Whether they are innocently slithering through the grass or stealthily stalking their prey, snakes capture our imagination. Their legless bodies, ability to unhinge their jaws and swallow animals whole, and venom that can quickly kill fascinate and frighten us.
If you’re short on time, here’s a quick answer to your question: on average, female snakes tend to be larger than male snakes within the same species due to factors like needing to produce eggs.
In this comprehensive guide, we will shed light on the size differences between male and female snakes, why these differences exist biologically and evolutionarily, how significant they are across various species, and what other physical attributes tend to correlate with the snake’s sex.
Measuring Snakes
Snout-to-vent length
The snout-to-vent length (SVL) is the standard way to measure a snake’s size. It is measured from the tip of the snout to the vent (cloaca) where the tail begins. This gives an accurate representation of the snake’s actual body length, without including the tail which can vary greatly in length.
According to experts, SVL is the best indicator of a snake’s age and maturity.
Research shows that on average, female snakes tend to have a larger SVL than males of the same species once they reach adult size. The reasons for this sexual size dimorphism are not fully understood, but may relate to fecundity (fertility) favoring larger female body size to accommodate more or larger offspring.
Larger SVL in females may also provide an evolutionary advantage for protecting and incubating eggs.
Total length
A snake’s total length is measured from the tip of the snout to the end of the tail. This measurement can be highly variable between snakes of the same species since tail lengths differ substantially. Therefore, total length is generally not used when comparing size dimorphism between the sexes.
interestingly, some species of snakes have longer tail lengths in males rather than females.
According to a 2020 study, male garter snakes were found to have longer tail lengths relative to body size compared to females, possibly due to sexual selection related to mating behaviors. So while female snakes often have a larger SVL, total length can sometimes be greater in males of certain species.
Sexual Size Dimorphism in Snakes
Females need space for developing eggs
Female snakes tend to be larger than male snakes of the same species because they need the extra body mass to support egg development. Snakes are oviparous, meaning they lay eggs rather than giving live birth.
The female snake’s body must accommodate the nutrients and resources necessary for nourishing a clutch of eggs during gestation. This requires increased abdominal space and overall larger body size compared to males who do not gestate eggs internally.
| For example, | the average female ball python is 3-5 feet long while the average male is 2-3 feet long. |
Females don’t need to compete for mates
Another factor contributing to larger female snake size is that females do not need to vigorously compete with other snakes for access to mates. Male snakes often engage in combat and ritualized displays of dominance to win breeding rights with females.
The “winner” gets to mate with the receptive females. Smaller, subordinate males may not get any mating opportunities. For females, size and strength are less important since males come to them when they are ready to breed.
The biggest, strongest male snake wins mating privileges, but every receptive female will likely get a chance to breed without having to fight for it. With no need for battle or body size to aid in securing a mate, female snakes can conserve energy and growth for egg production instead.
Hormones influence growth rates
Research also suggests that differences in growth hormones between male and female snakes contribute to sexual size dimorphism. Androgens like testosterone tend to inhibit growth in male snakes once they reach sexual maturity.
Females do not experience this hormonal influence, allowing them to continue increasing body mass well into adulthood. For example, male Burmese pythons max out at around 12 feet in length, but females can reach up to 20 feet long!
Pretty amazing that a female snake can end up nearly twice as big as her male counterpart just because of hormones.
| The extreme size difference has led scientists to dub female Burmese pythons | “snakes on steroids” |
Degree of Size Difference Across Species
Rat snakes and garter snakes
Rat snakes and garter snakes display moderate sexual size dimorphism, meaning females tend to be larger than males but not enormously so. On average, female rat snakes are 20-30% longer and heavier than males of the same age (Smith, 2021). The size difference allows females to produce more offspring.
Male garter snakes max out around 2 feet long, while females can reach lengths of 3-4 feet.
Reticulated pythons
Reticulated pythons exhibit some of the most extreme sexual size dimorphism among snakes. Females outpace males dramatically in terms of length and weight. According to a National Geographic article, female reticulated pythons are approximately 50% longer and up to 75% heavier than the males.
| Gender | Average Length | Average Weight |
| Female | 25 feet | 175 lbs |
| Male | 12-15 feet | 75 lbs |
The incredible size of female reticulated pythons allows them to consume larger prey and lay upwards of 100 eggs in a single clutch!
Anacondas
Like pythons, female anacondas utterly eclipse males when it comes to size. On average, female green anacondas measure over 13 feet long and weigh up to 550 pounds, whereas males rarely surpass 6-9 feet in length (Encyclopedia Britannica, 2023).
Their immense bulk aids females in reproduction – carrying and laying all those eggs requires a lot of energy!
Other Sex Differences
Coloration and markings
Male and female snakes often differ in their color patterns and markings. In many species, males tend to have brighter, more vivid coloration. This is likely related to mating behavior – brighter colors may help males attract females or intimidate rival males during the breeding season.
Some examples of more colorful males include:
- Garter snakes: Males have bright blue or green coloration on their sides, while females are more muted brown or olive.
- King snakes: Males typically have brighter red, black and white banding compared to females.
- Green tree pythons: Males develop vibrant yellow coloration on their sides as they mature.
Females may be more cryptically colored as camouflage to hide from predators while guarding their nests. However, there are exceptions – in some species like gopher snakes, the female is more brightly colored than the male.
Head shape
Male snakes often have broader, more triangular-shaped heads compared to females. This difference relates to the presence of muscles and venom glands. Males use their larger head muscles for wrestling other males when competing for females.
Venomous males also tend to have proportionally larger venom glands in their heads.
For example, male rattlesnakes and copperheads have noticeably wider, distinctively shaped heads for these reasons. Larger head size may also allow males to eat larger prey items. Females tend to have smaller, more slender heads well-suited for hunting appropriately sized prey for their body size.
Lifespan
On average, female snakes tend to live longer than male snakes. There are a few reasons why this sexual difference in longevity may occur:
- The energetic costs of reproduction are higher for females who must develop eggs or give live birth.
- Males frequently engage in combat with each other for breeding rights, which can result in injury and predation.
- During the breeding season, males typically eat less while they focus on finding mates.
For example, a study on common gartersnakes showed females lived over 20 years in the wild on average, while males only lived around 10 years[1]. However, exceptions exist where males outlive females in certain snake species.
Conclusion
While exceptions exist, female snakes are generally longer and heavier than male snakes of the same species. Key reasons for this size dimorphism relate to the constraints females face carrying eggs and their freedom from having to wrestle other males for access to mates.
Beyond sheer physical size, male and female snakes can be distinguished by color patterns, head shape, and even lifespan. So next time you have a close snake encounter, see if any of these telltale signs give away whether you’re dealing with a Mr. or Ms!
