Spider Mite Infectious Stomatitis (Mouthrot)

What is it?

Infectious stomatitis, commonly called "mouthrot," is an infection affecting the mouth and oral parts of the Goliath birdeater (Theraphosa blondi). It is caused by opportunistic bacteria that take advantage of a small wound or weakened state to develop. This condition is particularly concerning because the spider depends on an intact mouth for feeding, and an untreated infection can quickly threaten the animal's survival.

In spiders, the mouth region includes the chelicerae (venom fangs) and a small mouth opening surrounded by sensory hairs. Any injury in this area, even minor, can become infected if the spider's environment is not appropriate.

Commonly observed signs

These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.

Causes and risk factors

The infection is usually caused by opportunistic bacteria, such as certain Pseudomonas species or other environmental bacteria, which colonize a wound or weakened area of the mouth. These bacteria naturally occur in the enclosure environment, particularly in poorly maintained or overly moist substrates.

An injury to the chelicerae—for example following a fall, rough handling, or a struggle with an overly aggressive prey—can create an entry point for these germs. A weakened immune system brought on by chronic stress, difficult molting, or unsuitable living conditions also favors infection development.

An enclosure that is too humid, poorly ventilated, or infrequently cleaned significantly increases the bacterial load in the environment. Spiders recently injured—for instance after a fall from height or inadequate handling—are more vulnerable.

Stress from an unsuitable environment (incorrect temperature, lack of hiding places, aggressive prey left too long in the enclosure) weakens the animal's natural defenses. Older spiders or recently molted ones, a period when their tissues are more fragile, also face increased risk.

Diagnosis and care

Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.

Treatment

Management is the responsibility of a veterinarian with experience in invertebrates. It may include gentle cleaning of the affected area with appropriate antiseptic solutions and, if necessary, local antibiotic treatment or immersion therapy according to the veterinarian's recommendations.

Nutritional support may be considered if the animal refuses to eat, in the form of careful tube-feeding performed only by a professional. Improving housing conditions is an integral part of care.

Prevention

Possible complications

Without treatment, infection can spread and progressively destroy mouth structures, making feeding impossible. Severe malnutrition can develop within weeks as the animal can no longer feed properly.

In the most severe cases, infection can become systemic and lead to the tarantula's death, particularly if bacteria reach the hemolymph (the invertebrate equivalent of blood).

When to see a veterinarian

Prognosis

The prognosis depends greatly on how early treatment is started. When detected early, the infection can be controlled with appropriate treatment and improved living conditions.

If the infection is advanced and oral structures are already damaged, however, the prognosis becomes guarded, as the animal's ability to feed may be permanently affected.

Frequently asked questions

References

AVMA — American Veterinary Medical Association

Content reviewed by the TunisieVet editorial team · Updated 28 August 2026