How Big Is an Eastern Diamondback? The Heaviest Rattlesnake

Typical length and weight of adults

The eastern diamondback rattlesnake is a heavy-bodied snake, much thicker than most North American species. Field guides give typical adult lengths of about 0.9–1.8 m (3–6 ft), with many adults in the 1.1–1.7 m (3.5–5.5 ft) range. One study of 74 adults (31 males and 43 females) found an average length of about 1.7 m (5.6 ft), although averages from other samples are lower.

Weight varies with length, body condition and the last meal. An average adult weighs roughly 2.3 kg (5 lb). In one group of nine captive snakes, weights ranged from 0.8 to 4.9 kg (1.8–10.8 lb). Few individuals pass about 5 kg (11 lb), although exceptional snakes can reach 6.7 kg (15 lb) or more.

Males are bigger than females

In many snake species females grow larger, because a bigger body can hold more eggs or young. Eastern diamondbacks are the opposite. Adult males grow longer and heavier than females, a pattern biologists call reverse sexual size dimorphism.

The likely reason is competition. During the mating season, male rattlesnakes wrestle in “combat dances,” rearing up and trying to push each other to the ground. Bigger males tend to win these contests and gain access to females, so natural selection favors large size in males.

The largest reliable records vs old claims

The figure most often repeated is a snake shot in 1946 that was reported at 2.4 m (7.8 ft) long and 15.4 kg (34 lb). Other sources list maximum lengths of 2.4 m (8 ft) and 2.5 m (8.25 ft). The problem is that none of these giants was kept as a measured museum specimen, so scientists cannot check them.

The great rattlesnake researcher Laurence Klauber was skeptical of 8-foot claims. In his classic book on rattlesnakes, he published a 1953 letter from E. Ross Allen, who ran a well-known reptile attraction in Florida. Allen said he had offered a reward of 100 dollars, later 200 dollars, for an 8-foot diamondback, dead or alive. He received several snakes in the 7-foot range, but nobody ever claimed the reward.

Allen also pointed out a common source of error: snake skins stretch. A skin measuring 2.4 m (8 ft) can come from a snake only about 1.8 m (6 ft) long, so tanned skins and photographs of hanging snakes exaggerate size. Photos taken with the snake held close to the camera make it look larger still.

Well-measured large snakes do turn up. A diamondback of about 2.2 m (7.3 ft) was found near St. Augustine, Florida, in 2009, showing that 7-foot snakes still exist, even if they are rare.

Why big diamondbacks are rarer today

Snakes keep growing slowly throughout life, so the largest individuals are usually the oldest. In the past, more diamondbacks reached a great age. Today, several pressures remove big adults before they can reach record size:

• Killing by people. Large rattlesnakes are the most noticeable and are often killed on sight.
• Skin and trophy collecting. Big snakes were favored for skins and for prizes at rattlesnake roundups, which removed the largest animals year after year.
• Roads. Big snakes move slowly across roads and are frequently run over.
• Habitat loss. The longleaf pine forests where diamondbacks grow up have shrunk to a small fraction of their original area, so fewer snakes survive long enough to get huge.

Food matters too. Diamondbacks that feed mainly on rabbits can grow faster and bulkier than those living on smaller rodents, so the biggest snakes come from healthy habitat with plenty of prey.

How big are newborns, and how fast do they grow?

Eastern diamondbacks give birth to live young, usually 7–15 per litter. Each newborn is about 30–36 cm (12–14 in) long and already big enough to swallow an adult mouse. Young snakes grow quickly in their first few years and shed their skin several times a year, adding a rattle segment each time.

Growth slows after maturity, which females reach at about 2–4 years old. From then on a snake may add only a little length each year, so a 6-foot diamondback is likely to be many years old.

Eastern vs western diamondback: which is bigger?

The eastern diamondback is bigger than its relative, the western diamondback rattlesnake. Western diamondbacks are commonly about 1.2 m (4 ft) long; snakes over 1.5 m (5 ft) are uncommon, and the largest reliable record is about 2.1 m (7 ft). Medium-sized westerns weigh about 1.2–2.7 kg (3–6 lb).

So while both can occasionally reach about 2 m (6.5 ft), the eastern species is longer on average and noticeably heavier and thicker. For a full side-by-side guide, see eastern vs western diamondback.

How does it compare with other big venomous snakes?

The eastern diamondback is the heaviest rattlesnake, but it is not the heaviest venomous snake in the world. The Gaboon viper of Africa is even bulkier for its length, and the king cobra of Asia, though much more slender, is far longer at up to about 5.5 m (18 ft). In the Americas, the bushmasters of Central and South America can be longer than diamondbacks and similar in weight.

Size also explains why the eastern diamondback is considered such a dangerous snake. A large snake has long fangs and can deliver a big dose of venom. As with any rattlesnake, give it plenty of space, and if someone is bitten, call 911 and seek emergency medical help immediately.