Appearance & Identification
The grass fly (Thaumatomyia notata) belongs to the family Chloropidae and is very small, measuring about 2 to 3 millimeters in body length.
It has a yellowish shiny body with usually three black longitudinal stripes on its back. Its eyes shimmer greenish – a typical feature of living animals.
The grass fly is often mistaken for fruit flies, but unlike them, it is not interested in food or kitchen waste, but seeks light, warmth, and sheltered places.
Lifestyle & Habitat
Originally, grass flies live on grasses, fields, and meadows, where they feed on plant sap or hunt small insects.
In late summer and autumn, many animals move towards buildings to overwinter there.
They find their way through small cracks or crevices in windows, joints, or roof areas and rest there until spring.
At mild temperatures, they can also remain active in winter and then occasionally appear in living spaces – especially on windows, light-colored walls, or lamps.
Are grass flies dangerous?
No – grass flies are not considered hygiene pests.
They do not bite or sting, do not transmit diseases, and usually do not reproduce indoors.
Nevertheless, they can be perceived as annoying, especially when they appear in larger numbers or gather on window panes.
Prevention against grass flies
Since grass flies like to enter houses in autumn, a few simple measures help keep them away:
- Seal windows and doors – close small gaps or cracks.
- Install insect screens – especially on skylights or transom windows.
- Keep windowsills clean – regularly remove dead flies.
- Reduce light sources in the evening – grass flies are strongly attracted to light.
- Remove dust and plant debris – they often serve as resting places.
Chemical control is not necessary – simple prevention is usually enough to keep the animals away.
Conclusion
The grass fly is a natural part of our environment – harmless but sometimes annoying.
Its appearance in autumn is a seasonal phenomenon that can be easily controlled with a little attention and proper sealing.
