Symphylans In Cannabis Soil: How To Spot Root Feeders
Quick answer: Symphylans in cannabis soil are slender, white soil animals with many legs that run fast when exposed to light. They are not insects. They feed on roots, sprouting seeds and seedlings, which can stunt plants and leave patches of poor growth. The best way to check for them is a potato bait test on moist soil before planting.
What Are Symphylans?
Garden symphylans, sometimes called garden centipedes, are soil arthropods related to centipedes and millipedes. The UC Statewide IPM Program says they are slender and white, with twelve pairs of legs, fourteen body segments and a pair of antennae, and that they run rapidly when exposed to light.
The Pacific Northwest Insect Management Handbook says garden symphylans measure about 1/4 inch long when mature and have 6 to 12 pairs of legs depending on age. That leg count is what sets them apart from common soil insects, which have only three pairs.
Why Symphylans Matter in Cannabis Beds
Symphylans feed on living plant tissue. UC Cooperative Extension’s Symphylans IPM guide says they feed on living roots, sprouting seeds and fungal hyphae. Feeding damage causes root death, a gnarled look, stunting and greater risk from soil borne disease. UC IPM adds that they may damage seedlings before or after emergence and may slow the growth of larger plants.
Damage tends to be patchy. UC Cooperative Extension says symphylans often occur in hotspots that can range from several square feet to several acres, and the Pacific Northwest handbook notes that hotspots often stay in the same place from year to year.
Where Symphylans Live
UC IPM says symphylans are associated mainly with moist, organically rich soil and feed on decaying as well as living plant material. UC Cooperative Extension says they cause problems in systems with high soil organic matter, crop residue worked into the soil and organic matter that has not broken down. It also notes they are more often found in soils with good structure than in compacted or sandy soils.
They cannot dig tunnels of their own. The Pacific Northwest handbook says symphylans move through cracks, crevices and channels left by roots. They gather in the top 6 inches of soil when it is moist and warm in spring and fall, and move deeper in July and August. In a good habitat they can travel more than 3 feet down.
How to Run a Potato Bait Test
- Pick the time. UC Cooperative Extension recommends bait trapping just before planting in spring.
- Cut the bait. Slice raw potatoes, beets or carrots into thick slices.
- Expose moist soil. Carefully rake away the dry top layer until moist soil shows, without packing the soil pores.
- Scratch the cut face. Scratch the cut surface right before you place it on the moist soil.
- Cover it. Put a cup or a small white pot with no drainage holes over the slice so it does not dry out, and weigh it down with a stone.
- Wait 24 to 36 hours. UC Cooperative Extension says to leave the bait in place for 24 to 36 hours.
- Count fast. Lift the cover and count the symphylans on the soil surface first, because they run and hide quickly, then count the ones on the slice.
- Repeat in several spots. Compare weak patches with healthy areas nearby.
How to read the count: UC Cooperative Extension says that if any symphylans are present on the bait, significant stand loss can occur and taking action is justified. It also says that if you can see them in the soil before planting, they are numerous enough to cause economic damage.
How to Lower Symphylan Numbers in Beds
- Limit fresh organic matter. UC Cooperative Extension advises reducing inputs of undecomposed organic matter. Our guide to composting cannabis garden waste covers how to let material break down first.
- Wait before planting. It recommends waiting to seed or transplant until organic materials have visibly broken down.
- Plant transplants instead of seeds. Transplants give plants more of a head start, according to UC Cooperative Extension. Before you plant cannabis outdoors, check your state’s home grow law.
- Firm the surface after planting. UC Cooperative Extension says mild packing of the soil surface after planting compresses the pore spaces symphylans use to travel. For when firming turns into a problem, see our guide to soil compaction in cannabis beds.
- Weigh tillage carefully. Tillage when symphylans are near the surface can give several weeks of control, UC Cooperative Extension says, but it does not reach deeper symphylans, harms their predators and wears down soil structure over time.
- Replace potting mix in pots. For containers, our own habit is to swap out infested mix rather than try to clean it.
- Consider products only after a bait count. UC Cooperative Extension lists organic insecticides and oil based products among the options. Follow the product label, and check that any pesticide is allowed for cannabis in your state.
Natural Enemies of Symphylans
UC Cooperative Extension suggests promoting predators such as predatory mites, ground beetles, true centipedes and fungi, but notes that biological control alone will likely not be enough. Avoiding constant deep tillage helps keep those predators in the soil.
Troubleshooting
Plants are stunted with stubby roots, but you see no bugs. Symphylans run from light and move deep in midsummer, according to the Pacific Northwest handbook. Run a bait test on moist soil in spring or fall when they are near the surface.
The small soil animals jump. Symphylans do not jump. A jumping critter is more likely a springtail, so see our guide to springtails in cannabis soil.
The many legged bugs are brown and slow. Those are probably millipedes. The Pacific Northwest handbook says millipedes are generally slower moving and have two pairs of legs on each body segment.
Damage returns every season in the same spot. That fits a symphylan hotspot. The Pacific Northwest handbook says hotspots often stay consistent from year to year, and UC Cooperative Extension says tillage does not control symphylans at lower soil depths.
You find round aphids on the roots instead. That is a different pest. Read our guide to root aphids on cannabis.
Sources
- UC Cooperative Extension, Symphylans IPM (December 2023, PDF): https://ucanr.edu/sites/default/files/2024-10/403627.pdf
- UC Statewide IPM Program, Garden Symphylans: https://ipm.ucanr.edu/home-and-landscape/garden-symphylans/
- Pacific Northwest Insect Management Handbook (Oregon State University, Washington State University and University of Idaho Extension), Biology and control of the garden symphylan (revised March 2025): https://pnwhandbooks.org/insect/ipm/garden-symphylan
FAQ
What are symphylans in cannabis soil?
They are small, white soil arthropods related to centipedes, not insects. UC IPM says garden symphylans have twelve pairs of legs, fourteen body segments and a pair of antennae, and run rapidly when exposed to light. In cannabis beds they feed on roots and seedlings, mostly in moist soil rich in organic matter.
Are symphylans harmful to cannabis?
They can be. UC Cooperative Extension says symphylans feed on living roots and sprouting seeds, causing root death, stunting and more risk from soil borne disease. UC IPM says they may damage seedlings and slow the growth of larger plants. Damage is often patchy, showing up in hotspots of weak plants.
How do you test soil for symphylans?
Use a potato bait test before planting. UC Cooperative Extension says to place thick slices of raw potato, beet or carrot on moist soil, scratch the cut face, cover them with a cup and wait 24 to 36 hours. Count the symphylans on the soil first, then on the slice.
How can you tell symphylans from other small soil bugs in a cannabis pot?
Count the legs and watch how they move. Symphylans have up to twelve pairs of legs and run fast from light without jumping. The Pacific Northwest handbook says newly hatched ones can resemble springtails, but springtails jump. Millipedes are slower and have two pairs of legs per body segment.
How do you lower symphylan numbers in cannabis soil?
Start by limiting undecomposed organic matter and waiting until amendments have broken down before planting, as UC Cooperative Extension advises. Use transplants instead of seeds and firm the soil surface after planting. Tillage near the surface gives several weeks of control but harms predators and soil structure.
