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Spider Envenomation, Tarantula

Author: Scott D Fell, DO, FAAEM, Medical Director, Emergency Care Center, Venice Regional Medical Center
Coauthor(s): Christina L Kukula, DO, Fast Track, Venice Regional Medical Center; Medical Director, Urgent Care Center at The Oaks
Contributor Information and Disclosures

Updated: May 7, 2009

Introduction

Background

Tarantulas are among the largest spiders in the world and likely the most feared. Emergency physicians are increasingly likely to encounter patients who have had tarantula contact as the popularity of tarantulas as pets is increasing.

Tarantulas belong to the suborder Orthognatha and the family Theraphosidae. These large (2.5-7.5 cm) arachnids are slow moving. Females can live as long as 35 years, while the male life span is generally 5-7 years. They have poor eyesight and sense their prey through vibrations. The largest species, Theraphosa blondi, which is found in South America, can have fangs 1 inch long and a leg span up to 12 inches.

Tarantulas generally can be found in tropical and subtropical areas of the world. The largest tarantulas are found in South America. In the United States, great numbers are found in the southwestern states. Most tarantulas sold in pet stores in the United States are imported species of Aphonopelma.

Although tarantulas often evoke panic and anxiety on sight, these hairy long-legged spiders generally are nonaggressive and rarely bite. Tarantulas usually retreat as their main line of defense.

If forced to defend itself, the arachnid may flick very fine, fiberglasslike, sharp, barbed hairs from its abdomen at its enemy (see Media files 1-2). These may stimulate ocular, dermatologic, and respiratory tract irritation. Density of hairs on the abdomen is approximately 10,000 per mm².

Of historical interest is a piece of 14th-century folklore that arose from the Lycosa tarentula (actually a wolf spider) of southern Italy. Certain individuals who thought they had been bitten by this spider would attempt to exhaust themselves by dancing wildly. This condition came to be referred to as tarantism. It has been suggested that the arachnids responsible for these episodes were actually widow spiders of the genus Latrodectus.

Also from the Middle Ages are reports of a dancing mania known as Tanzwuth that was attributed to spider bites.¹ So-called victims would seek out minstrels who would play instruments with shrill tones; this music caused the victims to dance until they fainted. Seizures, demonic possession, and tarantula bites all have been proposed as causes of this behavior. However, no true etiology has been identified, and dancing mania still remains a mystery.

Pathophysiology

Because of the tarantula's forms of defense, human injury is limited mainly to skin and ocular involvement, with occasional respiratory symptoms.

Tarantula venom is rarely toxic to humans; bites from tarantula species in the United States can be painful but are not considered dangerous. The typical effects are no more serious than those of Hymenoptera stings. The most common reaction is a low-grade histamine response.

Envenomations from the funnel web spider of southern and eastern Australia can be dangerous, even fatal (see Spider Envenomations, Funnel Web).

Hairs discharged from the tarantula can penetrate several layers of skin or ocular tissue and cause mechanical irritation. Urticating hair morphology ranges from type I to type IV. Only type I hairs are found in US tarantulas, and these do not penetrate the skin as deeply as other types. Type III hairs can penetrate up to 2 mm, causing inflammation and local reaction. Although not common, inhalation of urticating hairs may cause significant allergic rhinitis. Exposure to hairs of certain species in South America (Grammastola) can suffocate small mammals within 2 hours.

Frequency

United States

Approximately 40 species of tarantula live in the United States. The incidence of tarantula-inflicted injuries is not known.

International

More than 1500 species of tarantula live throughout the world. Outside the United States, tarantulas can be found in Mexico, Central America, South America, the Caribbean Islands, Africa, areas of Europe bordering the Mediterranean Sea, and Australia.

Mortality/Morbidity

While all North American species are relatively harmless, a few species in South America, Africa, and Australia may be dangerous to humans (see Spider Envenomations, Funnel Web).

Clinical

History

• Bites
  • Unprovoked bites are uncommon because tarantulas are usually docile; patients usually are able to tell what has inflicted their injury.
  • Most patients bitten by tarantulas complain of mild pain similar to a pinprick. Some tarantula bites can cause severe pain, local swelling, and numbness.
  • Some patients have reported arthritic stiffness lasting for weeks following bites near joints. No permanent deficits have been reported.
• Skin
  • Symptoms at the site of hair penetration include irritation, severe pruritus, edema, and erythema.
  • Rarely, anaphylaxis may follow such exposure.
• Eye
  • Ocular exposure to tarantula hairs may lead to redness and an itchy or gritty sensation.
  • A careful history may be necessary to identify this cause of ocular symptoms because patients may not relate the symptoms directly to tarantula exposure.
• Respiratory: Significant allergic rhinitis may be present in patients who have inhaled hairs.

Physical

The findings following a tarantula bite closely resemble those of Hymenoptera stings (ie, local swelling and erythema). As noted above, the exception is the bite of the funnel web spider, which is found outside the United States.

• Skin
  • Like insect bites, tarantula bites cause local erythema and edema.
  • Erythema and pruritic papules may be observed in skin exposed to urticating abdominal hairs. This exposure also may lead to an allergic reaction and, rarely, precipitates anaphylaxis.
  • The risk of serious reactions is much higher outside the United States, where spiders with type III and type IV hairs are found.
• Eye
  • Several cases of ocular injuries from discharged hairs have been described in the literature.^2,3,4,5,6,7
  • Patients may have a red eye and associated keratoconjunctivitis. Depending on the depth of hair penetration, patients also may have conjunctival injection or anterior chamber inflammation.
  • Ophthalmia nodosa has been diagnosed in several individuals with resulting panuveitis that still was clinically active up to 72 months following the initial diagnosis.^6,2
  • Multiple fine intracorneal hairs may be observed on slit-lamp examination; however, they may be elusive because of their small size and location.
  • The right eye is affected more commonly than the left eye in patients who are right-hand dominant and handle tarantulas.
• Respiratory: Allergic rhinitis signs and symptoms may be present if a patient has inhaled urticating hairs.

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