Bug FAQCommon Flathorn Plant Bug
Heterotoma planicornis · Order: Hemiptera · Family: Miridae
Also called: Plant bug
Source: Wikipedia
The common flathorn plant bug is a small dark-red or black bug with pale green legs and a flattened second antennal segment. Adults appear from July to September, after eggs laid in young wood overwinter and hatch in May. It feeds on spiders, aphids, mites and also on unripe fruits, buds and nectar of many garden plants, which can harm those plants.
Source: Wikipedia
How to recognize it
They are black or dark red with pale green legs and have short hairs and a distinctive flattened second antennal segment.
Source: Wikipedia
Size
Males are about 4.6 to 5.3 mm long, while females are slightly larger at 4.9 to 5.5 mm.
Source: Wikipedia
Where it lives
They are common in neglected orchards, hedgerows and many gardens.
Source: Wikipedia
What it eats
Both nymphs and adults prey on spiders, aphids and mites. They also feed on unripe fruits, buds, juices and nectar of plants such as hawthorn, alder, hazel, oak, nettles and tansy.
Source: Wikipedia
Life cycle
Eggs are laid in young wood, hatch in May, and the insects become adults by June; there is one generation per year.
Source: Wikipedia
When you see it
Adults are present from July through September, while the eggs overwinter.
Source: Wikipedia
Lookalikes
They look very similar to Heterotoma merioptera and can be hard to tell apart.
Source: Wikipedia
Where it is found in the US
Recorded in 13 of 51 states and DC. Most records: California, Oregon, Washington, New York, Utah, Georgia, Massachusetts, Idaho.
Darker = more records. Counts are museum and citizen-science records, not population size.
Source: GBIF
Status: introduced in Canada; introduced in United States. Source: iNaturalist
Months it is reported in the US
Source: GBIF
More photos
Questions people ask
How can I recognize a common flathorn plant bug?
Look for a small dark-red or black bug with pale green legs, short hairs and a flattened second antennal segment; males are about 4.6 to 5.3 mm and females 4.9 to 5.5 mm long.
Source: Wikipedia
When are these bugs active?
Adults appear from July to September, after eggs laid in young wood hatch in May.
Source: Wikipedia
Same family (Miridae)
North American Tarnished Plant BugLygus lineolarisDamages trees, gardens or crops
Red-spotted Plant BugDeraeocoris ruber
Alfalfa Plant BugAdelphocoris lineolatusDamages trees, gardens or crops
Meadow Plant BugLeptopterna dolabrataDamages trees, gardens or crops
Four-lined Plant BugPoecilocapsus lineatusDamages trees, gardens or crops
Lygus pratensisLygus pratensisDamages trees, gardens or cropsSources
- Wikipedia: https://en.wikipedia.org/wiki/Heterotoma_planicornis
Look it up elsewhere: GBIF · iNaturalist · BugGuide · ITIS · Wikipedia
Text written 2026-10-22 from the sources above and checked sentence by sentence against them. Data fetched 2026-10-22.