Bloodsuckers — are vampires among us?
Welcome to the vampire apocalypse calculator, you lovely, tasty human. This tool is based on the predator–prey model — a model that successfully describes the dynamics of ecosystems, chemical reactions, and even economics. Now it's time to use it to answer the question: what if vampires were among us?
You might think we're joking, but if you compare the actual world population to a pure exponential growth model, something seems to be preventing the expansion of humanity. We could theorize all day about why this is, but there's one idea we'd like to check: vampires. Are you ready to unveil the ancient mysteries of vampirism? 🦇
What is vampirism?
Nearly every culture around the world has its own blood-drinking creature. The ancient world had the female demons Lilith (Babylonia) and Lamia (Greece). In Africa, the Ewe folklore believes in the Adze — a vampiric being that can take the form of a firefly. The Chilean Peuchen was a gigantic flying snake that could paralyse its prey, and in Asia the Penanggal was a woman cursed to become a bloodsucking demon. So why is it that vampires are known all over the globe? Isn't it suspicious?
Vampires are usually believed to be undead creatures with supernatural powers: they don't age, can fly, and regenerate from almost any wound. They crave human blood but fear sunlight, silver, religious symbols, and garlic. They can be killed by decapitation or a wooden stake through the heart. The last important detail: vampires can't reproduce — they can only turn a human into a new vampire.
How to use the vampire apocalypse calculator?
The vampire apocalypse calculator lets you check how humanity would fare in selected scenarios from popular books and movies, or in a story you build from scratch. The result is a graph plotting how three populations change over time: humans (blue), vampires (red), and vampire slayers (yellow). Adjust the time scale (days, weeks, months, years, decades, centuries) and the chart type (linear or logarithmic) to frame the story best.
The algorithm receives up to 13 parameters from the three species:
- Humans — if left alone, their population grows exponentially. You set the initial population, the probability of turning into a vampire when attacked, and the annual population growth. Their special ability lets them grow faster when the population falls below its starting value.
- Vampires — bloodthirsty humanoids that hunt people and turn them into new vampires. You set their initial population and their aggression toward humans and slayers. Their special ability makes them smarter: they refrain from killing too many humans so they don't lose their only food source.
- Vampire slayers — an organisation of brave people trying to save the world. You set their initial population, annual recruitment speed, aggression toward vampires, and the probability of being turned into a vampire. Their special ability caps the size of the organisation so it doesn't grow forever.
For example, build a custom scenario: a city of one million people growing at a typical 1% per year. Suddenly 200 vampires invade and start attacking people, with a human-to-vampire transformation probability of one half. Increase the time scale to decades and watch what happens — will mankind be wiped out, or can a handful of slayers turn the tide? Try playing with different options!
Predator–prey model: Lotka–Volterra equations
Galileo Galilei once said that mathematics is the language in which God has written the universe. Scientists all around the world try to find equations that describe the natural world properly.
If you consider a simple ecosystem with two species — say, foxes and rabbits — the Lotka–Volterra equations generally work just fine. They are also called the predator–prey model. Rabbits can peacefully live and reproduce with unlimited food, while foxes are carnivorous, so their population depends on the availability of rabbits. More rabbits mean more foxes, but more foxes mean fewer rabbits — and the two populations oscillate.
A similar situation exists with humans (prey) and vampires (predators). This calculator uses the Lotka–Volterra equations with a few modifications. First, we added vampire slayers that control the vampire population. Second, we gave each group a special ability implemented indirectly in the algorithm. In short, the model tracks three coupled populations:
dHumans = growth·Humans − attacks·Vampires·Humans dVampires = turned·attacks·Vampires·Humans + turned·attacks·Vampires·Slayers − kills·Slayers·Vampires dSlayers = recruitment·Slayers − attacks·Vampires·Slayers
The calculator integrates these equations numerically, step by step, so re-loading a shared link reproduces the same outbreak.
American and metric units
Vampires feed on blood, so the calculator also reports how much blood was drained over the whole outbreak. An average adult holds about 5 litres of blood, and we sum up every victim taken by the vampires. Switch between metric (litres) and American (US gallons) to see the grisly total in your preferred units. 🩸
🙋 Want to build your own Minecraft vampire world? Take a look at the Minecraft circle generator or the Nether portal calculator to help you with some of the details!
Based on the work of Wadim Strielkowski, Evgeny Lisin and Emily Welkins, Applied Mathematical Sciences. This is a fun approximation, not a scientific prediction.