How Can an Ant Lift Loads Dozens of Times Its Own Weight?
― The Square-Cube Law That Favours Small Bodies
If you watch a line of ants in a park, you may spot one holding a breadcrumb or a dead insect, far bigger than itself, up over its head as it carries it along. It is often said that if a human had the same strength for their size, they could lift a small car over their head. Why are ants so strong?
Under a park bench, an ant lifts a piece of food several times its own size and carries it above its head. It doesn't stagger or collapse. It just walks steadily back to the nest.
An adult human can hardly ever lift a load dozens of times their own weight. Both are creatures that move by using muscles to hold up and drive the body, so where does the difference come from?
Only one reason it looks so strong: different growth rates
The force a muscle can produce is thought to be roughly proportional to the number of muscle fibres, that is, to the area of its cross-section. When a body gets bigger, area grows only as the "square of length".
Body weight is roughly proportional to the volume of the whole body. Volume grows as the "cube of length", so the bigger a body gets, the faster its weight rises compared with its strength.
"Area goes with the square, volume goes with the cube." This difference in growth is exactly why smaller creatures look stronger for their weight. Let's take it step by step.
The reason: as a body grows, weight outpaces strength
Imagine doubling the size of a body while keeping its shape. Length, width and height all double. The cross-section of a muscle becomes 2 × 2 = 4 times larger, but the volume of the whole body becomes 2 × 2 × 2 = 8 times larger.
Strength, roughly proportional to area, grows only 4 times, while weight, roughly proportional to volume, grows 8 times. So the bigger the body, the worse its strength compared with its weight becomes. Put the other way round, the smaller the body, the better that ratio gets. This is called the square-cube law.
The square-cube law is sometimes used to explain why a flea can jump hundreds of times its own body length, and why an elephant has such thick legs for its size. The bigger an animal is, the thicker and sturdier its bones and legs must be, just to hold up its own weight.
What you can check at home
- Build a paper cube with 2 cm sides and another with 4 cm sides (you can get a feel for it just by drawing the nets, cutting them out and folding them)
- Work out the area of one face and the volume of each (area is "side × side", volume is "side × side × side")
Doing the sums shows that when the side doubles, the area becomes 4 times and the volume 8 times. When size changes, area and volume grow in completely different ways, and that is the secret behind the strength contest between ants and humans.
Summary
An ant seems able to lift dozens of times its own weight not because it has some special power. The smaller the body, the more strength (proportional to cross-sectional area) outweighs body weight (proportional to volume). This is simply a property of body size itself.
Ants weren't born strong.
Being born small is what makes them look strong.
For another case where countless tiny forces add up to something big, see also the article on geckos clinging to glass.
For an example where shape, not size, decides strength, see also why an eggshell won't break when you squeeze it.
For those who want more ― terms, formulas and links to textbooksFrom middle-school science to active research, each part is marked with its level
- Middle schoolCovered in middle-school science and maths
- High schoolCovered in high-school "Basic Physics" and "Basic Biology"
- High school+High-school "Biology", or advanced or sidebar material in textbooks
- UniversityUniversity-level specialist content (biomechanics) not taught in high school
- ResearchTopics researchers are still investigating, not taught even at university as settled fact
Middle schoolTerms: words about body size
- Cross-sectional area: the area of the cut surface when you slice an object. Here it means the cut surface of a muscle.
- Volume: the amount of space an object takes up. It is the basis of body weight.
- Square-cube law: a law that comes from geometry. When length becomes n times larger, area becomes n² times and volume becomes n³ times.
Middle schoolHigh schoolChecking with a formula: how big is the gap between ant and human?
Hearing that "smaller is better" doesn't tell you how big the gap is. The calculation gives a clear number.
Gap in strength-to-weight ratio = body length of the larger ÷ body length of the smaller
| Gap in strength-to-weight ratio | The factor by which one body is "relatively stronger" |
| Body length | Approximate body length of a human and an ant [m] |
This is a simple approximation that follows from strength growing with the square of length and weight with the cube. The ratio of body lengths is directly the ratio of strength-to-weight. Check it by doubling the length: area becomes 2 × 2 = 4 times, volume becomes 2 × 2 × 2 = 8 times, and 8 ÷ 4 = 2 times is the gap that opens up.
| Approximate human height | Take it as 1.5 [m] |
| Approximate ant body length | Take it as 0.005 [m] (5 mm) |
| Ratio of body lengths (human ÷ ant) | 1.5 ÷ 0.005 = 300 [times] |
By this simple calculation, the estimate is that an ant has roughly a 300 times advantage over a human in strength relative to weight.
Suppose a 70 kg human can only just lift about their own weight (roughly 1 times). If they had the same relative strength as an ant, the simple calculation gives 70 × 300 = 21000 kg (21 tonnes), about the weight of several trucks. Of course this is only a theoretical estimate, and real animals involve more complicated factors, but it gives a rough idea of how much being small helps.
High school+UniversityWhat the simple law can't fully explain
Real ants are said to be even stronger than the simple square-cube law can explain. One suggested reason is that ant muscle itself may be built more efficiently, producing more force per unit area than the muscles of larger animals. Another possibility is that a lever system using the exoskeleton (the hard shell covering the outside of the body) as its pivot passes force to the joints efficiently.
In other words, real strength is thought to be the combined result of "the effect of body size" and "differences in the efficiency of muscle and skeleton itself", and some parts remain that a simple scaling calculation cannot explain. The same square-cube law also plays a part in how body size affects a cat falling from a height.
ResearchWhat is still not well understood
- Predicting in theory, from body size alone, how much force an ant's leg or neck joints can actually withstand is still not possible with any confidence. Some observations show ants stronger even than the simple square-cube law predicts, and researchers are still working out factors the law can't explain, such as muscle efficiency and joint structure.
- Why the muscles of very small creatures can produce so much force per unit area, at the microscopic level, is said not to be fully understood.
- The square-cube law is also applied in robotics. Research on how to design insect-sized robots so they produce force efficiently is said to be still developing.
Even the ants in a nearby park still have the details of their strength under study. Being familiar and being understood are two different things.
Links to textbooks (by level)
| Level | Subject / unit | Where in this article |
|---|---|---|
| Middle school | Maths: area and volume ratios of similar figures | Comparing 1×, 2× and 3× cubes |
| High school | Basic Biology: structure and function of the body | Strength and area, weight and volume |
| High school+ | Biology: animal behaviour and body mechanisms (advanced) | Calculation comparing ant body length |
| University | Biomechanics, comparative anatomy | Exoskeleton lever system, muscle efficiency |
| Research | Insect biomechanics, robotics (unresolved) | Predicting joint strength, muscle mechanisms at tiny scales, use in small robots |
| ― | Everyday observation | Checking area and volume ratios with paper cubes |
- Galilei, G., Discorsi e dimostrazioni matematiche (1638, a classic account of the square-cube law).
- Alexander, R. McNeill, Principles of Animal Locomotion (a foundational text on body size and locomotor ability).
- Explanatory materials on insect biomechanics and exoskeleton structure.
- General descriptions of area and volume ratios of similar figures in biology and maths textbooks.
※ Figures such as body length and the multiple of weight that can be lifted vary with species, individual and measurement conditions. This article gives commonly used rough values.
※This article is a general-audience science explanation. Figures for body length and weight ratios vary with species, individual and measurement conditions, and are given as rough guides to understanding the mechanism.