Pull one thread, the whole net wobbles.

Every thread begins at the Sun.

Here's a game you can't lose: pick any animal, ask what it ate, then ask what that ate, and keep going. You'll always land in the same place — the Sun. Trace your own breakfast back far enough and you'll find a plant standing in the light. The Sun is the battery that charges every living thing on Earth, even the ones that have never felt sunshine in their lives.

Plants pull off the one trick nothing else can do at scale. Using sunlight, water, and the carbon dioxide in the air, they build their own sugary food — that's photosynthesis, and it's why we call plants producers: they produce food out of almost nothing but light. Algae in the ocean and even some bacteria do it too. Producers are the only members of the whole community who don't have to eat anybody. Everyone else is a consumer — a living thing that gets its energy by eating, because it can't make food for itself.

It's easy to picture producers as just the green things you can see — the grass underfoot, the trees overhead. But the busiest producers on the planet are ones you'd need a microscope to spot. Drifting in the top few metres of every ocean are countless tiny algae called phytoplankton, and together they catch roughly as much sunlight as all the forests and fields on land combined. They are the grass of the sea, the first link under almost every fish, whale, and seabird. So whether you're standing in a meadow or floating over a coral reef, the same rule holds: the green stuff comes first, because the green stuff is where energy walks in the door.

So energy enters the living world through one door — producers catching light — and from there it gets passed along like a snack handed down a row of friends. Each step in that handoff is called a trophic level, which is just a fancy word for "rung on the eating ladder." Producers are the first rung. Whatever eats producers is the second. Whatever eats them is the third, and so on up. Every arrow you'll see on this page points the same way the energy travels: from the eaten to the eater, from the snack to the diner.

Five jobs every living place needs filled.

A food web isn't a list of random creatures — it's a set of jobs. Once you know the jobs, you can walk into any forest, pond, or coral reef and figure out who's doing what. Most creatures fit one of these roles, and the role matters more than the name.

Notice that the labels describe what something eats, not how big or scary it is. A tiny ant and a huge moose are both herbivores. That little fact will trip up a famous myth later on — hold onto it.

Watch a sunbeam become a hawk.

Follow the energy along a single thread, one handoff at a time.

Read it left to right and you're watching one parcel of energy change hands. The grass banks a little of the Sun's light as sugar. The grasshopper eats grass and turns some of that sugar into grasshopper. The frog turns some grasshopper into frog, the snake turns some frog into snake, and the hawk turns some snake into hawk. Same energy, new owner each step. The hawk on the end has never tasted sunlight, yet it is, in a real sense, made of the light the grass caught weeks ago.

Five handoffs — and here's the catch nobody mentions at first: at every single one, most of the energy slips away. That leak is so important it gets its own section. Scroll on.

Why is there always room for so few hawks?

Energy doesn't pass up the chain cleanly — only about a tenth survives each step. The rest is spent on living: moving, breathing, staying warm, and finally lost as heat. Drag the slider to change how much sunlight the grass banks, and watch how little is left by the time you reach the top.

This stair-stepped shape is called an energy pyramid, and its squashed top is the whole point. Because roughly nine-tenths of the energy disappears at each rung, a meadow can feed oceans of grass, lots of grasshoppers, fewer frogs, fewer snakes still, and only a handful of hawks. There simply isn't enough energy left near the top to support many large predators — which is exactly why top predators are rare almost everywhere on Earth, and why a chain hardly ever has more than four or five links. By the sixth rung there's basically nothing left to eat.

Where does the missing nine-tenths actually go? It isn't destroyed — energy never is — it just stops being food. A grasshopper spends most of what it eats simply being a grasshopper: hopping, breathing, growing, escaping frogs, warming itself in the sun. All of that work eventually trickles away as heat into the air, and heat can't be eaten. Only the small fraction the grasshopper locks up in new body parts is still on the menu when the frog comes along. Stack that loss five times over and you can see why the top of any pyramid is paper-thin.

There's a neat human consequence hiding in this rule, and your IB course loves it: eating lower on the chain feeds more people. A field of grain can nourish a whole village directly; feed that same grain to cattle first and you keep only about a tenth of its energy as meat. It's the same tenth-at-a-time leak you just dragged on the slider — which is why a plant-rich diet stretches the planet's sunlight so much further than a meat-heavy one.

One chain is a sentence. A web is the whole story.

A food chain is a beautiful little lie. It's true as far as it goes, but it pretends each creature has exactly one meal and exactly one enemy, and that's never how nature works. The hawk in our chain eats snakes — but it also eats mice and rabbits when it can get them. The grasshopper isn't grass's only customer; rabbits and mice crowd the grass too. The mouse might be lunch for the snake and the hawk.

Draw every one of those meals as an arrow and the single line explodes into a tangle. That tangle is the food web, and it tells a richer truth: most living things have several things they eat and several things that eat them. A creature with many food options — like the omnivore bear, or that opportunistic hawk — is called a generalist, and generalists are tough to knock down, because if one food runs out they switch to another. A specialist that eats only one thing, like a panda living almost entirely on bamboo, is far more fragile: lose its one food and it has nowhere to turn.

The more crossings a web has, the more shocks it can soak up — and that helps explain one of the great patterns in nature. Webs near the equator, in rainforests and coral reefs, are bursting with species and absolutely dense with arrows; webs in harsh places like the high Arctic have few species and only a handful of threads. A richly woven web has spare routes for energy to travel, so the loss of any one creature is more easily absorbed. A sparse one, with each species doing a job no one else can cover, is balanced on a knife's edge — which is part of why the simplest ecosystems are often the easiest ones for us to accidentally break.

The difference between a chain and a web isn't just neatness — it's resilience, the ability to take a hit and keep standing. A single chain is brittle: snap any link and everything above it starves. A web has spare threads, detours, back-up plans woven right in. So a healthy web can usually shrug off a small loss... up to a point. The next demo lets you find that point yourself.

Now pull a thread and feel the net wobble.

Here's a real meadow web — eight species, the chains all crossed. Click any creature to remove it, then watch the ripple spread through the net: who runs out of food and fades, and who suddenly booms with one less mouth chasing them. Click it again — or press Restore the web — to put everyone back.

Try the easy ones first: pull out the grass and watch the whole net collapse, because every thread traced back to it. Then try something sneakier — remove the snake, and notice that the frogs and mice it used to hunt suddenly boom, while the hawk, which counted on snakes for dinner, starts to struggle. One removal, ripples running in two directions at once. That double ripple is the heart of the whole topic.

The recyclers turn a ladder into a circle.

So far energy has only travelled one way — up. But matter, the actual stuff bodies are built from, can't just keep climbing and disappearing, or the world would run out of building blocks. This is where the most underrated members of the web finally get the credit they deserve: the decomposers.

When a leaf falls, a grasshopper dies, or a hawk reaches the end of its life, the decomposers move in — fungi (think mushrooms and mould), bacteria, and small recyclers like earthworms and beetles. They break dead bodies and waste back down into simple nutrients and feed them into the soil. Producers drink those nutrients up to grow fresh leaves, and the whole web starts over. So decomposers are the quiet bridge that connects the end of every chain back to the beginning. They take what looks like the top of the ladder and bend it round into a circle.

This is why ecologists like to say nutrients are recycled while energy flows. The carbon and nitrogen in your body have been borrowed and returned countless times — once part of a dinosaur, maybe, then soil, then a fern, then a bug, then you. Energy, on the other hand, is a one-time gift from the Sun: it streams in, gets passed up, leaks away as heat at every step, and is gone. That's the deep reason the Sun has to keep shining. Without it, the recycling could keep spinning for a while, but the energy to drive it would simply run out.

Every living place runs on this one pattern.

The wonderful thing about everything you've just learned is that it isn't really about meadows. It's a pattern, and the pattern repeats everywhere life does — you only swap the actors. Once you can read one web, you can read them all.

In the ocean, phytoplankton are the producers, tiny krill and small fish are the herbivores, bigger fish are the carnivores, and a shark or an orca sits near the top — with crabs and bacteria on the seafloor playing decomposer, raining nutrients back up. In a pond, it's pond weed, then water fleas, then minnows, then a heron. In a desert, it's cactus and tough grasses, then beetles and rodents, then snakes, then an eagle. There's even a thriving web inside the soil beneath your feet, and another in your own gut, where bacteria feed on what you eat. Different costumes, identical script: producers catch energy, consumers pass it up, decomposers send the matter back to the start, and roughly nine-tenths leaks away at every rung.

This is why the food web is such a powerful idea in biology, not just a fun diagram. It's a lens. Hand a scientist a brand-new ecosystem — a cave, a hot spring, a patch of melting Arctic — and the very first questions they ask are the ones you can now answer: who's the producer here, who eats whom, and which threads is everything secretly leaning on?

Humans are in the web too — usually pulling threads.

It's tempting to think of food webs as something happening "out there" in wild places, with people watching from outside. But you eat, so you're a consumer, which puts you squarely inside the web — and humans pull threads harder than almost anything else alive. The trouble is that we often pull without meaning to, and the knock-on effects show up far away from where we tugged.

Overfishing takes so many of one fish that the predators above them starve and the prey below them swarm. Hunting a top predator to make a pasture "safer" can backfire when the deer it used to control overrun and strip the forest bare. Habitat loss — clearing a wood for a road or a field — doesn't remove one species, it cuts a hundred threads at once. And introducing a new creature where it doesn't belong, like cats arriving on an island full of ground-nesting birds, drops a brand-new predator into a web that has no defence against it. Each of these is the remove-a-species demo playing out for real, just at the scale of a whole coastline or continent.

The encouraging flip side is that the same connectedness that spreads damage can spread repair. Bring a keystone predator back and the cascade can run in reverse — when wolves were returned to one large national park, the deer spread out, the nibbled-down trees grew back, songbirds and beavers returned, and the rivers themselves steadied. Understanding the web doesn't just explain how things break. It's the instruction manual for putting them back together.

"The biggest, strongest animal rules the top."

This is the single most common mix-up about food chains, and it's an easy trap, because words like "top predator" sound like a championship belt. They aren't. The food chain isn't a leaderboard of who's strongest — it's a map of who eats whom, and that map ignores muscles entirely.

The clearest proof is in the ocean. The blue whale is the largest animal that has ever lived — bigger than any dinosaur — yet it dines almost entirely on krill, tiny shrimp-like creatures barely longer than your thumbnail. By the logic of who eats whom, that giant sits on a low rung, just one step above the producers, right alongside the grasshopper. Meanwhile a small, unremarkable predator can sit near the top simply because nothing bothers to hunt it.

So drop the idea of strength entirely and remember two cleaner rules. First, the arrows track energy, not power — a chain is a story about where lunch came from, not who would win a fight. Second, being a "top predator" is no safe throne: it's the rung with the least energy left and the fewest backup meals, which is exactly why those animals are rare and why they're so often the first to vanish when a web is disturbed. The top of the chain isn't the winner's podium. It's the thinnest, most exposed branch on the whole tree.