Small milkweed bug vs Milkweed assassin bug
These two are easy to mix up. Here's how to tell a small milkweed bug from a milkweed assassin bug, and whether either one bites or stings.
Small milkweed bug
Lygaeus kalmii
Milkweed assassin bug
Zelus longipes
≠The key differences
Predatory and more elongate with raptorial front legs; not the red-and-black seed-feeding pattern of Lygaeus kalmii.
⚖︎Side by side
| Small milkweed bug | Milkweed assassin bug | |
|---|---|---|
| To humans | Non-toxic | Painful bite |
| Size | 10-12 mm long | 12-22 mm body length |
| Colours | Orange-red, Black, White (small wing spot), Dark brown (legs/antennae) | Orange, Reddish-brown, Dark brown, Black |
| Family | Lygaeidae | Reduviidae |
| Habitat | Meadows, roadsides, fields and gardens where milkweed (Asclepias) and similar plants grow; sometimes edges of woodlots and disturbed ground. | Open, sunny places with herbaceous plants and shrubs: milkweed patches, gardens, field margins, roadsides and crop edges |
| Range | Widespread across much of North America, from southern Canada through the United States. | Native to the Americas: widespread from the southern United States through Central America into South America. Common in southeastern United States and tropical/subtropical regions. |
| Active | Active from late spring through autumn, peak abundance in summer and early fall; diurnal (active by day). | Warm months (spring to autumn in temperate zones); diurnal and active during daylight |
| Pest? | No | No |
🔍How to spot a small milkweed bug
- Black body with a red-orange X-shaped band across the back and white spots on the black wing membrane.
- Adult length about 10-12 mm; nymphs are wingless and bright orange-red with black markings.
- Found congregating on milkweed seed pods and flowers during summer and fall.
- Smaller and with a white wing-spot compared with the larger Oncopeltus (large milkweed bug).
🔍How to spot a milkweed assassin bug
- Long, slender body 12-22 mm with very long legs, especially the hind legs
- Raptorial forelegs often appear slightly thicker and may show sticky residue used for catching prey
- Orange to reddish-brown coloration with possible darker markings on the abdomen or wings
- Elongated head and a short, three-segmented rostrum (beak) typical of assassin bugs
?Frequently asked questions
What is the difference between a small milkweed bug and a milkweed assassin bug?
Predatory and more elongate with raptorial front legs; not the red-and-black seed-feeding pattern of Lygaeus kalmii.
Is a small milkweed bug or a milkweed assassin bug more dangerous?
Small milkweed bug: Non-toxic. Milkweed assassin bug: Painful bite. Small milkweed bugs do not have a medically important bite or sting. Will bite if mishandled; bite can be painful and may cause localized swelling, redness and itching.
Identification from photos is never certain: don't handle insects you can't identify, and get medical advice for bites, stings or allergic reactions.