The term ‘bug bite’ or ‘insect bite’ is commonly used to denote both bites and stings inflicted by members of the phylum Arthropoda. Notable arthropods possessing stingers include bees, wasps, hornets, fire ants, and scorpions. Most common clinical manifestations of arthropod bites and stings include erythematous and edematous eruptions along with other dermatological findings such as papules and urticaria. The consequences of arthropod bites are generally due to traumatic injury or local inflammation and hypersensitivity to arthropod saliva. Both bites and stings create tissue injury which can serve as a portal of entry for secondary bacterial infection. In some cases, the delivery of toxic venom can result in significant systemic reactions including autonomic instability, neurotoxicity and organ failure. The acute development of anaphylactic reactions can be fatal, most commonly due to angioedema or circulatory collapse. The most clinically significant impact of arthropod bites is their ability to serve as vectors for numerous bacterial, viral, and protozoal diseases.
Chilopods
Centipedes are chilopods characterized by a cephalad biting structure connected to a venom gland. Bites often produce two hemorrhagic punctures accompanied by surrounding erythema and swelling. The venom consists of biochemical mediators, including metalloproteases, which result in immediate localized pain. Treatment is generally supportive and includes cleaning the area with soap and water, local application of ice, topical steroids, and pain management with analgesics.
Diplopods
Millipedes are members of the class Diplopoda, characterized by the presence of two pairs of legs per body segment. Millipedes inflict damage through secretion of a toxic liquid from glands on the sides of their body segments which produces a localized caustic-like effect to tissues. Clinically this may present with an intense burning sensation accompanied by erythema and occasionally vesicle formation. The toxic liquid often causes the development of a localized area of hyperpigmentation, usually brown or black, which may last for months. Treatment of topical exposure includes topical antibiotics and analgesics. Washing the area immediately with soap water following exposure may help reduce the effects of the toxin.
Bedbugs
Cimex lectularius, the human bedbug, is an obligate blood feeder with a worldwide distribution. It is oval shaped, flat, red-brown in color and about 3 to 6 mm in length. Bedbugs usually live in crevices in walls, floors, mattresses, cushions, bed frames, and other structures. Bites sometimes occur linearly and most commonly manifest as a small papule or punctum usually without a surrounding reaction. Treatment of bites consists primarily of symptomatic care with the use of topical corticosteroids and systemic antihistamines to control pruritus. Secondary infections should be treated with the appropriate antibiotics. Elimination of infestations can be difficult and requires a combination of professionally applied insecticide and nonchemical controls.
Kissing Bugs
Kissing bugs, or triatome bugs, are a type of reduviid bug that can carry the parasite Trypanosoma cruzi, the etiologic agent of Chagas disease. Kissing bugs are 1.5 to 2.5 cm long, brown or black and typically have red or yellow stripes on their abdomen. Triatomes are blood-sucking insects and nocturnal feeders which transmit Trypanosoma cruzi through their feces. Their range runs in the southern United States, Mexico, Central America and South America where they typically live in thatched roofs or cracks and holes of substandard housing. Victims may sometimes inadvertently scratch or rub the feces into the bite wound or the mucous membranes, especially the eyes or mouth. Bites are usually painless and present as papules with hemorrhagic puncta or vesiculobullous lesions. An area of localized swelling, erythema, and induration corresponding to the site of trypanosome entry is known as a chagoma. The classic finding in acute Chagas disease is the presence of a chagoma on the eyelid, known as Romana’s sign. Following the acute phase of the infection, which can last for several months, patients enter the chronic phase, during which the infection may remain asymptomatic for decades. Approximately 20 to 30% of infected patients will develop cardiac or gastrointestinal complications.
Flies
There are a number of medically significant flies that bite humans, most notably the deer fly, horse fly, sand fly, and tsetse fly. When obtaining a blood meal, flies use their specially designed mouthparts to lacerate the skin, inject its anticoagulant-containing saliva and then suck up the resulting bleeding. Some flies can transmit serious diseases such as the Tsetse fly (Glossina sp.) which transmits African trypanosomiasis, the sand fly (Phlebotomus sp.; Lutzomyia sp.) which transmits bartonellosis and leishmaniasis, and the deer fly (Chrysops sp.) which transmits Loa loa and tularemia. The black fly (Simulium sp.) can transmit onchocerciasis and mansonellosis, while horse fly (family Tabanidae) can also transmit several filarial worms. Fly bites are usually quite painful and may produce significant cutaneous inflammation and the development of large urticarial wheals and papules. Treatment consists of symptomatic care including ice application, pain control with acetaminophen or NSAIDs, thorough washing of the wound, and systemic antihistamines for itching.
Myiasis is a condition that occurs when there is an infestation of fly larvae, particularly the human botfly. Transmission usually occurs when a female fly lays eggs directly on a blood-sucking insect such as a mosquito. When the insect lands and bites its victim, the eggs get deposited on the skin, hatch, and the larvae quickly burrow under the skin and emerge fully mature after 5 to 10 weeks. Wound myiasis occurs when flies deposit larvae on or near a wound where they feed on the surrounding tissue. Copious irrigation will usually remove the larvae, but sometimes debridement is required.
Hymenoptera
The order Hymenoptera includes wasps, bees, yellow jackets, hornets and fire ants. These insects all have a painful sting delivered by their venom-injecting caudal stinger. The composition of these venoms is complex, and some have the potential for cross-sensitization. Local reactions to stings are most common and present with an immediate onset of localized pain, erythema and edema. Anaphylactic reactions may present with the initial symptoms of pruritus, facial flushing, and urticaria which can rapidly progress to wheezing, dyspnea, angioedema and stridor, vomiting, abdominal cramping, and syncope. The Apidae family of Hymenoptera, consisting of honeybees and bumblebees, possess a stinger with curved barbs which remains in the victim following a sting. Wasps and yellow jackets comprise the Vespidae family which, unlike members of the Apidae family, do not lose their stinger in an attack and have the ability to sting multiple times. Treatment of uncomplicated stings includes manual remover of the stinger, application of ice compresses, and analgesics for pain. Short courses of systemic antihistamines and corticosteroids are effective for more severe localized reactions.
Fire ants are Hymenoptera belonging to the Formicidae family. They may be red or black, are very aggressive, and often attack in swarms. Fire ants begin their attack by latching on to their victim with powerful jaws and then deliver up to 10 stings with their ovipositor. Their venom is composed of alkaloids and causes intense, burning-like pain. Their venom may produce anaphylaxis and has potential crossover sensitization with other Hymenoptera venom. As with the Vespidae and Apidae families, most reactions consist of localized dermatologic findings. The presence of two central hemorrhagic puncta from the bite of the ant, surrounded by a ring of erythematous papules caused by the sting, is a distinctive characteristic. These papules develop into vesicles and then sterile, pruritic pustules over 6 to 24 hours. Treatment is similar to that of other Hymenoptera stings.
Fleas
Fleas are wingless ectoparasites that feed on mammals and birds. They are 2 to 4 mm long, thin, and are red to brown. Fleas are holometabolous insects, going through the four lifecycle stages of egg, larva, pupa, and imago (adult). In most species, neither female nor male fleas are fully mature when they first emerge but must feed on blood before they become capable of reproduction Flea bites typically present as erythematous papules, often with a hemorrhagic appearing center. Bites may also manifest as urticarial lesions, vesicles or bullae. The pruritus can be severe, and scratching of the lesions can result in skin excoriation and secondary bacterial infection. The primary goal in treating flea bites is to control the intense itching through the use of topical calamine lotion or corticosteroids, and systemic antihistamines. The most significant medical impact of fleas is their ability to serve as vectors for several serious, and potentially fatal diseases including tularemia, endemic typhus, and bubonic plague. The flea species related to the disease transmission are Xenopsylla cheopis and Pulex irritans.
Ticks
Nymphal and adult ticks are characterized by the presence of eight legs tipped with a pair of claws and an oval-shaped body which becomes engorged during feeding. Most ticks are categorized as hard ticks, belong to the Ixodidae family, or soft ticks belonging to the Argasidae family. Ticks feed by cutting a hole in the epidermis and injecting anticoagulants or compounds which inhibit platelet aggregation. Tick bites are usually painless and can present with a wide variety of rashes and other dermatologic findings, making diagnosis challenging. Bites often appear as an erythematous papule with surrounding erythema while others may present as pruritic urticarial lesions. The most significant impact of ticks on humans is their ability to serve as vectors for significant diseases including Rocky Mountain spotted fever, endemic typhus, ehrlichiosis, Q-fever, encephalitis, hemorrhagic fever, Lyme disease, relapsing fever, tularemia, babesiosis. Uncomplicated tick bites are treated with routine wound care, topical corticosteroids and systemic antihistamines for pruritic lesions and antibiotics if secondary infection is present. Ticks should be removed with fine-tipped tweezers.
Scorpions
Scorpions are large arachnids with a pair of anterior legs possessing pinchers. Their tail-like structure containing a stinger and two venom glands. Most stings produce only localized pain similar to that of Hymenoptera stings. While systemic symptoms are uncommon, the venom from the bark scorpion can cause several adverse autonomic and motor effects such as hypertension, tachycardia, tachydysrhythmias, myoclonus, and fasciculations. The diagnosis of scorpion envenomation generally relies on a history of a scorpion sting, presence in a scorpion endemic region and characteristic findings of envenomation. Except in the case of children, most stings manifest similarly to Hymenoptera stings and can be managed with supportive care including removing the stinger if present, cleaning the site with soap and water, ice application to the area and acetaminophen for pain. Systemic symptoms such as agitation, muscle spasms and myoclonus require further medical attention.
Spiders
The two spiders that have the greatest potential to cause significant morbidity are the Black Widow and Brown Recluse. Black Widows are spiders from the genus Latrodectus, with the most well-known being the North American black widow, Latrodectus mactans. They are approximately 1.5 cm in length and have up to a 4 cm leg span. Widow spiders are dark brown or black with a rounded, shiny abdomen and are most widely recognized for the presence of a red or orange hourglass on the ventral surface of their abdomen. Most bites are defensive, occurring when the female spider perceives a threat to herself or her eggs, or when the spider is unintentionally disturbed. While the black widow has potentially dangerous venom, many bites result in only minimal symptoms and produce no severe damage. Perception of the bite is usually as a sharp pinprick-like sensation which may develop into a dull ache or numbness at the site. Two red puncta may be visible, and surrounding erythema may appear within 60 minutes of the bite. Other clinical manifestations may include hypertension, sweating, salivation, restlessness, fasciculation, ptosis, nausea, vomiting, and dyspnea. Severe symptoms usually occur within 1 to 6 hours and last anywhere from 12 to 48 hours. The venom of the black widow spider is most notable for the potent neurotoxin, alpha-latrotoxin, which unlike the brown recluse, does not cause local necrosis. Management for those without systemic symptoms is with supportive care including washing the bite site, application of an ice pack to the area, and treatment of pain with analgesics.
Brown Recluse spiders (Loxosceles reclusa) are approximately 1 to 1.5 cm in length with a leg span of greater than 2.5 cm. They have a yellow to brown cephalothorax, a tan abdomen, and possess a violin-shaped marking on their dorsal cephalothorax which accounts for its nickname, the “fiddle-back” spider. They are predominantly found in the south and the central United States. Bites typically occur on the extremities when the spider’s dwelling is disturbed, or it feels threatened. Bites may be perceived as a sharp, stinging sensation but are often painless and cause only minor, inconsequential reactions, usually presenting as small erythematous lesions. Some bites will develop an area of cyanosis or pallor, sometimes with the appearance of hemorrhagic blisters, due to tissue ischemia. The most common complication in serious envenomations is full thickness skin necrosis. Diagnosis of uncomplicated brown recluse bites may be difficult as the initial bite is often painless, and the spider may go unseen. Diagnosis is usually based on the history, especially if the spider was seen, in conjunction with the presence characteristic dermatologic findings. In uncomplicated bites, treatment consists of routine wound care and local application of ice which may decrease the activity of damaging enzymes found in the venom.
Chiggers
Chiggers are tiny red mite larvae, measuring 0.3 to 1.0 mm in length, belonging to the Thrombiculidae family. Encounters with chiggers tend to be in tall grasses, weeds, and in woodlands. Infestations occur when mite larvae feed on human skin, predominantly in areas where they reach a constricting area of clothing such as at the ankles, thigh or waist. Bites are usually not felt initially, but an allergic reaction to the mite saliva causes the development of extremely pruritic red papules which later develop into eschar lesion. Mites are visible on the skin as tiny red dots that will often crawl until reaching an area of clothing-skin interfaces such as the top of a sock or the belt-line of pants. The primary treatment is to control the intense itching with topical calamine lotion or corticosteroids and systemic antihistamines. Chiggers are vectors for Scrub Typhus in some parts of Asia, Russia, and islands of the Indian and the Pacific Oceans.
The most important step towards reducing the clinical impacts of arthropod bites and stings is to prevent them from occurring in the first place. Most available methods focus on the prevention of bites from mosquitoes and ticks, which transmit the vast majority of vector-borne pathogens to humans. The major prevention efforts involves the use of effective insect repellents containing DEET (N, N-diethyl-meta-toluamide). Concentrations of 20 to 50% are recommended and can provide up to several hours of protection from mosquitoes and ticks. Appropriate clothing such as light colored pants, long-sleeved shirts, and hats also reduce the likelihood of sustaining insect bites and contracting vector-borne diseases.
References:
Alpern JD, Dunlop SJ, Dolan BJ, Stauffer WM, Boulware DR. Personal Protection Measures Against Mosquitoes, Ticks, and Other Arthropods. Med Clin North Am. 2016;100(2):303-16.
Erickson TB, Cheema N. Arthropod Envenomation in North America. Emerg Med Clin North Am. 2017;35(2):355-75.
Haddad V, Jr., Cardoso JL, Lupi O, Tyring SK. Tropical dermatology: Venomous arthropods and human skin: Part I. Insecta. J Am Acad Dermatol. 2012;67(3):331.e1-14; quiz 45.
Haddad V, Jr., Cardoso JL, Lupi O, Tyring SK. Tropical dermatology: Venomous arthropods and human skin: Part II. Diplopoda, Chilopoda, and Arachnida. J Am Acad Dermatol. 2012;67(3):347.e1-9; quiz 55.
Juckett G. Arthropod bites. Am Fam Physician. 2013;88(12):841-7.
Quan D. North American poisonous bites and stings. Crit Care Clin. 2012;28(4):633-59.
Steen CJ, Carbonaro PA, Schwartz RA. Arthropods in dermatology. J Am Acad Dermatol. 2004;50(6):819-42, quiz 42-4.
Powers J, McDowell RH. Insect Bites [Updated 21 May 2019]. Treasure Island, FL, StatPearls Publishing. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537235/.
Vasievich MP, Villarreal JD, Tomecki KJ. Got the Travel Bug? A Review of Common Infections, Infestations, Bites, and Stings Among Returning Travelers. Am J Clin Dermatol. 2016;17(5):451-62.
