# Do sticky traps work?

> Sticky traps work as a monitoring tool, not a cure. Yellow cards catch fungus gnats, whiteflies, winged aphids and leafminers; blue cards are somewhat more attractive to thrips. They catch only flying adults, so they never fix larvae in the medium or spider mites. Count catches weekly and replace the card: a rising count is your early warning, and a falling count shows the real treatment is working.

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- Topic: Pests · Type: How-to
- Evidence: Established · Status: Draft: awaiting expert review
- Full article: [Fungus gnats: the watering problem with wings](https://genetixbay.com/knowledge/pests/fungus-gnats.md)
- Also asked as: Do yellow sticky traps work? | Blue sticky traps for thrips | Will sticky traps get rid of fungus gnats? | Where should I put sticky traps in my tent? | Yellow or blue sticky cards?
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Short answer

[Sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md) work well for what they are: a counter of flying adult pests. Yellow cards catch [fungus gnats](https://genetixbay.com/knowledge/glossary/fungus-gnat.md), [whiteflies](https://genetixbay.com/knowledge/glossary/whitefly.md), [winged aphids](https://genetixbay.com/knowledge/glossary/alate.md) and [leafminers](https://genetixbay.com/knowledge/glossary/leafminer.md); blue cards pull somewhat more [thrips](https://genetixbay.com/knowledge/glossary/thrips.md). Counted weekly they give early warning, but they rarely control a pest by themselves. *Established* as a monitoring method.

## Why

Insects fly to the colour. Many small flying pests are drawn to yellow, and thrips are drawn to blue and yellow [1][2].

Only adults are caught. Fungus gnat larvae live and feed in the top few centimetres of wet medium, so cards do nothing about the stage that chews roots [3]. Control comes from drier media plus Bti, [nematodes](https://genetixbay.com/knowledge/glossary/steinernema-feltiae.md) or [soil predatory mites](https://genetixbay.com/knowledge/glossary/stratiolaelaps-scimitus.md) [4].

Wingless pests are invisible to cards. [Spider mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) are found with a lens on leaf undersides, not on cards [5].

Trends beat totals. A count that climbs week on week is the signal to act; a count that falls over 2–3 weeks confirms a treatment is working [3].

## The numbers

| Pest | Card colour | Placement |
|---|---|---|
| Fungus gnats | Yellow | Flat on or just above the medium |
| Whiteflies, winged aphids, leafminers | Yellow | Just above the canopy, several per room |
| Thrips | Blue or yellow | Just above the canopy |
| Spider, broad and [russet mites](https://genetixbay.com/knowledge/glossary/hemp-russet-mite.md) | Not caught | Use a 10–20x lens |
| Counting | Weekly | Count by type, record, replace |

## What to do

1. Hang one or two cards per small tent, more in rooms, from day one.
2. Put gnat cards low and foliar-pest cards just above the canopy.
3. Count weekly by pest type and write it down.
4. When counts rise, identify the pest and treat the cause: watering for gnats, predators for thrips.
5. Remove or reduce cards while releasing flying [beneficials](https://genetixbay.com/knowledge/glossary/biological-control.md), which they also catch.

## Common mistakes

- Expecting cards to clear an infestation.
- Leaving the same card up for months, so nobody knows what is new.
- Looking for spider mites on cards.
- Letting cards touch buds or hair.

## Related

- Full article: [Fungus gnats: the watering problem with wings](https://genetixbay.com/knowledge/pests/fungus-gnats.md)
- Answers: [Preventing pests indoors](https://genetixbay.com/knowledge/answers/how-to-prevent-pests-indoors.md) · [Small white bugs in soil](https://genetixbay.com/knowledge/answers/small-white-bugs-in-soil.md)
- Articles: [Thrips](https://genetixbay.com/knowledge/pests/thrips.md) · [Whiteflies](https://genetixbay.com/knowledge/pests/whiteflies.md)
- Terms: [sticky trap](https://genetixbay.com/knowledge/glossary/sticky-trap.md) · [Bti](https://genetixbay.com/knowledge/glossary/bti.md)

## Follow-up questions

**Will sticky traps get rid of fungus gnats?** Sticky traps will not get rid of fungus gnats on their own, because they catch only flying adults while the larvae keep feeding in the wet medium. Fix the watering first by letting the top 2–5 cm (1–2 in) of soil dry, then use Bti, Steinernema feltiae nematodes or soil predatory mites against larvae. Use yellow cards to count adults weekly and confirm numbers are falling.

**Do sticky traps catch spider mites?** Sticky traps do not catch spider mites usefully, because spider mites are wingless and walk or drift between plants rather than fly to coloured cards. Find them with a 10–20x lens on leaf undersides, looking for oval mites about 0.5 mm long, round clear eggs and pale stippling on the upper leaf surface. A branch tapped over white paper also shows moving specks.

**Where should I put sticky traps?** Place sticky traps for fungus gnats flat on or just above the surface of the medium, and traps for thrips, whiteflies and winged aphids just above the canopy, away from buds and hair. Use several in a room, because whiteflies do not fly far. Mark a counting area, count catches by type every week, write the number down and replace the card.

## Sources

1. Michigan State University Extension. Managing greenhouse insects. https://www.canr.msu.edu/news/managing_greenhouse_insects
2. UC IPM. Pest Notes: Thrips (Publication 7429). https://ipm.ucanr.edu/PMG/PESTNOTES/pn7429.html
3. UC IPM. Pest Notes: Fungus Gnats (Publication 7448). https://ipm.ucanr.edu/legacy_assets/pdf/pestnotes/pnfungusgnats.pdf
4. UConn IPM. Biological Control of Fungus Gnats. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-fungus-gnats/
5. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html