Spider mites

What's happening

Spider mites are tiny sap-sucking pests that thrive in the warm, dry indoor air Kentia palms are often kept in. They cluster on the undersides of the leaflets, piercing cells to feed, which leaves the fronds looking dusty, faded, and finely speckled; as the colony grows they spin the delicate webbing you can see strung between leaflets.

How to fix it

Isolate the plant so the mites don't spread. Rinse the whole canopy in a shower or with a hose, paying special attention to the undersides of the fronds, to knock the population down. Then spray thoroughly with neem oil, coating both sides of every frond, and repeat every 5–7 days for three or four rounds to catch newly hatched mites. Raising humidity afterward makes the plant much less inviting to them.

This is general guidance based on common symptoms; individual plants vary.