What’s Eating You? Triatoma and Arilus cristatus Bugs

Classification

Triatomine bugs (Triatoma) and the wheel bug (Arilus cristatus) are part of the family Reduviidae (order Hemiptera, a name that describes the sucking proboscis on the front of the insect’s head).^1,2 Both arthropods are found in multiple countries and are especially common in warmer areas, including in the United States, where they can be seen from Texas to California.^3,4 Because blood-feeding triatomines need a blood meal to survive while laying eggs and then throughout their 5 developmental nymph stages to undergo molting, they feed on mammals, such as opossums, raccoons, pack rats, and armadillos, whereas wheel bugs mainly prey on soft-bodied insects.^1,4-6

Triatoma bugs seek cutaneous blood vessels using thermosensors in their antennae to locate blood flow under the skin for feeding. After inserting the proboscis, they release nitric oxide and an anticoagulant that allows for continuous blood flow while feeding.⁷ It has been reported that triatomine bugs are not able to bite through clothing, instead seeking exposed skin, particularly near mucous membranes, such as the hands, arms, feet, head, and trunk. The name kissing bug for triatomines was coined because bites near the mouth are common.⁶ The bite typically is painless and occurs mainly at night when the insect is most active. After obtaining a blood meal, triatomine bugs seek shelter and hide in mud and daub structures, cracks, crevices, and furniture.^1,8

Unlike Triatoma species, A cristatus does not require a blood meal for development and survival, leading it to prey on soft-bodied insects. Piercing prey with the proboscis, wheel bugs inject a toxin to digest the contents and suck the digested contents through this apparatus.⁴ Because the wheel bug does not require a blood meal, it typically bites a human only for defense if it feels threatened. Unlike the painless bite of a triatomine bug, the bite of A cristatus is extremely painful; it has been described as the worst arthropod bite—worse than a hornet’s sting. The pain from the bite is caused by the toxin being injected into the skin; possible retention of the proboscis makes the pain worse.^4,9 In addition, when A cristatus is disturbed, it exudes pungent material from a pair of bright orange subrectal glands while stridulating to repulse predators.⁹

Although Triatoma species and A cristatus have separate roles in nature and vastly different impacts on health, they often are mistaken for the same arthropod when seen in nature. Features that members of Reduviidae share include large bodies (relative to their overall length); long thin legs; a narrow head; wings; and a long sucking proboscis on the front of the head.¹⁰

FIGURE 1. Triatomine bug (so-called kissing bug)(Triatoma species).

Characteristics that differentiate Triatoma and A cristatus species include size, color, and distinctive markings. Most triatomine bugs are 12- to 36-mm long; are dark brown or black; and have what are called tiger-stripe orange markings on the peripheral two-thirds of the body (Figure 1).¹¹ In contrast, wheel bugs commonly are bigger—measuring longer than 1.25 inches—and gray, with a cogwheel-like structure on the thorax (Figure 2).¹⁰

FIGURE 2. Wheel bug (Arilus cristatus).

Dermatologic Presentation and Clinical Symptoms

The area of involved skin on patients presenting with Triatoma or A cristatus bites may resemble other insect bites. Many bites from Triatoma bugs and A cristatus initially present as an erythematous, raised, pruritic papule with a central punctum that is visible because of the involvement of the proboscis. However, other presentations of bites from both arthropods have been reported^4,6,7: grouped vesicles on an erythematous base; indurated, giant, urticarial-type wheels measuring 10 to 15 mm in diameter; and hemorrhagic bullous nodules (Figure 3). Associated lymphangitis or lymphadenitis is typical of the latter 2 variations.⁶ These variations in presentation can be mistaken for other causes of similarly presenting lesions, such as shingles or spider bites, leading to delayed or missed diagnosis.

FIGURE 3. A well-circumscribed wheal with erythematous serpiginous borders and central punctum, secondary to a bite by a Triatoma bug.

Patients may present with a single bite or multiple bites due to the feeding pattern of Triatoma bugs; if the host moves or disrupts its feeding, the arthropod takes multiple bites to finish feeding.⁸ In comparison, 4 common variations of wheel bug bites have been reported: (1) a painful bite without complications; (2) a cutaneous horn and papilloma at the site of toxin injection; (3) a necrotic ulcer around the central punctum caused by injected toxin; and (4) an abscess under the central punctum due to secondary infection.⁴