Do Ants Eat Scale Insects? Understanding the Ant-Scale Relationship and How to Control It

What Happens Between Ants and Scale Insects

Ants do not simply eat scale insects—they typically protect and “farm” them instead.
Many ant species exhibit a symbiotic behavior where they attend honeydew-producing sap-feeding insects such as scale insects and mealybugs. In this relationship, the scale insects feed on plant sap and excrete a sugary liquid called honeydew; ants harvest this honeydew and, in return, protect the scale insects from predators, move them to better feeding spots, or transport them to sheltered areas.
This mutualism benefits ants (a reliable carbohydrate source) and benefits scale insects (reduced predation and better placement), but it brings problems for plant health because the scale population is boosted and protected.

Why This Ant-Scale Relationship Matters for Plant Health

Because ants protect scale insects, the damage to plants can escalate more quickly than if the scales were unmanaged.
When ants attend scale insects:

• The scale population may become denser because natural enemies (parasitic wasps, predatory beetles) are excluded or driven off.
  

• Honeydew accumulates, leading to black sooty mold on leaves and stems, reducing photosynthesis and aesthetic value.

• Ant trails plus scale patches often indicate infestation hotspots—true that seeing ants on a trunk or branch often signals scale insect presence.

• Because the protective “shield” provided by ants slows natural control, conventional treatments may be less effective unless ant activity is addressed.
  Thus, plant health programs must consider both the scale insect and its attending ant population for effective management.

Can Ants Actually Eat Scale Insects?

In typical horticultural and agricultural settings, ants are not major predators of scale insects—they do not regularly consume them as food.
While some ecological studies report instances where certain ant species will prey upon sap-feeding insects under specific conditions, the predominant behavior with scale insects is one of tending rather than eating. For example, research shows that in ant-excluded plots, scale insect mortality (due to predators or fungus) is higher, indicating that ants reduce predation rather than act as predators.
In summary: yes, ants may occasionally prey on scale insects in rare cases, but the usual ant behavior is to protect them rather than eat them. For practitioners, assuming ants will “clean up” scale insects is a mistake.

What to Look For: Signs of an Ant-Scale Partnership

If you suspect that scale insects are being protected by ants (making control more difficult), watch for these indicators:

• Sticky residue (honeydew) on leaves, stems or under infested plants.

• Presence of black or dark film of sooty mold over foliage, often located where honeydew collects.

• Visible scale insect bodies (small domes, bumps, shells) on stems, petioles or leaf undersides.

• Ant trails or ant activity leading up trunks, along branches or within the canopy.

• Rapid spread of scale insects or recurring infestations despite treatments—this often indicates ant attendance is supporting the pest.
  Identifying this partnership is critical because control must break the ant-scale cycle as well as treat the scale insects themselves.

Integrated Control: Break the Ant-Scale Cycle

Successful control of scale insects in presence of attending ants requires a dual-focus strategy: ant management + scale insect treatment.

Cultural & Physical Measures

• Prune branches or vegetation that provide direct pathways for ants into the canopy (e.g., tree limbs touching fences or buildings).

• Install sticky bands or physical trunk barriers (tamper-resistant sticky tape or commercial ant-barrier products) around tree trunks and structures to impede ant access to foliage.

• Eliminate ant nests or food sources near the plants: reduce debris, vegetation near walls, mulch close to trunks, weeds or alternate sugar sources.

• Wash honeydew and scale residue from leaves and branches to reduce the ant “reward” and improve spray or treatment coverage.

Biological Measures

• Encourage natural enemies of scale insects: parasitic wasps (Encyrtidae, Eulophidae), predatory lady beetles, lacewings. These beneficials have less impact when ants protect the scales, so ant control enhances biological efficacy.

• Maintain habitat features that support beneficial insects: flowering plants, minimal broad-spectrum insecticide use, good plant health for strong natural enemy populations.

Chemical Control (Including Active Ingredients)

When cultural and biological controls are insufficient, chemical options targeted at scale insects (and sometimes ants) can be integrated—always following local registration, label instructions and safety practices.

• For scale insects: Insecticides or treatments include horticultural oils and insecticidal soaps timed at the crawler stage (when young scale insects are unprotected). Also systemic actives (for example imidacloprid, thiamethoxam, spirotetramat, buprofezin) may be used on larger plants or mature infestations where allowed.

• For ants: Use of ant baits, barrier products or labeled ant-control insecticides near nests/trails helps suppress ant attendance and thereby reduces protection of scale insects.

• Use a rotation of modes of action for scale insect active ingredients to avoid resistance.

• Ensure that the chosen product is labeled for scale insects on the specific host plant, in the specific region, and for the scenario (indoor vs outdoor, shrub vs tree).
  By combining ant control and targeted scale treatment, the overall effectiveness improves and the pest-plant system is weakened more rapidly.

Why a Combined Strategy Works Better

Controlling only scale insects without addressing ant attendance often leads to short-term gains followed by relapse. The ant-scale symbiosis means that as long as ants protect the scales, even effective sprays or treatments may be undermined. On the other side, controlling ants alone without treating the existing scale insects leaves the pest population active, and new crawlers will simply regenerate. A combined strategy that disrupts ant access, treats scale insects at vulnerable life stages, and enhances natural enemy activity yields longer-term success and fewer interventions.

Summary & Next Steps for Practitioners

Ants rarely act as predators of scale insects in managed landscapes; instead they enable the scale insects to thrive. For effective management:

• Monitor for signs of ant–scale partnerships (honeydew, ants, scale shells).

• Install physical barriers and reduce ant access to plants.

• Time scale insect treatment to crawler stage and select appropriate active ingredients or oils/soaps.

• Use chemical treatments for scale insects only when needed and ensure they are approved for the specific crop/host plant and region.

• Train your team (service providers, distributors) on both ant and scale insect monitoring so that programs reflect the full cycle of interaction.