Are Citronella Ants Harmful To Garden Plants Or Beneficial?

Quick answer

Citronella ants are generally not directly destructive to healthy garden plants, but they can be indirectly harmful. They rarely chew foliage or feed on roots, yet they tend honeydew-producing insects (aphids, scales, mealybugs) and can protect those pests from predators. Their nesting and tunneling can also disturb seedlings and potted plants. At the same time, they provide some ecosystem services such as soil aeration, nutrient recycling, and predation on certain small pests. Whether they are a problem depends on scale, the presence of other pests, and your tolerance for ant activity in garden beds.

What are citronella ants?

Citronella ants is a common name used for small, yellowish-brown ants that emit a citrus or citronella-like scent when crushed. In North America the name usually refers to species in the Lasius group (for example Lasius interjectus) that nest underground and are most active in spring and early summer.

Typical characteristics:

Small workers, often about 2.5 to 4 mm long.
Yellow to light brown coloration.
Nesting habits: colonies are generally subterranean, under stones, in soil, in planters, and sometimes under mulch.

Distinctive smell when crushed, like lemon or citronella oil.

Understanding these traits helps separate citronella ants from other common garden ants (e.g., pavement ants, Argentine ants) so you can choose the right management approach.

Direct impacts on plants

Citronella ants do not typically feed on living plant tissue the way caterpillars or voles do. Direct impacts are limited, though a few situations can be problematic:

Seedling disturbance: tunneling and nest-building near newly sown seeds or delicate seedlings can expose roots or displace soil, reducing germination and establishment.

Root exposure in containers: nests in pots or raised beds may disturb roots and reduce moisture retention around roots.
Increased soil aeration: this is usually a neutral or beneficial effect, but in very sandy soils it can dry out planting media faster.

Overall, direct plant damage from citronella ants is uncommon and usually minor unless colonies are very large or concentrated in containers and seed flats.

Indirect impacts, why gardeners worry

The principal reason citronella ants become a garden pest is their mutualistic relationship with honeydew-producing insects. They do not eat the plant-sap pests, they “farm” them for honeydew, a sugary excretion, and in return protect the pests from predators and parasitoids.

Key indirect impacts:

Aphid protection: ants move aphids to new feeding sites, shelter them, and fend off lady beetles, lacewings, and parasitic wasps, allowing aphid populations to grow unchecked.

Scale and mealybug protection: similar protective behavior can increase infestation severity on woody plants, ornamentals, fruit trees, and houseplants.
Root aphids: some ants tend root-feeding aphids that live in potting media or soil, causing wilting and poor growth that looks like nutrient or water stress.

When ants are abundant and honeydew producers are present, the result for plants can be significant: decreased vigor, stunted growth, sooty mold development on leaves from honeydew, and reduced fruit quality.

Possible benefits of citronella ants in the garden

While often blamed, ants contribute several positive functions in garden ecosystems:

Soil aeration and mixing: their tunneling increases porosity and helps water infiltration.
Organic matter breakdown: ants move and fragment organic material, speeding decomposition and nutrient cycling.
Predation: citronella ants and other ants consume a range of small arthropods and insect eggs, reducing some pest populations.

Seed dispersal: many plants rely on ants to move and bury seeds (myrmecochory), aiding germination and plant spread for some native species.

These benefits are real but typically less visible than the damage caused when ants protect sap-sucking pests.

How to decide whether to control them

Control is only necessary when ants are causing a clear problem. Consider these questions:

Are you seeing heavy aphid, scale, or mealybug infestations on plants that ants are protecting?

Are seedlings, potted plants, or root systems being disturbed by tunneling?
Is the presence of ants creating sooty mold or reduced vigor that affects crop yields or aesthetics?

If the answer to one or more of these is yes, management is justified. If ants are merely present but not associated with plant-damaging pests or significant disturbance, tolerating them is often the best approach.

Identifying whether ants are the problem

Steps to diagnose the situation:

Observe the ants’ behavior. Do they cluster on stems, leaves, or roots where honeydew producers are present?
Check undersides of leaves and new growth for aphids, scales, or mealybugs. Look for sticky honeydew and sooty mold.
Gently disturb soil around the base of affected plants. Are there tunnels, nest entrances, or active workers moving in and out?

Do a simple smell test: gently squash a worker on a paper towel away from plants to check for the citronella scent (use gloves if you prefer).

These observations will tell you whether ants are a symptom (they’re farming pests) or a primary cause (nesting that disrupts plant roots).

Practical, least-toxic management options

When control is needed, use an integrated approach that focuses on the pest ants’ food source and the ants themselves, while minimizing harm to beneficial insects.

Non-chemical and cultural tactics:

Remove honeydew producers: wash aphids off with a strong spray of water, prune heavily infested shoots, and use insecticidal soaps or horticultural oils targeted at the sap-suckers, not the ants.
Encourage natural enemies: lady beetles, lacewings, syrphid flies, and parasitic wasps reduce aphid populations when ants are not protecting them.

Reduce nesting sites: minimize excessive mulch depth, avoid dense groundcovers near trunks, and remove stones or debris that favor subterranean nests.
Physical barriers: apply sticky bands around tree trunks to prevent ants from accessing canopy pests (replace bands regularly to avoid trapping beneficials).
Isolate potted plants: place ant-repellent barriers like moats or elevated stands; replace heavily infested potting soil when root aphids are present.

Targeted baiting strategies:

Use slow-acting ant baits formulated for the foraging preference of the species. For sugar-loving ants, use sweet baits; for protein-preferring ants, use protein-based baits. Citronella ants often accept sugary baits because of their honeydew association.

Place baits along ant trails and at nest entrances rather than broadcasting insecticide. Bait workers will carry bait back to the colony, suppressing the nest more effectively.
Follow label instructions on commercial baits. Many contain borax or boric acid and are low-risk when used as directed, but keep them away from pets and children.

Least-recommended methods:

Broad-spectrum contact insecticides: these kill beneficial predators and can make aphid problems worse by removing natural enemies.
Spraying nests with insecticide without baiting: temporarily reduces worker numbers but often results in quick recovery.

When to call a professional

Consider professional pest control if:

Ants are protecting serious infestations of pests on valuable fruit trees or ornamentals and on-site treatments have failed.

Colonies are large, widespread, and causing structural or repeated plant damage.

A good pro will identify the species, target baits appropriately, and use mound treatments or soil injections in a way that minimizes impact on non-target organisms.

Practical takeaways for gardeners

Identify first: confirm the ants are citronella ants and determine whether they are farming aphids or nesting in pots before acting.
Focus on the source: control honeydew-producing pests to remove the attractant for ants.
Use baits, not sprays: targeted baits applied on trails and at nest entrances are more effective and less disruptive than broad insecticide sprays.

Protect seedlings and containers: avoid heavy ant nesting in pots and seed flats; repot and replace heavily infested media.
Preserve natural enemies: encourage and protect predator insects by avoiding blanket pesticide use.
Monitor: ant populations may fluctuate year to year; intervene only when plant health or production is clearly affected.

Conclusion

Citronella ants are not inherently plant killers, but their behavior can lead to serious plant problems indirectly. The key is to decide based on evidence: if ants are simply present, they may be tolerated and even beneficial; if they are protecting aphids or nesting in ways that harm seedlings or potted plants, take targeted, least-toxic measures to reduce their impact. Using identification, cultural controls, natural enemies, and targeted baits will resolve most issues while preserving beneficial functions ants provide in the garden.