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Hawthorn fly

Hawthorn flies are actually mosquitoes and belong to the family of March flies.

Also known as:
St. Mark’s fly

Do not confuse with:
Dark-winged fungus gnat (Sciara analis)

recognize hawthorn fly
Bibio marci, photo: © entomart

Hawthorn fly (Bibio marci). Hawthorn flies are actually mosquitoes and belong to the family of March flies (Bibionidae). Hawthorn flies are found all over the world and have 12 genera and over 600 species.
Hawthorn flies are between 4 and 9 mm in size, are black and, unlike many other insects, have “thick” legs. In spring, they appear in large numbers.
The female fly lays her eggs in a clump in grassland, preferably near manure. The legless larvae resemble leatherjackets but have a black head – that of leatherjackets is brown.
The larvae live on dead plant parts and manure residues, later on grass. The damage to the turf only becomes visible in the fall.
Birds (starlings and gulls) are among the natural enemies of hawthorn fly larvae.

Where to find

  • Common in lawns and grasslands

Control

Difficult to control; any damage to the lawn is not visible until autumn. The hawthorn fly larvae have long since become adult flies by then.

Prevention

Provide a bird-friendly environment: birds (gulls, starlings) eat the larvae. Occasionally releasing a flock of chickens onto the grass also helps.

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