Holly leaf miner is a small fly with larvae that cause discoloured blotches by feeding inside holly leaves.

The fly belongs to the family Agromyzidae, there are several hundred known to occur in Britain and many are leaf miners as larvae. More information on Agromyzidae is available from the Agromyzidae recording scheme.

Nearly 900 other insects, including some beetles, sawflies and moths create leaf mines as larvae more information about some of these insects can be found at The leaf and stem mines of British flies and other insects.

Signs that holly leaf miner has been active include:

• Yellowish-white or yellowish-purple blotches occur on the upper surface of older leaves, usually near the centre of the leaf
• In early summer some leaves on holly trees turn yellow and fall from the tree. This is the normal shedding of old leaves and is not caused by the leaf miner

• This insect is part of the biodiversity hollies support and should be tolerated, it has little impact on the health and vigour of a holly
• Most leaf mining species will have natural enemies including parasitoid wasps; parasitic wasps can lay eggs in the larvae even through the leaf. The wasp’s young then eat the larvae, so it never turns into an adult. Birds such as blue tits can use their sharp beaks to peck through the leaf and get at the fly larvae inside
• On small specimen plants it is feasible to remove mined leaves, but not if this would result in significant defoliation 

Grubs of the holly leaf miner tunnel inside the leaves. There is one generation a year, and the adult flies lay eggs on the new foliage in May to June. When the larvae have completed their feeding, in the following spring, they pupate inside the leaf mines.