Promachus yesonicus
This robber fly hunts other insects with a piercing beak but rarely bites people, doing so only if someone catches and handles it directly.
| Where | Grassland and gardens across Japan and Korea |
|---|---|
| Size | 20 to 30 mm body length |
| When | May to August |
This robust robber fly measures 20 to 30 millimetres long and is covered in dense grey-brown bristles, including a thick beard beneath the eyes that protects its face from struggling prey. Males carry a tuft of white hairs at the tip of the abdomen that females lack.
Adults perch in open, sunny spots in grassland, parks, and gardens, darting out to catch flying insects, including bees, beetles, and other flies, with their strong legs. It completes one generation a year, overwinters as a larva, and is active from spring into late summer across Japan and Korea.
Traits
Habitat
Grassland
Colour
Brown, Grey
Active
Day
To people
Mild
Not aggressive toward people and bites only if caught and handled directly, causing a brief, mildly painful puncture.
Activity through the year
Often confused with
Has iridescent green compound eyes, unlike the plain dark eyes of this species, and males lack the white cottony tuft at the tip of the abdomen.
Questions
Is Promachus yesonicus dangerous to people?
Mild. Not aggressive toward people and bites only if caught and handled directly, causing a brief, mildly painful puncture.
When can you see Promachus yesonicus?
Promachus yesonicus can be seen from May to August, by day.
Plate retouched from a photo by Taylor Wichmanowski, CC BY 4.0, iNaturalist Licence
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Last updated 2026-09-27. Every entry is checked against published sources.