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Red Milkweed Beetle

Tetraopes tetrophthalmus (other milkweed longhorns: Tetraopes spp.)[3]

The red milkweed beetle is a red-orange longhorned beetle with black spots and long black antennae that lives and feeds only on milkweed; its larvae develop on milkweed roots and stems.[1][2]

Group
Insect
Order
Coleoptera
Family
Cerambycidae
US records
30 states
Sources
3 cited
Updated
2026-10-16
Red milkweed beetle, red with black spots and long black antennae, on a milkweed leaf
Red milkweed beetle, red with black spots and long black antennae, on a milkweed leaf. (c) Katja Schulz, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0
On this page
  1. Identification
  2. Look-alikes
  3. Where it lives
  4. Biology
  5. Damage and signs
  6. Health risk
  7. Control
  8. Related profiles
  9. Common questions
  10. Sources

How to identify it

  • Milkweed longhorns are reddish to red-orange with black spots and about 10-16 mm long; the red milkweed beetle is darker red than its western relatives.[1]
  • Their bright colors warn predators that they taste bitter from the cardiac glycosides in milkweed.[2]

Look-alikes

Look-alikeHow to tell them apart
Other milkweed longhornsSeveral other Tetraopes species occur in the West; patterns vary a lot, and one small species is only 7-9 mm.[1]

Where it lives

It is the most common milkweed longhorn in the eastern United States and reaches into eastern Colorado.[1]

US map: public records from 30 states since 1990 (GBIF).

Biology and life cycle

Females lay eggs near the base of milkweed plants, often at the root crown; larvae tunnel into soil or shallowly into stems.[1][2]

Adults spend nearly all their time on milkweed, feeding, resting and mating, and typically live about a month.[1]

Damage and signs

  • Adults chew milkweed leaves, buds and flowers; larvae feed on roots and stems.[1][2]
  • Kentucky Extension traced poor growth of a gardener's swamp milkweed to this beetle's feeding.[2]

Health risk

None to people or pets.[1]

Control

Prevention

Usually tolerated: it is a native milkweed specialist, and populations rise and fall from year to year.[1][2]

Common questions

What are the red beetles with black spots on my milkweed?
Likely red milkweed beetles, longhorned beetles that feed only on milkweed.[1][2]
Should I spray them?
Usually not; they are native milkweed specialists whose numbers rise and fall from year to year.[1][2]
Why are they so brightly colored?
The colors warn predators that they taste bitter from milkweed toxins.[2]

Sources

  1. Colorado State University Extension (Colorado Insects of Interest, W. Cranshaw), “Milkweed Longhorns (Colorado Insects of Interest).” wci.extension.colostate.edu/wp-content/uploads/sites/14/2017/03/Milkweed.longhorns.pdf (accessed 2026-10-15)
  2. University of Kentucky Cooperative Extension, Franklin County, “Milkweed Beetles.” franklin.ca.uky.edu/milkweed-beetles (accessed 2026-10-15)
  3. iNaturalist, “Tetraopes tetrophthalmus taxon page (order and family).” www.inaturalist.org/taxa/118559 (accessed 2026-10-06)

Updated 2026-10-16. Built from sourced records. Spot an error? Tell us.