape and protruding arms. The triangle cactus can grow to over 20 feet and in a much shorter lifespan than their brother, the Saguaro. They have a distinctive flower that encompasses all shades of white into a vibrant flower, which looks great in any desert garden.

Cactus as Food

Not only are the cacti of the desert an excellent place to search for water, but they are also a decent source of food. A unique way to tell if a cactus is good to eat is by the shape of the leaves. If they are oval-shaped and look like ping pong paddles, they should be good to eat. These types of cactus are called Nopales or Prickly Pear. The meat from the cactus is famous across the Americas and even some locations in Europe.

The texture of the plant is sticky with a middling crunch factor. They are usually canned or made into acitrones, which means they are just candied and stored in syrup. Preparation means that all spines, skin, and areolas are removed from the plant. Some prefer to eat the meat raw, while others will steam it like you would a normal veggie side. It is a versatile plant that can be added to almost any meal with surprising results.

Steamed cactus is one of those condiments that you find out west that blows your mind. It can be added to any meal with eggs or added to a taco. One of the most popular and tasty, sounding dishes comes from Mexico, where they pair it with spicy peppers and corn. A very palatable option is to throw the chunks into a tossed salad in place of cucumber. It will give the dish a refreshing flavor, not unlike guacamole.

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