See original question here.

ANSWER: Assassin Bugs

Assassin bugs might also be known as ambush bugs, wheel bugs, or North American wheel bugs.

The milkweed assassin bug (Zelus longipes; see Image 1) and the wheel bug (Arilus cristatus; see Image 2) are two types of assassin bugs you might find in your garden across North America. They are “true bug” members of the Hemiptera, because they have liquid sucking mouth parts, have a nymph stage in their development, and have six legs and three body parts. They are two of the 160 types of the Reduviidae family of insects found worldwide.

Image 1: The milkweed assassin bug (Zelus
longipes). (Click to enlarge.)

These two types (and others like them) are primarily beneficial bugs to agriculture, eating insects that cause harm to crops—including flies, mosquitos, roaches, beetles, aphids, armyworms, and caterpillars.

They aggressively eat these insects by grabbing them and using their rostrum (a three-jointed spear-like hollow mouth) to stab into prey, even when covered in “armor.” They inject a venom mixture containing a paralytic, which immobilizes prey in about 30 seconds and liquifies their insides. The bugs begin digestion of the prey’s internal nutrient-containing structures, which they suck out though their mouth-straw.

Identifying Common Assassin Bugs

Adult wheel bugs are usually 33-38 mm long, grey colored, have segmented antennae sprouting from a narrow head, and have a distinctive cog-wheel shaped armor on the dorsum of its prothorax with eight to 14 projections— hence “wheel bug.”¹ The wheel bug also has bright orange scent-sacs on its posterior thorax that can release a pungent scented liquid when disturbed.²

Image 2: The wheel bug (Arilus cristatus). (Click to enlarge.)

Adult milkweed assassin bugs—also called the long-legged assassin bug or the Zelus assassin bug—are 16-18 mm in length, have orange coloration with white spots on the thorax, long segmented antennae extending from a narrow head, and have a business-end sharp rostrum designed for stabbing.

Another subfamily of assassin bugs are “kissing bugs” (triatomine). In contrast to the previously described garden-group of assassin bugs, these are blood-feeding, have much smaller rostrums, and eat through an essentially painless poke. They bite people’s faces at night without waking them up. While they are drinking blood, the insect produces stool that is infected and full of the protozoan parasite Trypanosoma cruzi. This pathogen gets rubbed into the itchy wound producing Chagas disease in the victim.

Toxicological Importance

Normally, the garden variety assassin bugs have no interest in humans and prefer to hide. However, when disturbed and handled, they can inflict a painful response. Although repeatedly referred to as a “bite” in the literature, the injury actually occurs through a stab of your skin by their needle-like rostrum and a dose of their defensive/digestive product—described as “10 times worse” than stings from bees, wasps, or hornets. The sensation has been described as a burning, very sharp pain that can be followed by numbness in the local area for several days.

The local skin area reactions vary from focal pain and redness; to broad areas that are reddened, urticarial, and hot; to punctum-associated abscesses. Broad rash and anaphylaxis have been described in patients sensitized from previous bites.³ Healing times vary but may take two weeks or longer for full resolution.

Dr. Hall described in detail the effects of two “bites” to the right fifth digit of his 10-yearold daughter from Arilus c.⁴ The bite pain was described by her as a “bee” sting. The wound later developed horn-like “papillomata” at the punctures, and compared with her other digits, the affected finger “still was warmer than the others a year later.” More recent investigations into assassin bug venom—specifically in bee-killer assassin bug (Pristhesancus plagipennis)— revealed the production of two separate venoms (one for paralysis and digestion, and one for producing pain for defense) from two distinct groups of glands.⁵

Treatment

There is no antidote. Treatment of A. cristatus and other assassin bug stings depends on the reaction to the insult. Local reaction treatments are generally treated supportively with local corticosteroids and antihistamines. If more generalized allergic reactions occur, treat with standard oral antihistamines and steroids. Anaphylaxis treatment is again standard, with epinephrine and intravenous antihistamines as indicated. Infected bites should be treated with antibiotics, and abscesses incised and drained.^6,7

Dr. Hack is chief of the division of medical toxicology and vice chair for research at East Carolina University in Greenville, N.C.

References

   
1. Smith FD, Miller NG, Carnazzo SJ, Eaton WB. Insect bite by Arilus cristatus, a North American reduviid. AMA Arch Derm. 1958;77(3):324-330.
2. Froeschner RC. Contributions to a synopsis of the Hemiptera of Missouri, Pt. III. American Midland Naturalist. 1944;31:638-683.
3. Boswell ND, Elston DM. What‘s eating you? Triatoma and Arilus cristatus bugs. Cutis. 2023;111(6):289-291.
4. Hall MC. Lesions due to the bite of the wheel-bug, Arilus cristatus (Hemiptera; Reduviidae). Arch Intern Med (Chic). 1924;33(4):513-515.
5. Walker AA, Mayhew ML, Jin J, et al. The assassin bug Pristhesancus plagipennis produces two distinct venoms in separate gland lumens. Nat Commun. 2018;9:755.
6. Moffitt JE, Venarske D, Goddard J, et al. Allergic reactions to Triatoma bites. Ann Allergy Asthma Immunol. 2003;91:122-128.
7. Burnett JW, Calton GJ, Morgan RJ. Triatoma: the “kissing bug”. Cutis. 1987;39(5):399.