Snake heads are broadly classified into diamond-shaped and spoon-shaped. Snakes with diamond-shaped heads are dreaded because people associate them with venom. However, not every snake with a diamond head is poisonous. 

Diamond-shaped heads can appear on both venomous and non-venomous snakes. Some of the most well-known snakes with diamond-shaped heads include copperheads, rattlesnakes, and water moccasins. Non-venomous snakes with diamond-shaped heads include pythons and various water snakes.

In the rest of the article, I will comprehensively analyze common venomous and non-venomous snakes with diamond-shaped heads. This way, you can identify a snake more accurately and possibly protect yourself if you encounter one. 

Venomous Snakes With Diamond-Shaped Heads

Nearly all venomous snakes have diamond-shaped heads, but not all snakes with diamond-shaped heads are venomous. Therefore, I don’t recommend judging whether a snake is poisonous solely based on its head shape. Habitat, color patterns, and size are other traits to be considered.

All venomous snakes with diamond heads in America belong to the Viperidae (viper) family, except the coral snakes, which belong to the cobra family.

According to Live Science, the vipers include the following:

• Pit vipers (rattlesnakes, copper heads, and water moccasins)
• Adders
• The Gaboon viper
• Green viper
• Horned vipers

Vipers are known for large venom glands that stretch to the back of the upper jaw, which further contributes to a broad head. This head thus looks more like a prism from the front. 

Well-known poisonous snakes with diamond heads in America include the following:

• Western rattlesnake
• Western diamond-backed rattlesnake
• The eastern copperhead
• The northern cottonmouth
• The timber rattlesnake
• The prairie rattlesnake
• The sidewinder
• The western massasauga
• The red diamond rattlesnake
• The Mojave rattlesnake
• The cottonmouth
• Eastern coral snake
• Scarlet king snake
• Texas coral snake

All these snakes are highly venomous with the potential to kill. 

Non-Venomous Snakes With Diamond-Shaped Heads

Scientists have, however, established that some harmless non-venomous snakes can squish their heads to mimic the diamond shape. This adaptive technique makes these harmless snakes appear more dangerous. This way, head triangulation acts as a defense against aggression and attack.

The flattening of the head to triangulate is most common with colubrids. Though colubrids carry venom, this venom is considered unharmful to humans and most mammals. 

The following are the most common non-venomous snakes with diamond-shaped heads.

• Pythons and boids (boas) are the largest colubrids with diamond-shaped heads. These mega constrictors rely on muscle power to kill their prey. 
• Water snakes are another category of non-venomous snakes that have diamond heads. These snakes feed exclusively on fish and live near water. The most common species are the southern and diamond-backed water snakes, which are non-aggressive and flee when disturbed. The harmless bite is used as a last resort. 
• Corn snakes, common in Southeast US territories, also mimic the diamond head of the venomous snakes to appear more dangerous. They are common in corn fields and corn stores, where they prey on rodents.
• Their diamond-shaped heads make rat snakes look scary, but they are non-venomous and harmless to humans. These snakes vary in colors from black to olive and are mid-sized snakes, sometimes growing as long as five feet (1.52 meters).
• Garter snakes are a class of aquatic snakes. Their heads are often described as triangular or diamond-shaped. However, these heads are narrower than what you find in their venomous counterparts.
• Gopher snakes are harmless jungle snakes, but many people fear them. For some people, this fear is just because they’re snakes. However, other people fear them because their heads are diamond-shaped, and they erroneously think they are poisonous. 

Final Thoughts

Head shape alone cannot accurately determine whether a snake is venomous. Though most snakes with diamond-shaped heads are venomous, there are also many non-venomous diamond-shaped snakes. 

I recommend that you back off when you meet a snake, regardless of the shape of its head. A bite from a venomous snake can be fatal, and a bite from a non-venomous one can still hurt due to tissue damage caused by the fangs.