The common sight of ants crawling on a plant struggling with tiny pests naturally leads to the question of whether the ants are there to help. Gardeners often observe ants near an infestation of spider mites, those nearly invisible arachnids that damage foliage. This article clarifies the distinct relationship between these two organisms and explains the true reason ants are often found on mite-infested plants.
Identifying Spider Mites and Ant Presence
Spider mites are tiny arachnids, related to spiders and ticks, making them resilient to many common insecticides. Infestations are often first noticed by the damage they cause, which appears as fine, pale stippling on the leaves where the mites have sucked out the plant’s chlorophyll. As the population grows, the mites spin fine, silky webbing, typically on the undersides of leaves and between stems, which serves as protection for the colony and its eggs.
An ant presence is usually marked by a distinct trail of workers moving up and down the plant stem or along branches. These scent-marked paths allow the social insects to efficiently forage for food and return to their nest. While ants may build nests near the base of an outdoor plant, their activity on the foliage is specifically for food collection.
The Direct Answer: Do Ants Prey on Spider Mites?
Ants are generalist foragers with a varied diet including sugars, fats, and protein. However, most common garden ant species do not actively hunt and consume spider mites as a primary food source. Spider mites are extremely small, typically less than half a millimeter long, and are often protected by dense webbing, making them difficult targets for ants.
Mites lack the high caloric reward that ants seek, such as concentrated sugars or the protein mass of a larger insect. The effort required for an ant to navigate the mite’s web and capture such a tiny organism does not justify the minimal nutritional gain. Ants will ignore the spider mites entirely while foraging on the plant.
Rarely, specific ant species, such as the ghost ant (Tapinoma melanocephalum), have been documented as predators of spider mites in controlled environments. These instances are exceptions and usually occur when ants have a strong need for protein and other food sources are scarce. Studies show that some spider mites actively avoid the chemical traces left by ants, suggesting an evolutionary pressure to steer clear of these potential predators.
Ant Behavior: Why Ants Are On the Plant
If ants are not eating the spider mites, their presence on an infested plant strongly suggests a co-occurring pest problem. The primary reason ants climb plants is to collect honeydew, a sugary liquid waste product excreted by other sap-sucking insects. This mutualistic relationship, known as trophobiosis, means ants gain a reliable food source while protecting the pests from natural enemies.
Honeydew is produced by pests like aphids, scale insects, and mealybugs, which are often found alongside spider mites. The ants “tend” these insects, guarding them against predators such as ladybugs and parasitic wasps, ensuring a continuous supply of the sweet excretion. This protection allows the pest population to flourish, causing greater damage to the plant.
The presence of ants acts as a warning sign that the plant is under attack by a complex of pests, not just spider mites. By protecting these insects, ants inadvertently worsen the plant’s overall health by allowing a secondary infestation to intensify. Some research indicates that ants tending aphids may prey on spider mites, reducing the mite population as a side effect of their guarding activity, not due to a direct preference.
Effective Management of Spider Mites
Since ants are not a reliable biological control agent for spider mites, management must focus on direct methods.
Physical Removal
Initial control efforts should be non-chemical and involve physically removing the pests from the plant. A forceful jet of water from a hose or spray bottle can dislodge a large number of mites and destroy their protective webbing. This method is most effective when directed at the undersides of the leaves where the mites congregate.
Horticultural Treatments
For more persistent infestations, horticultural treatments offer a low-impact solution. Insecticidal soap and neem oil are highly effective because they work by contact, coating and smothering the tiny arachnids. These treatments must be applied thoroughly to all plant surfaces, including the undersides of leaves, and may require repeat applications every few days to kill newly hatched mites.
Biological and Environmental Control
Long-term management can be achieved by introducing natural predators that specialize in consuming spider mites, such as predatory mites (Phytoseiulus persimilis) or lacewing larvae. Maintaining plant health by avoiding water stress and keeping humidity levels higher also helps to deter new infestations. Spider mites thrive in hot, dry conditions, so environmental control is key.