Lizard diarrhoea: reading the dropping and the order to work through

Quick answer

Most of the answer comes from the dropping and the enclosure, not from handling the lizard. Support the whole body when you do lift one.

Before anything else, confirm that what you are seeing is actually diarrhoea. Lizards pass faeces, urates and urine through a single opening, so a normal dropping is a firm dark portion, a white or cream urate portion, and often a clear watery portion alongside them. Owners routinely report the clear liquid as diarrhoea when the faecal part is perfectly formed.

If the faecal portion itself is unformed, watery, mucoid, frothy or bloody, that is diarrhoea, and the first thing to check is not the lizard. It is the temperature.

• Verify basking surface and cool end temperatures with a probe or infrared thermometer before you change anything else. Reptile digestion runs on heat.
• Photograph the dropping in place, with something for scale, before you clean it up.
• Collect a fresh sample in a sealed clean pot. Do not freeze it and do not let it dry out.
• Never give an over-the-counter wormer. It does nothing to the protozoa that cause most reptile diarrhoea, and some wormers kill some reptiles.
• Diarrhoea in a hatchling or juvenile is urgent. Small bodies dehydrate fast and have almost no reserve.

:::danger
Never treat a reptile with ivermectin unless a reptile vet has prescribed it for that animal.

Ivermectin is fatal to chelonians and dangerous in several other reptile groups. It is also freely available as a livestock product, and owners reach for it because it is cheap. Dosing across reptile species is not interchangeable, and the products sold for dogs, cats, birds or sheep are not scaled for a lizard. If a wormer is needed, the drug and the dose are a veterinary decision made after the parasite has been identified.
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Decide in 60 seconds

Why heat comes before parasites

A lizard cannot generate its own body heat. Every enzyme in its gut, and the smooth muscle that moves food along it, works at a rate set by body temperature.

When the enclosure runs below the species' preferred range, transit slows and food sits in the intestine longer than it should. Bacteria ferment what has not been digested, which produces gas, irritation and a loose, foul, undigested-looking stool. In herbivorous lizards, which rely on hindgut fermentation, the effect is more pronounced still, because the entire digestive strategy depends on being warm enough.

This is the single most common cause of loose droppings in a pet lizard, and it produces exactly the same appearance as a parasite problem.

It is also the reason temperatures come first in the sequence. A faecal test that finds a few pinworms in a lizard kept too cool will send you chasing the pinworms, and the diarrhoea will continue.

Cool enclosures happen quietly: a thermostat probe that slipped, a basking bulb losing output before it fails, a room that dropped with the season, a new lamp at a different distance, or a lizard that has grown and can no longer get close enough to the heat source.

Measure at the surface the animal actually sits on, and measure the cool end too. A stick-on strip on the glass reads the glass.

Reading the dropping

A gram scale, a written log and the actual supplement pot answer more questions at the appointment than any description of the droppings will.

Three components, each of which tells you something different.

The faecal portion should be firm, formed, dark brown to near black, and hold its shape. It carries a smell, but not an overpowering one.

The urate portion is the reptile equivalent of urine, excreted as solid uric acid rather than dissolved urea. It should be white to cream and soft to slightly chalky. Yellow or orange urates suggest dehydration or liver involvement. Hard, gritty, crumbly urates suggest dehydration. Green urates in an animal that has not eaten often reflect bile.

The liquid portion is genuine urine. Its volume varies with species, drinking, soaking and diet.

Now the differentials.

That last row matters. Owners see liquid and assume the gut is moving too fast, when a partial obstruction can produce watery output because only fluid gets past. A lizard with loose droppings that are also becoming less frequent and smaller in total volume needs imaging, not a diet change.

What is actually causing it

Husbandry, most often.

Temperature is first. Then humidity, because a chronically dehydrated lizard has slower gut transit and firmer material that irritates as it passes. Then diet: too much fruit in an omnivore, too much high-water salad in a herbivore, feeder insects that were gut-loaded on something unsuitable, an abrupt change of pellet or produce, or simply too much food.

Protozoa.

Coccidia are very common in bearded dragons and cause chronic diarrhoea, poor growth and weight loss, especially in juveniles from mixed-source collections. Flagellates are found in many species and can overgrow when an animal is stressed or kept badly. Entamoeba invadens is carried without illness by some reptiles and is lethal in others, which is one of the strongest arguments against mixing species in one enclosure or sharing equipment between enclosures.

Cryptosporidium deserves separate mention. In leopard geckos it produces the picture owners call stick tail: chronic diarrhoea, regurgitation, and steady loss of the fat stored in the tail despite continued eating. It is highly contagious between reptiles, persists in the environment, and there is no reliable cure, so identifying it changes everything about how the collection is managed.

Worms.

Nematodes, including pinworms, are common. Low numbers of pinworms in a lizard are often incidental and not the cause of anything, which is precisely why treating on suspicion is a poor strategy.

Bacteria.

Usually secondary to poor hygiene, poor temperatures or another primary disease. Salmonella lives in many healthy reptiles without causing them illness, so finding it does not explain the diarrhoea, though it matters for the household.

Everything else.

Foreign body or substrate impaction, antibiotics given for something else, toxin exposure, liver or kidney disease, and in females reproductive activity pressing on the gut.

Stress.

Real, but rarely a sufficient explanation on its own and never a diagnosis of first resort. If a new lizard has loose stools in its first weeks, the likeliest cause is the parasites it arrived with plus an enclosure still being dialled in, not its feelings about the move.

Staging: what this looks like as it progresses

Early. One or two soft droppings. The lizard is alert, basking normally, eating, and weight is steady. This is the stage where a temperature check and a diet review usually solve it.

Established. Every dropping is loose. Smell changes noticeably. Appetite starts to drop, or stays normal while weight falls, which is the more sinister version. Urates turn yellow and start to look dry. The lizard spends longer under the heat source than usual, because a sick reptile seeks warmth.

Late. Eyes look sunken. Skin over the flanks stays tented when gently lifted. The mouth membranes are tacky and saliva becomes stringy. The lizard stops basking, which is the point at which body temperature falls, digestion stops altogether and immune function collapses. Straining may produce a cloacal prolapse.

Owners often describe the late stage as sudden. It is not sudden. It is the first stage nobody was measuring.

What to do at home while you arrange the appointment

Work in this order.

Measure and correct temperatures. Basking surface and cool end, with a probe or infrared thermometer, at the height the animal sits. Correct anything outside the species range before changing anything else.

Check humidity against the species requirement, and check the water provision matches how that species drinks. Bearded dragons and many agamids use a bowl. Chameleons take moving droplets and generally ignore standing water. Crested geckos drink from misted surfaces. A full water bowl proves nothing about whether the animal is drinking.

Revert recent changes. Go back to the previous diet, the previous supplement, the previous substrate. Change one thing at a time afterwards.

Support hydration carefully. A shallow, warm, supervised soak helps some species by encouraging drinking and softening the skin. The water should be shallow enough that the head is never at risk, the animal is never left alone, and a weak or collapsing lizard is not soaked at all without veterinary advice.

Do not fast a juvenile. Adults tolerate a short reduction in food; hatchlings and juveniles do not.

Clean and disinfect the enclosure, remove and replace substrate, and disinfect bowls and decor. Faecal-oral reinfection is the reason many treated animals relapse.

Separate cohabiting animals and use separate tools, bowls and hands for each, in that order.

Collecting a sample the laboratory can actually use

This is where owners lose diagnostic information without realising.

Motile protozoa are identified on a warm fresh direct smear and become unrecognisable as the sample cools and dries. A sample that has spent two days in a fridge can return a clean result on an animal that is riddled.

What changes the answer

Clear, full eyes, taut skin, good muscle over the hips and tail base. This is the baseline you are comparing a sick animal against.

Age. A hatchling or juvenile has a small water reserve, a high surface area relative to volume, and a growth demand that cannot pause. Diarrhoea that an adult would shrug off can kill a juvenile within days.

Species and feeding strategy. Herbivorous lizards such as uromastyx and iguanas depend on a warm hindgut and normally pass firm, dry droppings, so loose output in them is a strong signal. Insectivores like leopard geckos give you the tail as a fat gauge, which is a genuinely useful early indicator. Chameleons live closer to the dehydration line than almost any other commonly kept lizard, so diarrhoea in one is more urgent.

Origin. Wild-caught animals arrive with substantial parasite burdens and a history you cannot reconstruct. Captive-bred animals from large mixed collections still commonly carry coccidia. Home-bred animals from a small closed collection carry less. Ask where the animal came from, and say so at the appointment.

Cohabitation. Any shared enclosure means a shared faecal-oral load and no way to tell whose droppings you are looking at. If output is abnormal in a group, separate them so you can attribute it.

Season. In species that brumate, reduced intake and altered output during cooling are expected. Diarrhoea is not. Cooling for brumation in an animal with an untreated gut infection is dangerous and should not be started without a clean bill of health.

Sex and reproductive state. A gravid female's gut is physically compressed and her output changes. That is different from diarrhoea, and the distinction is worth raising with the vet.

The failure modes of the usual advice

"Give it a wormer."

Broad-spectrum wormers do not treat coccidia, do not treat Cryptosporidium, and do not treat flagellate overgrowth, which between them account for most infectious reptile diarrhoea. Dosing an animal on suspicion also wastes the diagnostic window and can make the animal worse. Some products are directly dangerous in some reptile groups.

"Warm it right up."

Raising temperatures above the species range does not burn out an infection. It dehydrates the animal further and risks thermal injury in an animal too weak to move away.

"Fast it for a week to rest the gut."

Fasting does not address the cause and removes the intake an already-depleted animal needs. In a juvenile it is dangerous.

"Add a probiotic."

Reasonable as a supporting measure after a diagnosis, especially after antibiotics. Not a treatment for a parasite, and not a reason to delay a faecal test.

"Give it electrolyte drink."

Oral rehydration solutions formulated for humans or livestock are not appropriate to pour into a lizard, and a dehydrated reptile that will not drink usually needs fluids given by a vet rather than by mouth.

"It cleared up, so it is fine."

Chronic protozoal infections wax and wane. An animal that improves and relapses over months is the typical presentation, not the exception. If it has come back once, test.

What the vet will ask for

Species, age, sex if known, and where the animal came from. How long you have had it, whether it was quarantined, and whether it lives with anything else.

Measured hot end, cool end and overnight temperatures, and how you measured them. UVB lamp type, age and distance, and whether mesh sits in between. Humidity and how it is maintained. Substrate.

The full diet, including what feeder insects are gut-loaded on, what supplement is used and how often, and any change in the last month.

Weight history, appetite, shedding history, and when the droppings first changed.

Photographs of the droppings, ideally several over several days, and a fresh sample.

Any medication, supplement or treatment already given, including anything bought over the counter. Say it even if you would rather not, because it changes what the results mean.

What never to do

Do not medicate before a diagnosis, and never with a product intended for another species.

Do not raise temperatures beyond the species range, and do not use an unthermostatted heat source on a weak animal.

Do not soak a collapsed or unresponsive lizard. Aspiration and drowning are real risks in an animal that cannot hold its head up.

Do not freeze or dry a faecal sample you intend to have tested.

Do not put a sick lizard back into an uncleaned enclosure after treatment.

Do not assume a healthy appetite means the animal is fine. Eating well while losing weight is one of the more specific pictures in reptile parasitology, not a reassurance.

Do not handle a lizard with diarrhoea and then eat or prepare food without washing hands thoroughly. Household hygiene matters here regardless of what is causing it.

When to get help

The endpoint is a lizard back on its basking site with formed droppings and a stable weight, in an enclosure that has been cleaned out properly.

Same-day reptile veterinary care for fresh blood or black tarry material in the droppings, tissue protruding from the vent, straining, sunken eyes with tented skin, a lizard that has stopped basking, or any of these in a hatchling or juvenile.

This week for loose droppings that persist beyond a few days, any weight loss, mucus or froth, a thinning tail base in a gecko, or diarrhoea in a newly acquired or wild-caught animal.

Bring the sample, the photographs, the food, the supplements and the numbers. In reptile medicine the enclosure is usually a large part of the diagnosis, and a description of it is worth much less than a measurement.