Why does my calathea have fine webbing between the leaves?

On a calathea this is a fine, silvery web between a leaf and its stalk or along the underside of the leaf, with a pale stippling or speckling on the upper surface where the mites have fed. The leaves look dull.

The most likely cause is spider mites, as the entry says, and they take hold quickly on a plant kept too dry. The Royal Horticultural Society names red spider mites as a pest of calatheas, with speckled, yellowing or silvery leaves and fine webbing. Mites breed fast in warm, dry air and slowly in damp air, and a heated room in winter, where the air is far drier than this plant wants, is where they do best.

To confirm it in a minute, hold a sheet of white paper under a leaf and tap it. Spider mites fall as specks the size of a full stop and then walk, which dust does not do. Turn a leaf over and look along the veins on the underside, and at the place where the leaf stalk joins the clump. Check the room too: webbing that began within weeks of the heating coming on, on a plant that was clean before, is the likelier story.

Two other causes are worth ruling out. A new plant bought or given in the last month may have brought the mites in. And other sap suckers leave different signs: the RHS says mealybugs or soft scale leave black, powdery sooty mould that follows the sticky residue they excrete, where mites leave only a web.

Speckled leaves stay speckled, so judge the recovery by the webbing and by new leaves. Mites run through a generation quickly, and it takes several weeks of repeated washing before new webbing stops appearing. After that, new leaves should open clean, which in the growing season is a matter of weeks.

What this plant wants

The fix

Rinse both sides of every leaf, raise the humidity, and treat weekly with an insecticidal soap until no new webbing appears.

Read on

Fine webbing between the leaves

The same sign on any plant, with the causes in the order they are likely.

Calathea care

Light, water, feeding, repotting and the rest of the entry.

Check it in the diagnoser

Opens with the plant, the part and the sign already chosen.