| 1 | Tiger rattlesnake |
The most toxic rattlesnake in the world, edging out the South American rattlesnake (Crotalus durissus). The latter has an LD50 rating of 0.17mg while the tiger rattlesnake reaches 0.06mg. To top it off, this is a rare rattlesnake with neurotoxic venom, alongside muscle-attacking myotoxins. Its venom is also among the simplest, with only 15 genes driving the production of toxins, while still managing to be utterly deadly.
Tiger rattlesnakes live in the Sonoran desert of Arizona and northern Mexico. Rather than forests, they prefer open areas, including short grasslands, rocky canyons, bajadas, and dry foothills – the kind of landscape featured in hundreds of Westerns.
Another special feature of tiger rattlesnakes is their small head, the smallest of all rattlesnakes. They use this to probe in rock crevices for prey, before seizing them with their hollow fangs. Their staple meals include pocket mice and kangaroo rats, and their rattle is also particularly small.
Recently, a completely new population of tiger rattlesnake was discovered in the southern Peloncillo mountains of Arizona. After all this time, there’s still mystery within the borders of the US.
| 2 | Sidewinder rattlesnake |
The most desert-adapted rattlesnake worldwide. This is named for its signature locomotion style: travelling sideways with only two tiny points on its head and tail, writhing constantly so that only the tiniest amount of body is touching the scorching sand dunes at any one time. Sidewinders don’t just live in arid semi-desert, but white sand dunes, including the Mesquite Flat Sand Dunes of Death Valley.
Sidewinders are instantly recognisable both for their sand-coloured scales (for camouflage), and horns above their eye. Rather than piercing enemies, it’s believed that these horns shield their eyes from sunlight. With its parched landscapes, this rattlesnake relies more on lizards than some, making up 50% of calories. The banded gecko is a favourite, and among mammals they enjoy kangaroo rats.
Sidewinder rattlesnakes occupy four states: California, Nevada, Arizona, and southwestern Utah. Being so remote, bites hardly ever happen, but can be severe if they do. A 56 year old man bitten in 2014 suffered extreme nausea, a burning pain up to the groin, and unsteady feet lasting for 3 days. This man managed to be bitten on the foot despite the precaution of tough leather boots.
| 3 | Rock rattlesnake |
The greyest rattlesnake in the southern US neighbourhood. There’s 4 subspecies, with the banded rock rattlesnake having thick stripes, but the grey base always remains. The grey colour is to blend with their main habitat: rocky outcrop and scree slopes. They also appear on rocky streambeds, and rocky slopes within montane conifer forests. Rock rattlesnakes lives remotely, and bites are very rare. The main peril is to hikers, scrabbling over isolated rocky slopes on a glorious day out. This rattlesnake can rest on its slopes for hours, soaking up the warm sunlight.
Rock rattlesnakes inhabit southwest Texas, southern New Mexico, and far southeast Arizona. They’re one of the shorter local rattlesnakes, averaging at 60-70cm. Males are longer than females, and sometimes push to 80cm.
With such superb camouflage, the rock rattlesnake has no need for all out aggression. But if they do bite, the symptoms include pain, nausea, soft tissue swelling, and haemorrhaging. This is a rare rattlesnake to favour reptiles, which made up 55.4% of their diet according to a 2009 study.
| 4 | Southwestern speckled rattlesnake |
This is another rock-loving rattlesnake, but its range doesn’t overlap with the rock rattlesnake further east. With no competitors, it seems to have claimed the rocky habitat niche for its own. Southwestern speckled rattlesnakes live in western Arizona, Nevada, Utah and southern California. Unlike the red diamond rattlesnake they coexist with, they only rarely stray to scrubland or cactus country, much preferring rocky slopes or canyons.
Crotalus pyrrhus is also called the bleached rattlesnake or pallid rattlesnake, and on a gravelly slope their camouflage can be supreme. This is a common rattlesnake, not endangered at all, and they’re one of the longer southern rattlesnakes at up to 137.5cm. They have the usual rattlesnake reliance on mammals, at 80.8% of their diet in one study. At 39.4% of prey, they were particularly reliant on terrestrial squirrels.
Officially, the southwestern speckled rattlesnake has a relatively weak venom, at LD50 2.7mg, versus 0.18mg for the Mojave rattlesnake. However, a patient bitten in Phoenix Mountains, Maricopa County ended up having part of his middle finger amputated.
| 5 | Red diamond rattlesnake |
The most mammal-dependent rattlesnake of the southern USA. A study found that red diamond rattlesnakes derive 91.6% of their prey from mammals, particularly rodents, with 7.5% coming from reptiles and 0.9% from birds.
Red diamond rattlesnakes (Crotalus ruber) appear in many habitats, including deserts, pine oak woods, tropical semi-deciduous forests. However, their favourites are easily scrubland, particularly scrubland of sage and chaparral. The soils here are perfect for their rodent prey to burrow in. Crotalus ruber is a semi-ambush predator, but not quite. They don’t wait in a single spot and hope for prey to traipse past, but actively search for burrows and well-trodden rodent trails. Then they’ll wait in ambush outside those spots for prey to appear.
In the US, Crotalus ruber resides solely in the south of California. Then it extends southwards deep in Mexico, along the Baja California peninsular. Consequently, it doesn’t overlap with most rattlesnakes on our list, except the southwest Speckled rattlesnake. This rattlesnake is common in the cooler coastal zones of southern California, and also the mountains.
| 6 | Black-tailed rattlesnake |
This timid species is the longest of our list, with the maximum size on record being 152.4cm. However, it’s most obviously recognisable by its jet black tail. There’s also a black band between its eyes, and black strips from its eyes to the corner of its mouth. Crotalus molosuss resides in Arizona, New Mexico and southwest Texas. This form is the northern subspecies (crotalus molosuss molosuss), with Mexico having two subspecies.
Black-tailed rattlesnakes have one of the weakest venoms. When a 12 year old girl was bitten on the foot in her backyard, she experienced swelling and pain which eventually progressed to above her knee. However, there were no systemic symptoms, not even vomiting or dizziness. There was no necrosis or blisters; the worst was a persistent numbness in her foot.
Black-tailed rattlesnakes are reluctant to bite, and generally live in mountainous areas. These include rocky canyons, or high altitude pine forests, while at lowlands they sometimes inhabit semi-deserts. Crotalus molossus has a diet mostly consisting of small mammals, with lizards eaten occasionally.
| 7 | Ridge-nosed rattlesnake |
The sky island rattlesnake. This little known species lives solely in high mountain ranges surrounded on each side by desert, in remote places far from human settlements. These include the Santa Rita, Patagonia, and Huachuca Mountains of Arizona. There’s two subspecies in the US, the Arizona ridge-nosed rattlesnake, and the New Mexico ridge-nosed rattlesnake, which is severely endangered.
Within the mountains, their favourite spots are well-vegetated canyons, often with pine forests, perhaps ones that outlaws would have hidden in. With their brown background overlaid with thin white stripes, this is an easy rattlesnake to recognise. They’re a small rattlesnake at just 30-60cm, and consequently their fangs don’t spew out much venom, limiting the danger. When one 57 year old man was bitten on the hand, the worst symptom was swelling that extended halfway up the bicep. He fully recovered with 3 days. This rattlesnake’s first instinct when confronted is to crawl away rather than fight back viciously.
Crotalus willardi is another lizard-eater, getting 50.7% of its calories from reptiles (study). Only 12.7% was mammals, and 28.2% was birds. They also had the unusual prey of centipedes (8.2%).
| 8 | Mojave rattlesnake |
The other desert surfer, well adapted to scorching barren wastes. In the USA, Mojave rattlesnakes are found in Texas, Nevada, New Mexico, Arizona, California, and extreme southwest Utah. They’re less heat-adapted than sidewinders, but favour semi-deserts and short, barren grassland with wide open views stretching out ahead. Mojave rattlesnakes average at 100cm, and the record was 137.3cm. Their diet is biased in favour of mammals, but less overwhelmingly than red diamond rattlesnakes. A study found that 19 contained mammal remains, and 15 contained reptile remains. One of the reptiles was a western whiptail lizard.
This rattlesnake has two venom types, A and B. Venom A is rich in Mojave toxin, a neurotoxin which causes trouble breathing and vision problems. Venom B is confined to a small area of Arizona, and is mostly haemorrhagic and proteolytic, properties which venom A lacks. This species has one of the strongest rattlesnake venoms of all, potentially killing via respiratory failure. Neurotoxins are uncommon in rattlesnakes; the tiger rattlesnake is another rare one to contain them. Fortunately, deaths are rare, as the standard US antivenin CroFab is made using Mojave rattlesnake venom A.
| 9 | Arizona black rattlesnake |
This endangered rattlesnake stands out by being mostly black, with thin white bands crossing though. They also live almost exclusively at high elevations, in “sky island” forested regions within national parks. They appear in rugged lands such as Coronado National Forest, Tonto NF, and Prescott NF, preferring cooler and moister habitats compared to most rattlesnakes. They also live in far western New Mexico, in the Gila Wilderness zone. Crotalus cerberus is relatively long for our list, with the maximum confirmed size being 129.1cm.
Arizona black rattlesnakes have a mostly proteolytic venom, causing local damage to skin. One study examined 7 western rattlesnake species, including the prairie rattlesnake. The Arizona black rattlesnake had the highest quantities of metalloproteases, which cleave amino acids to dissolve proteins into rubble (they’re also involved in natural human skin recycling). Yet its venom was the weakest of the 7 towards mice, with an LD50 score of 5.4mg vs 0.36mg for midget faded rattlesnakes (the strongest), and 1.55mg for prairie rattlesnakes.
Restricted to two states, this is the most endangered rattlesnake of our list, as its forested National Parks are steadily degraded. A 2016 study put them on an extinction trajectory.
| 10 | Twin-spotted rattlesnake |
This 50-60cm rattlesnake mostly lives in Mexico, with only a tiny range in the USA. It lives solely in Arizona, and even then, only within the mountains of Chiricahua, Huachuca, Pinaleno, Dos Cabezas, and Santa Rita. Despite this rarity, they can be common in good habitat, with several appearing in a few square metres.
The twin-spotted rattlesnake reaches high altitudes of 2900 metres, and is the most reptile-loving rattlesnake of the southern USA. When tested in Arizona’s Chiricahua Mountains, their diet consisted of 74% reptiles. Its favourite prey of all is Yarrow’s spiny lizard, which is fighting back by evolving venom resistance. On their mountains, they’re at home in pine-oak woodland, coniferous woods, grassy and brushy areas, and rocky slopes alike. In forests they like to hang out in tree stumps.
This is a short species, with a maximum recorded length of 66cm, less than 50% of the black-tailed’s record. It has a triangular head, and its colours are non-flashy, consisting of beige, light brown or grey patterns. Unlike the Arizona black rattlesnake, this species isn’t endangered; the population was perfectly stable when assessed in 2007.