When considering which animal eats the most, the answer depends on whether one is referring to the sheer volume of food or the amount consumed relative to its own body size. This relative consumption is a biological phenomenon, often linked to an animal’s metabolic rate and energy expenditure per unit of mass. Examining these “champions of consumption” provides insight into the physiological demands some creatures face to survive and thrive.
The Champions of Consumption
Among the animals that consume the most relative to their size, shrews stand out significantly. The Etruscan shrew, one of the smallest mammals by mass, weighing only about 1.8 grams, must eat between 1.5 to 2 times its own body weight daily to sustain life. Their constant need for food means they hunt almost continuously, often taking down insects and worms larger than themselves.
Hummingbirds are another prime example of high relative consumption. These tiny birds, with the fastest metabolic rate, can eat 1.5 to 3 times their body weight in food per day. Their diet consists of nectar, a sugar-rich liquid, complemented by small insects for protein and minerals. They must feed frequently, sometimes every 10 minutes, to maintain their incredibly high energy levels. The Polyphemus moth caterpillar also consumes up to 86,000 times its own weight during its 56-day larval stage.
The Science Behind High Metabolism
The intense eating habits of small animals like shrews and hummingbirds are directly linked to their exceptionally high metabolic rates. Metabolism converts food into energy, and smaller endothermic (warm-blooded) animals have faster metabolic rates per unit of body mass than larger ones. This inverse relationship stems from the surface area-to-volume ratio. A smaller body has a proportionally larger surface area relative to its volume, losing heat more rapidly.
To counteract heat loss and maintain a stable internal body temperature, these tiny creatures must generate more heat, requiring a constant, rapid energy supply from food. For instance, the Etruscan shrew risks hypothermia due to its high surface area-to-volume ratio, making its extremely rapid metabolism necessary for survival. This high energy demand also fuels their active lifestyles; shrews are constantly active, foraging almost non-stop. The need for heat and energy for basic bodily functions drives their voracious appetites.
Measuring Metabolic Rate
Scientists quantify animal energy consumption using various methods, often focusing on metabolic rate. Basal metabolic rate (BMR) is a common measure, representing the minimum amount of energy to sustain basic functions in a resting, unfed, thermoneutral state. Standard metabolic rate (SMR) is a similar concept, typically used for ectotherms. These rates are important for understanding energy expenditure relative to size.
A primary method for measuring metabolic rate involves quantifying oxygen or carbon dioxide production, as these gases are directly involved in cellular respiration, which generates energy. Specialized chambers monitor these gas exchanges in animals. Allometric scaling is another important concept in this field, describing how biological characteristics, including metabolic rate, change with body size. It reveals that while total metabolic rate increases with body size, mass-specific metabolic rate (energy per unit of body mass) decreases as an animal gets larger. This scaling principle helps explain why smaller animals require disproportionately more food.