Milkweed beetles are a genus of longhorned beetles that specialize in eating milkweed plants. The larvae bore into the roots and overwinter below ground; the adults emerge in late spring and chew the foliage and leaves of milkweeds.
The adults are red with black spots or other markings. The bright red is a warning: Like other insects that eat milkweeds, these beetles ingest milkweed’s toxic chemicals and become unpalatable or sickening to predators.
The genus name, Tetraopes, means “four-eyed,” and beetles in this genus are sometimes called “four-eyed beetles.” Each eye is divided by an antenna base, making it look like two.
The species are very similar. At least three species are common in the eastern United States; several more are found farther west. The different species' ranges match those of their favorite milkweed host species.
- Red-femured milkweed borer (T. femoratus): antennae have white rings (antennae are not all black), the legs are partially reddish (not all black), and it has relatively small black spots. A variable and widespread species that eats several types of milkweeds.
- Red milkweed beetle (T. tetrophthalmus): antennae are all black (without white rings), the legs are all black (not partially reddish), and it has relatively large black spots. The middle black spot on each elytrum (shell-like wing cover) is elongated. This species specializes on eating common milkweed (A. syriaca) and sometimes other milkweeds or dogbanes.
- Blackened milkweed beetle (T. melanurus) has heavy black markings on the hind part of the wing covers, which look like a pair of heart-shapes or a heart on top of a triangle. There are black spots on the pronotum, and the antennae are all black. It feeds mostly on butterfly weed (A. tuberosa) and apparently also common milkweed (A. syriaca).
Learn more about these and other longhorned beetles on their family page.