Thrips on houseplants: how to spot them and get rid of them

Thrips are tiny, slender insects, about 1/20–1/16 inch long, that scrape and suck the contents of leaf cells and leave silvery streaks and black specks behind. Getting rid of them takes repeated treatment: rinse the plant, then spray insecticidal soap, horticultural oil or spinosad every 5–7 days for 4–6 weeks, because eggs hidden inside leaves and pupae in the soil survive any single spray.

Thrips have become one of the most common pests in collector aroid collections, and they spread easily between monstera, philodendron, pothos, anthurium, ficus and hoya. Here's how to confirm them and break the cycle.

How to identify thrips

University of Minnesota Extension describes thrips as 1/16-inch, slender, cylindrical insects with slender wings folded over their backs, yellowish to brownish to black, active indoors at any time of year. UC IPM puts most species at less than 1/20 inch and notes their fringed wings.

• Larvae: pale yellow, cream or whitish, wingless, slow, often along veins on leaf undersides.
• Adults: tan, brown or black, sometimes banded; quick, and they jump or fly when disturbed.
• Look-alikes: spider mites are rounder, eight-legged and spin webbing; aphids are pear-shaped and leave sticky honeydew; whiteflies are white and moth-like; fungus gnats fly around the soil surface and don't feed on leaves (see our sister site's fungus gnat guide).

Paper test: hold a sheet of white paper under a leafy stem and tap the stem firmly. Thrips fall and show up as tiny moving slivers. A 10x hand lens confirms the fringed wings and slender shape.

Signs of thrips damage

• Silvery, bronze or pale streaks and patches where emptied cells fill with air; UC IPM describes scabby, silvery to dark brown discoloration.
• Tiny black specks of excrement scattered over the damaged areas.
• Distorted new growth: twisted, scarred or stunted new leaves; on aroids, new leaves may emerge already scarred.
• Flower damage: streaked petals and buds that brown or fail to open.
• Gradual loss of vigor in heavy infestations; UMN notes infested plants can be damaged and their vigor reduced.

Some thrips species can also bite people, causing a brief itchy prick. And in greenhouses, western flower thrips spread plant viruses such as impatiens necrotic spot virus; at home, discard plants with ringspots or unusual bronze patterns that don't respond to treatment.

Why thrips are hard to get rid of

UC IPM lays out the life cycle: egg, two larval stages, prepupa, pupa and adult, completed in as little as 2 weeks in warm conditions. Females insert eggs inside leaf tissue, where sprays can't reach. Many species then drop to the soil or leaf litter to pupate. A single spray kills only the larvae and adults present that day, and a new generation emerges a week later. That's why treatment must overlap at least two to three full cycles.

How to get rid of thrips: a 6-week plan

Week 1: isolate and knock down

1. Isolate the plant in another room. Check every plant nearby, especially those whose leaves touched it.
2. Prune the worst-damaged leaves and spent flowers and bag them.
3. Rinse the plant thoroughly in the shower with lukewarm water, both leaf sides and stems, while covering the soil with a plastic bag.
4. Scrape off the top inch of potting mix and replace it to remove some pupae.
5. Spray the entire plant, upper and lower leaf surfaces, stems and leaf joints, until dripping, with one of:
   • Insecticidal soap (potassium salts of fatty acids).
   • Horticultural oil or neem oil; see neem oil for mixing and leaf-safety tips.
   • Spinosad, a bacterial-derived insecticide that UC IPM lists among options for stubborn thrips; check that the product is labeled for indoor plants.

Always follow the label, test on one leaf first, and spray out of direct sun.

Weeks 2–6: repeat every 5–7 days

6. Repeat sprays every 5–7 days for at least 4–6 weeks. Rotate products (soap one week, spinosad the next) to reduce the chance of resistance.
7. Hang blue or yellow sticky cards at plant height to catch flying adults and to monitor numbers.
8. Re-inspect weekly with the paper test. Keep treating for two more weeks after the last thrips is seen.

Remember UC IPM's point: damaged tissue won't recover. Judge success by clean new leaves, not by the old scarred ones.

Severe or recurring infestations

For large collections, a soil-applied systemic insecticide labeled for houseplants is a last resort; see systemic insecticides for products, safety and limits. Systemics are not for edible plants, and keep them away from pets and children.

Some collectors use predatory mites (Amblyseius cucumeris or A. swirskii) sold online; they work best in warm, humid conditions and as prevention or alongside soap, not with oils or broad-spectrum sprays.

Treatment options compared

Preventing thrips

• Quarantine new plants for 2–4 weeks and do the paper test before adding them to your collection.
• Keep cut flowers away from houseplants; bouquets are a common source.
• Inspect plants brought in from outdoors before fall.
• Keep sticky cards near collections as an early warning.
• Wipe leaves monthly and check new growth whenever you water.
• Thrips, like spider mites, favor warm, dry indoor air; keeping humidity at 40–50% helps plants cope.

For the full lineup of indoor pests and how to tell them apart, see common houseplant pests.