Lizards: building a salad for a plant-eating lizard

Quick answer

Reading the label on a tub of pellets tells you almost nothing about whether a plant-eating lizard is being fed properly, because the salad is where the diet is won or lost. For adult bearded dragons, uromastyx and green iguanas, the daily bowl of greens is the diet, and the commonest serious diseases in these animals come from getting it wrong.

Two mistakes dominate. Feeding too much animal protein to a herbivore, which loads the body with uric acid and produces gout and kidney damage. And building the salad from foods with more phosphorus than calcium, or from foods that bind calcium, which produces metabolic bone disease even when a calcium supplement is being used.

The salad matters more than any packet. For an adult plant-eating lizard it is the whole diet, not a side dish.

• A juvenile bearded dragon and an adult one need close to opposite diets.
• Adult uromastyx and green iguanas should not be eating insects, dog food, cat food or any animal protein.
• Reptiles excrete nitrogen as uric acid, which is barely soluble. Excess protein plus dehydration equals gout.
• Spinach, chard and beet greens bind calcium and should never be the base of a salad.
• A cool lizard cannot digest a good salad. Temperature is part of the diet.

Decide in 60 seconds

Why protein is the dangerous nutrient

Mammals convert excess nitrogen into urea and excrete it dissolved in urine. Reptiles convert it into uric acid, which they excrete as a semi-solid white or off-white urate. That adaptation saves an enormous amount of water and is why desert reptiles can live where they do.

The cost is that uric acid barely dissolves. If more is produced than can be excreted, or if the animal is dehydrated so that what is being excreted is more concentrated, uric acid comes out of solution and forms crystals.

Those crystals are deposited in two places. In joints, producing articular gout: swollen, painful joints, reluctance to move, and a lizard that sits still and refuses to climb. And around the internal organs, producing visceral gout, which is usually silent until the animal is very unwell.

Excess dietary protein drives the production side. Dehydration drives the concentration side. A herbivorous lizard fed dog food in a dry enclosure with no drinking water is being pushed from both directions at once.

Once urate crystals are deposited they are extremely difficult to remove and the kidney damage that accompanies the process does not reverse. This is a disease to prevent rather than to treat.

Calcium, phosphorus and why the supplement is not enough

Bone requires calcium and phosphorus in proportion. Widely used reptile guidance puts the target at roughly twice as much calcium as phosphorus across the whole diet.

Most vegetables and almost all fruit have the reverse ratio, with more phosphorus than calcium. A salad built from fruit, courgette, tomato and pepper is inverted, and an inverted ratio pulls calcium out of the skeleton no matter how much calcium powder is dusted on top.

Oxalate is the second trap. Spinach, chard, beet greens and rhubarb are high in oxalate, which binds calcium in the gut into an insoluble compound that the animal cannot absorb. A salad of spinach dusted with calcium powder delivers less usable calcium than a salad of collard greens with none.

The third component is vitamin D3, without which dietary calcium is not absorbed. In most captive lizards that comes from appropriate UVB lighting rather than from food, which is why a nutrition article has to talk about the lamp. A perfect salad in an enclosure with an expired UVB bulb still produces metabolic bone disease.

So there are four things that have to be right together: the calcium content of the food, the phosphorus content of the food, the absence of large amounts of oxalate, and functional UVB. Getting three of them right is not enough.

Chop to a size the animal can swallow easily, offer in a shallow wide dish, and put it in after basking has started rather than first thing.

Building the salad

Base it on calcium-rich, low-oxalate leaves.

Collard and spring greens, turnip greens, mustard greens, dandelion greens, endive and escarole, and prickly pear pads where you can get them. These are the foods that carry a favourable calcium to phosphorus ratio without a large oxalate load, and one or more of them should make up the bulk of the bowl.

Rotate the brassicas rather than relying on one.

Kale, cabbage, broccoli, bok choy and mustard greens are all useful, and all contain compounds that interfere with iodine uptake if one of them becomes the sole daily staple. Rotation solves this. Exclusion is unnecessary.

Add vegetables for variety and fibre.

Butternut and other squashes, green beans, snap peas, bell pepper, okra, parsnip in moderation. These broaden the nutrient profile and add texture.

Keep fruit small and occasional.

Fruit is high in sugar, has an inverted calcium to phosphorus ratio, and in bearded dragons contributes to loose stool. Use it to make a new salad interesting, not as a component of the daily bowl.

Do not build a salad on lettuce.

Iceberg is close to nutritionally empty. Romaine is better but is still mostly water and should not be the base.

Never feed avocado, rhubarb, or the onion family.

Feed uromastyx as the desert herbivores they are.

High-fibre plant material, dried pulses and seeds as many keepers use, and no fruit. Adults do not need routine insects, and feeding them regularly pushes exactly the protein problem described above.

Feed iguanas no animal protein at all.

At any age. The historical practice of feeding iguanas dog food or monkey biscuit is responsible for an enormous amount of kidney disease.

Presentation and timing

Chop everything small enough that the lizard can swallow it without extended chewing, and mix it rather than layering, or the animal will pick out the favourites.

Use a shallow wide dish rather than a deep bowl.

Offer it after the animal has warmed up and started basking, not before. A cold lizard will not eat and will not digest.

Take it out before it wilts or dries, particularly in a hot enclosure, and never leave old salad in overnight where it will grow mould and attract insects.

Dust with a calcium supplement as advised. The schedule depends on the species, the age of the animal, the UVB provision and the specific product, so take it from a reptile vet or from the manufacturer's guidance for that species rather than from a general rule.

Mist the greens lightly. Herbivorous lizards obtain a large part of their water from food, and moist greens contribute meaningfully to hydration in a species that may not drink from a bowl.

Temperature is part of the diet

Herbivorous lizards do not digest plant fibre themselves. They house microbial populations in an enlarged hindgut, and those microbes ferment the fibre and release nutrients the animal can absorb.

That fermentation is temperature dependent. Below the correct range it slows down and eventually stops, and undigested plant material sits in the gut.

The practical consequences are direct. A lizard kept too cool will eat less, digest less of what it eats, produce abnormal droppings, and lose weight on a diet that looks correct on paper. A lizard with no proper basking spot cannot raise its body temperature enough to start the process at all.

So the first thing to check when a plant-eating lizard is doing badly on a good salad is not the salad. It is the hot end temperature, measured with an instrument at the surface where the animal actually sits, the gradient across the enclosure, and the night-time temperature.

Variety visible in the bowl is the goal. A salad that looks the same every day is usually built on one or two items and is carrying whatever imbalance those items have.

Getting a reluctant lizard onto greens

Adult bearded dragons that were raised on insects frequently refuse salad, and owners give in because the animal is clearly hungry and clearly wants crickets.

Offer salad first, insects later. Put the salad in as soon as basking starts and offer insects only after it has been available for a period.

Make it move. Some lizards respond to movement. Placing a live insect on top of the salad, or gently agitating the bowl, triggers a feeding response that then includes what is underneath.

Use scent transfer. Mixing a small amount of a strongly flavoured accepted item into the greens, then reducing it over weeks, works for many animals.

Reduce the insect portion gradually rather than removing it. Abrupt withdrawal produces a standoff, and an adult lizard can hold out longer than most owners can.

Check the temperature first. A lizard that is not eating salad may not be refusing it, it may be too cool to feel like eating at all.

Be patient. Diet transitions in adult reptiles take weeks to months. That is normal and is not a sign it is not working.

What to monitor

Weight, on a gram scale, at the same interval. Trends matter more than single readings.

Body condition, which in bearded dragons is read partly from the fat pads at the base of the tail and behind the head, and in most species from whether the hip bones and spine are prominent.

Droppings and urates. Urates should be white or off-white and soft. Chalky, hard, yellow or orange urates suggest dehydration and are worth acting on before anything else happens.

Movement and grip. A lizard that has stopped climbing, is reluctant to walk, or holds a limb differently should be seen, because both gout and metabolic bone disease present that way.

The jaw and limbs. Softening of the lower jaw, swellings along the limbs, tremors or a rubbery feel to the bones are metabolic bone disease and need urgent attention.

Basking surface temperature, hot and cool end air temperatures, and the UVB bulb's installation date.

Where the usual advice goes wrong

"Feed a commercial herbivore pellet as the main diet."

Pellets can be a component and they are not a substitute for fresh plant material, which supplies the fibre, the moisture and the variety these animals need.

"Spinach is a superfood, it must be good for them."

Spinach is high in oxalate, which locks up calcium. It is one of the worst possible bases for a reptile salad.

"Add extra calcium powder and the ratio sorts itself out."

Powder cannot correct an oxalate problem, cannot fix an absent UVB bulb, and does not compensate for a diet built from phosphorus-heavy foods. Fix the food first.

"Adult bearded dragons still love crickets, so they should have them."

They do, and an adult fed like a juvenile becomes overweight, develops fat in the liver, and increases its protein load. Adults are plant-led.

"A little dog food gives an iguana some protein."

This single piece of outdated advice has probably killed more captive iguanas than any other. No animal protein.

"Fruit is natural, so it is fine."

Most fruit has an inverted calcium to phosphorus ratio and a high sugar content. Occasional is fine. Daily is not.

"He will not eat salad, so I feed what he will eat."

An adult herbivore that eats only insects is being harmed by that arrangement. The transition takes weeks and is worth doing properly.

What never to do

Do not feed animal protein to an adult herbivorous lizard.

Do not build a salad on spinach, chard, beet greens or iceberg lettuce.

Do not feed avocado, rhubarb or anything from the onion family.

Do not rely on a calcium supplement to correct an inverted diet.

Do not assume the UVB bulb is working because it is emitting visible light. Output falls long before the lamp fails.

Do not offer food to a cold lizard, and do not leave uneaten salad in a hot enclosure.

Do not make a rapid diet change in an adult reptile. Weeks, not days.

Do not give a supplement, wormer or medication intended for another species.

When to get help

See a reptile vet promptly for swollen joints, reluctance to move or climb, a limb held differently, softening of the lower jaw, tremors, or a rubbery feel to the bones.

See a vet for chalky, hard, yellow or orange urates, for weight loss on an apparently adequate diet, for a lizard that has stopped passing droppings, and for any animal that has been fed animal protein as a herbivore for a prolonged period.

Book a routine check to review the diet and the UVB setup when you take on an adult lizard whose history you do not know, and before making a major diet change in an animal that has been fed one way for years.

A lizard that basks, eats its salad, passes normal droppings with soft white urates and holds a steady weight is telling you the diet and the heat are both right.

Bring the exact species, the animal's age and how long you have had it, a photograph of a typical salad bowl, a list of everything fed in a normal week including insects and treats, the supplement products and how often each is used, measured basking surface and cool end temperatures, the UVB bulb type and its installation date, the weight record, and a photograph of a recent dropping including the urate. Expect the vet to assess hydration and to consider blood testing and imaging if gout or kidney disease is suspected.