Arizona is home to several red and black bugs, and most of them are harmless seed-feeding insects that show up in large numbers during warm months. The most likely culprits are boxelder bugs, red-shouldered bugs (also called soapberry bugs), or one of several seed bug species. There is one red and black bug worth taking seriously, though: the kissing bug, which can carry a disease-causing parasite.
Boxelder Bugs
Boxelder bugs are the most common red and black bugs in Arizona. They belong to the true bug order (Hemiptera) and feed on seeds from boxelder trees. You can identify them by the three bright red lines on the thorax (the segment behind the head) and additional red markings on the wings. Adults are roughly half an inch long and flat-bodied.
These bugs tend to appear in large numbers after very hot summers. They’re drawn to landscapes with lots of seed-producing trees and shrubs. While they’re not harmful to people or pets, they become a nuisance in fall when they swarm the sides of buildings looking for warm spots to spend the winter. They don’t bite, don’t damage structures, and don’t reproduce indoors.
Red-Shouldered Bugs (Soapberry Bugs)
Red-shouldered bugs look almost identical to boxelder bugs at first glance, which makes them one of the most commonly misidentified insects in Arizona. The key difference: red-shouldered bugs have only two red lines on the thorax instead of three, and their overall body color is a darker charcoal gray. Their preferred food source is soapberry trees, golden rain trees, and chinaberry trees rather than boxelders.
The nymphs (immature bugs) are bright red with black legs and antennae. As they mature, the head, thorax, and wing pads darken to near-black. There are typically two generations per year. Females lay eggs in the soil under host trees in spring, nymphs hatch about two weeks later, and adults appear by July. A second generation matures in fall and overwinters in plant debris or inside homes. Like boxelder bugs, they cause no real damage to the trees they feed on and pose no threat to people.
Milkweed Bugs
If the bug you found has bold orange-red and black markings and was near milkweed or oleander plants, it’s likely a milkweed bug. Arizona has both large and small milkweed bug species. New adults are yellow with black markings, but the yellow areas shift to reddish-orange as the bug matures. Nymphs start out as tiny, elongate red insects and become increasingly spotted as they grow through five molts.
Milkweed bugs feed almost exclusively on milkweed seeds, though they’ve also been found on oleander. Their bright coloring is a warning signal to predators: milkweed contains toxic compounds, and bugs that feed on it absorb enough to taste terrible to birds and lizards. They’re completely harmless to people and homes.
Charcoal Seed Bugs
Another common lookalike is the charcoal seed bug (sometimes called the black and red seed bug). These are frequently confused with both boxelder bugs and red-shouldered bugs. They belong to a different family of seed bugs and are found in landscapes with abundant seed-producing plants. Like the others, they feed on seeds and plant sap and pose no danger.
Velvet Ants
If what you saw was fuzzy rather than flat, it’s probably a velvet ant. Despite the name, velvet ants are actually wingless female wasps. They’re covered in dense, velvety hair that’s often bright red or orange on top with a black body. They’re solitary, ground-dwelling, and most active during cooler daylight hours, especially late afternoon.
Velvet ants are not aggressive, but females can deliver an extremely painful sting if handled or stepped on. The sting is rarely dangerous, just memorably unpleasant. They also make a squeaking sound when disturbed by rubbing segments of their abdomen together. The best approach is to leave them alone or gently relocate them. Never pick one up with bare hands or walk barefoot in areas where you’ve seen them.
Kissing Bugs: The One to Watch For
Kissing bugs are the one red and black bug in Arizona that warrants real attention. They’re larger than the seed bugs described above, ranging from half an inch to over an inch long. They’re dark brown or black with reddish or brownish-red markings along the edges of the abdomen, visible just outside the folded wings. Unlike the flat, oval seed bugs, kissing bugs have a more elongated, cone-shaped head.
The concern with kissing bugs is Chagas disease. These insects feed on blood at night, typically biting people on the face while they sleep. They can carry a parasite called Trypanosoma cruzi, which causes Chagas disease. In Arizona, up to half of wild kissing bugs that have been collected and tested carry this parasite. Infection happens not from the bite itself but when the bug defecates near the bite wound and the parasite enters through broken skin or mucous membranes. Chagas disease can cause serious heart and digestive problems years after infection if untreated.
How to Tell Them Apart
The simplest way to sort these bugs:
- Flat, shield-shaped, half-inch long, found on walls or near trees: boxelder bug, red-shouldered bug, or charcoal seed bug. Count the red lines on the thorax. Three lines means boxelder bug. Two lines means red-shouldered bug.
- Bold orange-red and black pattern, found near milkweed or oleander: milkweed bug.
- Fuzzy, ground-dwelling, moves quickly: velvet ant. Don’t touch it.
- Over half an inch, elongated head, reddish edges on the abdomen: kissing bug. Worth identifying carefully.
Keeping Them Out of Your Home
Most red and black bugs enter homes in fall seeking warmth or are drawn to lights at night. A few straightforward changes make a big difference. Seal small cracks and crevices around doors, windows, and foundations with caulk or silicone. Make sure all window screens and vent openings are intact, including pet doors.
Outdoor lighting is a major attractant, especially for kissing bugs during late spring and summer. Switch porch and outdoor lights to yellow bulbs, reduce wattage, or move interior lights away from doors and windows. Clear piles of lumber, firewood, and debris near the house, since these create harborage for both bugs and the rodents that kissing bugs feed on. Removing rodent nests within 300 feet of your home eliminates a key part of the kissing bug life cycle.
For boxelder and red-shouldered bugs specifically, reducing seed litter under host trees and cleaning up fallen seed pods limits the food source that draws large aggregations. If swarms are already on your home’s exterior, a strong spray of water from a garden hose knocks them off without chemicals. These bugs become more tolerant of pesticides in cool weather when they’re ready to hibernate, making chemical control less effective right when you’d most want it to work.