Gastrointestinal parasitism in tarantulas (roundworms)
Gastrointestinal parasitism caused by roundworms (nematodes) is a rare but documented condition in large terrestrial tarantulas such as the Goliath birdeater (Theraphosa blondi). These parasites live in the animal's digestive tract and disr...
What is it?
Gastrointestinal parasitism caused by roundworms (nematodes) is a rare but documented condition in large terrestrial tarantulas such as the Goliath birdeater (Theraphosa blondi).
These parasites live in the animal's digestive tract and disrupt digestion.
The condition primarily affects captive-bred tarantulas, especially when terrarium hygiene is poor or when contaminated prey is offered.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
Signs in the Goliath birdeater are subtle and nonspecific, making detection difficult for an untrained owner.
A decrease or complete loss of appetite may be observed, sometimes lasting several weeks.
The animal may appear sluggish, less responsive, and remain motionless in one corner of the terrarium.
Progressive weight loss is possible, particularly visible through the abdomen (opisthosoma), which appears smaller or flaccid.
Abnormally loose droppings may be found in the terrarium, and in some cases small worms may be visible to the naked eye or under magnification.
These symptoms are not specific to parasitism and may suggest other conditions, making specialist evaluation important.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
The condition results from the presence of nematodes (roundworms) in the tarantula's digestive tract.
These parasites may be ingested through live prey (crickets, cockroaches, other insects) that themselves carry larvae, or through terrarium substrate contaminated with parasite eggs.
Cross-contamination between multiple tarantulas sharing non-disinfected equipment is also possible.
A poorly maintained terrarium with substrate that is rarely changed favors the persistence of parasite eggs in the environment.
Feeding live prey raised in poor sanitary conditions or captured in the wild increases the risk of contamination.
Failure to quarantine a newly introduced tarantula or new food insects before adding them to the collection is a risk factor.
General weakness in the animal—for example after a difficult molt—can increase vulnerability.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Diagnosis in tarantulas remains challenging because standard veterinary tools are poorly suited to their anatomy.
A veterinarian specializing in exotic animals can examine feces found in the terrarium under a microscope to look for eggs or worms.
Direct observation of the animal, its eating behavior, and its weight over time also form part of the evaluation.
In some cases, more detailed examination may be offered, but remains limited by constraints specific to invertebrates.
Treatment
Management relies on antiparasitic agents specific to invertebrates, used only on prescription and under the supervision of a veterinarian experienced with exotic animals.
Support measures may be combined with this, such as improving terrarium hygiene conditions and the animal's hydration.
No treatment should be given without professional advice, as dosing in invertebrates is extremely delicate and the risk of toxicity is significant.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention centers above all on terrarium hygiene: regular substrate changes, cleaning and disinfection of equipment between animals.
It is recommended to use only prey from reliable breeders and to quarantine any new prey or new animal before introducing it to your collection.
Avoiding wild-caught insects significantly reduces the risk of parasite introduction.
Routine checks by a veterinarian specializing in invertebrates can be considered for large collections.
Possible complications
Heavy infestation that goes untreated can lead to marked weakness in the tarantula, progressive malnutrition, and in severe cases, death of the animal.
Chronic parasitism can also complicate molting, already a fragile period for these animals.
When to see a veterinarian
The animal refuses to eat for an unusually long period.
Worms are visible in the feces or terrarium substrate.
The tarantula's abdomen appears abnormally reduced or flaccid.
The animal seems unusually lethargic or remains immobile for an extended period.
Soft or watery feces persist in the terrarium.
Prognosis
Prognosis depends on the degree of infestation and how quickly treatment is started.
Light infestation detected early and treated by a specialist has a good chance of favorable outcome.
Conversely, delayed diagnosis or heavy infestation can compromise the animal's survival, especially due to the slow metabolism of tarantulas, which makes it difficult to track disease progression.
Frequently asked questions
Can you see worms with the naked eye?
In some cases yes, especially if they are present in large numbers in the stool, but often examination with a magnifying glass or microscope by a professional is necessary to confirm their presence.
Is this parasitism transmissible to humans or to other domestic animals?
Nematodes of tarantulas are normally specific to invertebrates and are not considered transmissible to humans or domestic mammals.
Can I treat my tarantula myself with an over-the-counter antiparasitic?
No, this is strongly inadvisable. Tarantulas are highly sensitive to many chemical substances and incorrect dosing can be fatal. Specialized veterinary advice is essential.
How can I prevent my other tarantulas from getting contaminated?
It is advisable to quarantine any suspect animal, disinfect all equipment used, and not share prey or substrate between multiple terrariums.
References
AVMA — American Veterinary Medical Association
Content reviewed by the TunisieVet editorial team · Updated 28 August 2026
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