This carefully researched published scientific article (ENERGETICS OF FREE-RANGING MAMMALS, REPTILES, AND BIRDS)¹ presents a well researched method for estimating the field metabolic rate (FMR) of a reptile. We can use this method to estimate how much food a bearded dragon needs to remain healthy and develop properly. 

Before we continue, what is field metabolic rate (FMR)? FMR refers to a metric for the total energy expenditure of an animal in its natural habitat.^{2 3} This includes energy for basic ‘maintenance’ (commonly referred to as BMR in endotherms, this is the amount of energy an organism will need to survive at rest), as well as activities such as movement, digestion, and growth in development. 

In short, FMR describes how much energy (food) an animal needs to be healthy in its natural state. 

Using the model presented by Nagy and Brown, we can estimate a baby bearded dragon’s FMR to be 1.02 calories a day. 

Formula for estimating a lizards FMR in kJ: (.190 * (animal weight in grams)^.916)

Then we divide by 4.184 to convert the units to calories

So, the work for our bearded dragon baby (estimated at 30 grams)⁴, is as follows:

(.190 * (30)^.916)/4.184 = 1.02

Now here’s an important point. Research suggests that FMR estimates for neonate/juveniles, are in fact proportional to FMR rates in adults when body mass is accounted for.⁵ This means our above estimation is scientifically sound and can be used for our general applications. 

With an established estimate of needed energy, we can now move on to converting this into actual food options. 

Let’s start by estimating the calories per insect option: 

Extra Small Roach:

Weight = .04 grams

Protein = 21%

Fat = 9% 

Protein has 4 calories a gram. Fat has 9 calories a gram.

So per gram of dubia roach we have (.21*4)+(.09*9) = 1.65 calories/gram 

Per individual roach, that is .066 calories

Black Soldier Fly Larvae

Weight = Around .05 grams each

Protein = 17%

Fat = 11%

Which equates to about 1.67 calories a gram or about .0835 calories per individual 

Superworms

Weight = Around .15 grams each

Protien = 19%

Fat = 16%

Which equates to about 2.2 calories a gram or about .33 calories per individual 

Hornworms

Weight = Around 1 gram each

Protein = 10%

Fat = 10%

Which equates to about 1.3 calories a gram or about 1.3 calories per individual 

From here, our conversion to rounded full numbers of each insect type is simple. 1 calories is:

• Around 15 small dubia roaches
• Around 12 medium sized BSFL 
• Around 1 small sized hornworm

For the sake of clarity, the nutritional values were provided here, and the estimated weight per insect was provided by our own lab.