Several common beetle species wear red and black coloring, and the one you spotted depends on where you found it, how big it is, and what it was doing. The most likely candidates are lady beetles, red lily beetles, red turnip beetles, and blister beetles. A few red and black insects that look like beetles are actually true bugs, not beetles at all. Here’s how to tell them apart and what to do about each one.
Lady Beetles (Ladybugs)
The most familiar red and black beetle is the lady beetle, commonly called a ladybug. The seven-spotted lady beetle has a hard, shiny body about 1/3 inch long and 1/6 inch wide. Its wing covers are orange or reddish with seven black spots, and the head and thorax are black with two white blotches on each side. Many other lady beetle species share a similar color scheme, and telling them apart with certainty can be surprisingly difficult since dozens of species look nearly identical.
Lady beetles are beneficial predators. They eat soft-bodied insects including aphids, mealybugs, whiteflies, and psyllids. Young larvae pierce and suck the contents from prey, while older larvae and adults chew and consume entire insects. The larvae look nothing like the adults. They resemble tiny alligators, blackish or dark gray with orange or yellowish spots, growing up to 1/3 inch long. If you find lady beetles in your garden, they’re helping you.
Red Lily Beetle
If you found a bright red beetle on your lilies, it’s almost certainly the red lily beetle (Lilioceris lilii). These striking beetles are about 1/4 to 1/3 inch long with a completely bright red body and a black head and legs. They belong to the leaf beetle family, many members of which are brightly colored and metallic.
Red lily beetles attack true lilies (Lilium species) and fritillaries. They can also damage lily of the valley and Solomon’s seal, though less severely. They leave daylilies, canna lilies, and calla lilies alone, so if your plant is one of those, you’re dealing with something else.
The larvae are especially unpleasant. They’re plump, slug-like, orange or yellowish with black heads, reaching almost 1/2 inch long at maturity. As a defense strategy, they cover themselves in their own excrement, making them look like slimy greenish-brown slugs or small piles of animal droppings. It’s effective camouflage, but it means you might not recognize them as beetle larvae at first glance.
There’s one generation per year, but adults can live several years. They overwinter in soil and plant debris, not necessarily near lilies, then emerge in spring to feed, mate, and lay eggs. A single female lays between 250 and 450 eggs. Those eggs hatch in four to eight days, and larvae feed for two to three weeks before dropping into soil to pupate. New adults emerge 16 to 22 days later and continue feeding through fall. Because they’re strong fliers, they can travel long distances to find host plants.
Managing Red Lily Beetles
For a small number of lilies, hand-picking works. Crush adults and larvae by hand, or knock them into a container of soapy water. Crush any eggs you spot. Repeat regularly throughout the growing season. If infestations become chronic, organic insecticides containing azadirachtin, pyrethrins, or spinosad are effective, as are horticultural oils and insecticidal soap. For severe, recurring problems, replacing lilies with non-host plants may be the most practical solution.
Red Turnip Beetle
The red turnip beetle is red with black stripes running down its wing covers. It feeds on plants in the mustard family: turnip, radish, canola, rapeseed, and mustard, along with other cruciferous plants. It’s more common in areas with sandy soils.
Damage from red turnip beetles ranges from minor leaf loss to total defoliation and plant death. The beetle feeds on leaves, flowers, stems, and seedpods. Infestations typically start at field edges and spread inward, often originating from weedy areas or volunteer mustard-family plants that weren’t cleared in fall or spring. For home gardeners growing brassicas, controlling cruciferous weeds nearby and removing volunteer plants reduces the chance of these beetles moving into your crops.
Blister Beetles
Some blister beetle species are red and black, and these are the ones you genuinely need to be careful around. Blister beetles secrete a fluid containing cantharidin, a potent blistering agent that causes skin irritation on contact. Several species in North America look similar, with red or orange-and-black coloring.
If a blister beetle lands on you, do not slap or crush it. Crushing releases the defensive fluid onto your skin. Instead, gently blow it away or remove any clothing it has landed on, then wash the exposed area with soap and water. If you do get fluid on your skin, rinse with water immediately. There’s no antidote for cantharidin. Treatment focuses on managing symptoms: corticosteroids to reduce inflammation and antibiotics if open blisters become infected. A tetanus vaccine update is also recommended if you’re not current.
Cantharidin is toxic to all mammals. It poses a particular danger to horses. Three-striped blister beetles can contain 1 to 12 percent cantharidin by dry weight. Even species with lower concentrations, like oil beetles in the genus Meloe, carry enough that a few hundred beetles could be lethal to a 1,000-pound horse if consumed in hay. If you keep horses and notice blister beetles in your hay fields, that’s a serious concern worth addressing before baling.
Red and Black Insects That Aren’t Beetles
Several red and black insects commonly get mistaken for beetles but are actually true bugs, a completely different group. The easiest way to tell them apart: true bugs have piercing, straw-like mouthparts for sucking plant sap, while beetles have chewing mouthparts. True bugs also fold their wings flat over their backs in an overlapping “X” pattern, whereas beetle wings meet in a straight line down the middle.
The most common lookalikes are boxelder bugs, small milkweed bugs, and firebugs. All of these feed by sucking sap from plants rather than chewing leaves. Their red and black coloring is a warning signal to predators, advertising chemical defenses. Milkweed bugs, for instance, store heart-affecting toxins they absorb from milkweed seeds. Boxelder bugs release foul-smelling, disgusting-tasting liquid from abdominal glands when threatened. This warning coloration pattern is so effective that multiple unrelated species on milkweed plants, including beetles, bugs, butterflies, and moths, have independently evolved orange-and-black markings.
Keeping Red and Black Insects Out of Your Home
If red and black insects are getting inside your house, you’re most likely dealing with boxelder bugs or a similar overwintering species rather than a true beetle. These insects are attracted to buildings with significant southern or western sun exposure, and they’re most numerous after hot, dry summers. As temperatures drop in fall, they push into cracks and gaps around the building to find shelter, then often end up near windows indoors.
Prevention is the most effective strategy, and the work needs to happen before the end of August, before they start seeking shelter. Seal cracks and gaps where cables, pipes, faucets, dryer vents, and wires enter the building. Repair or replace damaged window and door screens, including screens on roof vents, soffit vents, and bathroom fans. Install door sweeps on all exterior doors and a rubber seal along the bottom of garage doors. For brick, stone, or stucco buildings, seal any exterior cracks 1/8 inch or larger with silicone or elastomeric caulk, but don’t seal weep holes in brick veneer. Instead, insert ventilation plugs from a hardware store.
Once they’re inside, there’s no need for pesticides. Vacuum them up or sweep them into a dustpan. They don’t bite, don’t breed indoors, and don’t damage your home. They’re just looking for a warm place to wait out winter.