Raychis

Guides

What are these tiny flies around my houseplants?

Three different insects get called the same thing, and the fix for each is different. Where the flies sit, and what they do when you disturb the plant, separates them in about ten seconds.

Watch where they come from

Tap the pot and then the leaves. Dark flies that walk over the compost and fly up in a lazy line are fungus gnats, and the answer is in the watering. White flies that lift in a cloud from the undersides of the leaves are whitefly, and the answer is on the plant. Small brown flies hovering near a fruit bowl or a bin belong to the kitchen rather than the plant.

Work down the list

  1. Fungus gnats

    What you would see
    Dark grey-black flies a few millimetres long, running over the compost surface and flying up in a short weak flight when the pot is moved.
    The check
    Push a finger into the compost. Permanently damp compost with organic matter in it is what the larvae live on, and letting the top few centimetres dry out between waterings ends most infestations on its own.
    Fungus gnats

  2. Whitefly

    What you would see
    Tiny white moth-like insects clinging to the undersides of leaves and rising in a cloud when the plant is knocked, with sticky leaves beneath them.
    The check
    Turn a leaf over. Whitefly stay on the plant and never walk on the compost, and the stickiness is what tells them apart from anything harmless.
    Whitefly

  3. Fruit flies from the kitchen

    What you would see
    Small tan or brown flies with red eyes, hovering around fruit bowls, bins, drains and recycling rather than around the plants.
    The check
    Move the fruit bowl for two days. Fruit flies breed on fermenting material and have no interest in compost, and they leave when the food does.

  4. Thrips

    What you would see
    Slender dark specks a millimetre or two long that dart rather than fly, on leaves that are turning silvery and stippled with dark varnish spots.
    The check
    Tap a leaf over a sheet of white paper. Thin dark slivers that run rather than fly are thrips, and the damage to the foliage is what distinguishes them from the harmless flies.
    Thrips

  5. Shore flies

    What you would see
    Stockier dark flies with clear spots on the wings, on the compost of plants that stand permanently wet, often alongside a film of algae.
    The check
    Look at the compost surface for green algal slime. Shore flies feed on that rather than on roots, they harm nothing, and drying the surface out removes them.
    Fungus gnats

  6. Something that came in with the compost

    What you would see
    A short-lived burst of flies from a plant potted on within the last few weeks, tailing off without anything being done.
    The check
    Note the date. An open bag of compost stored damp breeds gnats, and a fresh sealed bag prevents the next round. Store what is left dry and closed.
    Fungus gnats

Still not sure which one it is? Photograph the leaf and compare it against the full library.

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