Ladybugs, also known as lady beetles, are a familiar sight in gardens and a common choice for gardeners seeking natural methods of pest control. These small, brightly colored insects are widely recognized for their beneficial role in agriculture and home gardens. This popularity often leads to questions about which pests these helpful beetles can manage, particularly the small, flying insects known as gnats.
Do Ladybugs Eat Gnats
Ladybugs are not considered an effective method for controlling gnat populations, especially the common fungus gnats that plague houseplants. Fungus gnats (often Bradysia impatiens) lay their eggs in the top few inches of moist soil, and their larvae feed on organic matter and delicate plant roots beneath the surface. Ladybugs, both adults and larvae, primarily hunt on plant foliage, stems, and flowers, which means they rarely encounter the gnat larvae where the real damage is done.
While an adult ladybug may occasionally consume a slow-moving adult fungus gnat flying near the plant, this is not a significant part of their diet or life cycle. The adult gnats are small, fast-moving, and do not provide the substantial, soft-bodied meal a ladybug seeks. Relying on ladybugs to manage an established gnat problem will likely result in continued infestation because the bulk of the pest population—the larvae—remains safely underground, continuing the breeding cycle.
Ladybugs Preferred Diet
Ladybugs are specialized predators with a diet focused on soft-bodied, slow-moving pests that feed on plant sap. Their main food source is aphids, and a single adult ladybug can consume dozens of aphids in a day.
Beyond aphids, their diet commonly includes scale insects, mealybugs, and spider mites, which are all found clinging to plant stems and leaves. The larval stage of the ladybug is often a more voracious hunter than the adult beetle. Ladybug larvae have a high metabolic need for protein to fuel their rapid growth, making them effective pest controllers during this stage.
Effective Gnat Management
Since ladybugs do not provide meaningful control, effective gnat management requires targeting the larval stage in the soil. The most important step is environmental control, specifically by allowing the top one to two inches of soil to dry out completely between watering sessions. Fungus gnat larvae require consistently moist soil to survive, so a dry top layer reduces the number of eggs laid and the survival rate of the hatched larvae.
Biological and Physical Controls
For direct biological control, applying Bacillus thuringiensis israelensis (Bti) is effective. Bti is a naturally occurring bacterium mixed with water and applied to the soil, where it kills gnat larvae upon ingestion. Yellow sticky traps can also be placed near plants to capture adult gnats, reducing the number of egg-laying females. Another option is the introduction of beneficial nematodes, such as Steinernema feltiae, which are microscopic worms that hunt and kill the larvae in the soil.