Tarantula Envenomation 

Updated: Jun 19, 2020
Author: Scott D Fell, DO; Chief Editor: Joe Alcock, MD, MS 

Overview

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.[1] 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 (shown in the images below). These may stimulate ocular, dermatologic, and respiratory tract irritation. Density of hairs on the abdomen is approximately 10,000 per mm2.

The Chilean rose tarantula. The urticating hairs a The Chilean rose tarantula. The urticating hairs are clearly visible. Courtesy of Mike Dembinsky.
Enlargement of tarantula hairs. Courtesy of Cara S Enlargement of tarantula hairs. Courtesy of Cara Shillington.

See Venomous Spider Bites: Keys to Diagnosis and Treatment, a Critical Images slideshow, for help identifying and treating various envenomations.

A tarantula may bite, but first assumes a strike position by raising its front pair of legs and rearing back on its abdomen.

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.[2]

Also from the Middle Ages are reports of a dancing mania known as Tanzwuth that was attributed to spider bites.[3] 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.[4] The typical effects are no more serious than those of Hymenoptera stings.[5] The most common reaction is a low-grade histamine response.[6]

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

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.

Epidemiology

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.

Prognosis

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

Experience with ocular injuries is somewhat limited, and more information is necessary for accurate conclusions regarding long-term prognosis.

Recovery from eye injuries may be prompt but has been delayed up to 72 months.

No cases of infection from tarantula bites or skin exposure to urticarial hairs have been reported; therefore, prophylactic antibiotics are not recommended.

Patient Education

As tarantulas become increasingly popular as pets, owners need to be aware of the potential injuries that can occur.

Discourage frequent and routine handling of tarantulas. Handlers should wear gloves, avoid tarantula contact with their face and eyes, and wash their hands after working with tarantulas.

For patient education resources, see the First Aid and Emergencies Center as well as the patient education articles, Black Widow Spider Bite and Brown Recluse Spider Bite.

 

Presentation

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.[7]

Respiratory

Significant allergic rhinitis may be present in patients who have inhaled hairs.

Physical Examination

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.[8, 9, 10, 11, 12, 13]

Patients may have a red eye[14] 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.[8, 12]

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.

Complications

Ophthalmia nodosa and panuveitis can complicate ocular exposure to tarantula hairs.

 

DDx

 

Workup

Laboratory Studies

No specific diagnostic studies, laboratory tests, or imaging studies are helpful in the evaluation and treatment of patients with injuries inflicted by tarantulas.

Procedures

Careful slit-lamp biomicroscopic examination is indicated for a patient presenting with ocular concerns. Examination with fluorescein is then also indicated. Look for tortuous vessels at the limbic margin and presence of flare or cells in the anterior chamber, findings that can indicate an anterior uveitis. Examine for central infiltrates as shown below.

Slit-lamp photograph showing 2 central infiltrates Slit-lamp photograph showing 2 central infiltrates caused by urticating tarantula hairs (arrows). Courtesy of Southern Medical Journal and David A. Belyea, MD.
 

Treatment

Prehospital Care

Capture the offending arachnid for identification if it is possible to do so safely.

Begin supportive therapy for patients who are having a rare allergic reaction or anaphylaxis.

Following ocular exposure, place a protective shield over the eyes to prevent the patient from rubbing the eyes and possibly driving hairs deeper.

Emergency Department Care

A patient with anaphylaxis or allergic reaction requires prompt supportive care and attention to the ABCs.

In patients with severe reaction, establish an intravenous line, provide supplemental oxygen, and place them on a cardiac monitor.

Skin

Protect areas of localized dermatitis and allergic reactions with appropriate local wound care, including wound cleansing and ice to decrease inflammation.

Determine tetanus immunization status and provide prophylaxis as needed.

Treat pruritus and erythema with antihistamines and corticosteroids.

Administer parenteral or enteral analgesics to relieve severe pain.

Eye

Ocular injury caused by tarantula hairs can be complicated and requires ophthalmologic consultation.

After initial evaluation, patients should be treated with a topical broad-spectrum antibiotic.

Topical steroids are required for patients with panuveitis or keratoconjunctivitis; they should be prescribed only after consultation with an ophthalmologist.

As with skin contact, tetanus prophylaxis is indicated when the eye is involved.

Medical Care

Patients with local dermatitis caused by urticating hairs should be discharged from the ED with a course of oral corticosteroids (eg, prednisone) and an antihistamine such as cetirizine (Zyrtec) or diphenhydramine (Benadryl).

Cetirizine may be preferred because of its lower incidence of anticholinergic adverse effects and the convenience of once-a-day dosing. The drawback of cetirizine is its higher cost.

A prescription for oral analgesics also should be provided.

Local skin wounds from tarantula bites or urticating hairs should be re-examined in 48 hours; patients should be educated regarding the signs and symptoms of infection.

Patients with ocular involvement should be seen by an ophthalmologist as soon as possible (< 24 h).

Consultations

Patients can develop long-term inflammatory changes in the eye exposed to tarantula hairs, and definitive diagnosis of retained hairs cannot always be made by routine ED slit-lamp examination. Consulting an ophthalmologist is mandatory in such exposures.

Prevention

Tarantula bites can be avoided almost completely by not attempting to handle or harass these arachnids. Wearing gloves when gardening and being cautious about hand placement can prevent accidental bites.

 

Medication

Medication Summary

No existing medications are specific to treat tarantula injuries occurring in the United States. Medical therapy is directed mainly at symptom relief.

One species of the funnel web spider (Atrax robustus) of Australia produces highly toxic venom that is neurotoxic and potentially fatal. Antivenom specific to Atrax has been developed and is used in Australia.

Antihistamines

Class Summary

Antihistamines prevent but do not reverse histamine-mediated responses, particularly in smooth muscle of the bronchi, GI tract, uterus, and blood vessels. They prevent histamine responses in sensory nerve endings. Antihistamines are commonly used for temporary relief of symptoms caused by allergic conditions.

Diphenhydramine (Benadryl)

Diphenhydramine competes with histamine for cell receptor sites on effector cells; it has anticholinergic (drying) and sedative adverse effects.

Cetirizine (Zyrtec)

Cetirizine forms a complex with histamine to block H1-receptor sites on target cells in the blood vessels, GI tract, and respiratory tract.

Corticosteroids

Class Summary

Corticosteroids modify the body's immune response to diverse stimuli. They suppress the migration of polymorphonuclear (PMN) leukocytes and reverse increased capillary permeability, reducing inflammatory processes. Corticosteroids can cause profound and varied metabolic effects.

Prednisone (Deltasone, Sterapred, Orasone)

Prednisone has potent antiinflammatory effects in disorders of many organ systems.

Ophthalmic agents

Class Summary

Ophthalmic agents are used for inflammatory conditions in which corticosteroids are indicated and risk of infection exists.

Neomycin/polymyxin B/bacitracin topical (Cortisporin)

Hydrocortisone suppresses the inflammatory response. Because it also may inhibit the body's defense mechanism against infection, a concomitant antimicrobial drug may be used, giving rationale for the combination. Anti-infective components are included to provide action against specific susceptible organisms.