The small, dark, flying insects hovering around your aloe plant are likely fungus gnats (family Sciaridae). While the adult gnats, which resemble tiny mosquitoes with dark bodies and long legs, are mostly a nuisance, their presence indicates a deeper problem within the soil. The adult stage, measuring about 2 to 4 millimeters, does not directly harm the plant but continues the destructive life cycle.
The real damage is caused by the translucent, worm-like larvae living in the top layer of the potting mix. These larvae feed primarily on fungi and decaying organic matter, a symptom of consistently damp conditions. They also feed on delicate roots, particularly the fine root hairs of young or stressed plants. This root damage can lead to yellowing leaves, stunted growth, and, in severe cases, the death of the aloe plant. Eliminating these pests requires adjusting your care routine to remove their breeding ground.
Identifying the Invader and the Root Cause
The tiny flies associated with houseplants are almost always fungus gnats, which are physically distinct from fruit flies that are attracted to fermenting produce. Fungus gnats have slender, dark gray or black bodies and long, spindly legs, giving them a mosquito-like appearance. They are weak, erratic fliers that stay close to the soil surface. Fruit flies, by contrast, have a rounder, tan-to-brown body and bright red eyes.
The root cause of a fungus gnat infestation is consistently moist soil, which is problematic for aloe plants. As a succulent, aloe is adapted to arid conditions and thrives in soil that dries out quickly and completely between waterings. When the soil remains wet, it creates an ideal environment for the fungi and algae that the gnat larvae consume. This moisture allows the gnat life cycle—egg, larva, pupa, and adult—to complete quickly. A female gnat can lay up to 300 eggs in damp soil, ensuring a continuous population boom.
Eradicating the Infestation: Immediate and Long-Term Solutions
Effectively eliminating the infestation requires a two-pronged approach that targets both the flying adults and the damaging larvae in the soil. Adult removal is necessary to break the reproductive cycle and prevent new eggs from being laid.
Targeting Adult Gnats
The simplest physical method is using yellow sticky traps, which are highly attractive to the adults. The gnats get stuck and die before they can reproduce.
You can also set out a liquid trap by mixing apple cider vinegar with a drop of dish soap in a shallow dish near the plant. The vinegar attracts the adult gnats, and the soap breaks the surface tension of the liquid, causing the insects to drown. While these methods reduce the adult population, they do not address the hundreds of larvae developing in the soil.
Eliminating Larvae in the Soil
Treating the soil to eliminate the larvae is the most crucial step for long-term control. A popular and accessible treatment is a soil drench using a diluted hydrogen peroxide solution, typically one part 3% hydrogen peroxide mixed with four parts water.
When poured onto the soil, this mixture fizzes as it contacts the larvae, killing them on contact by oxidizing them. The solution quickly breaks down into harmless water and oxygen.
For a more targeted biological control, apply products containing the naturally occurring bacterium Bacillus thuringiensis subspecies israelensis (Bti). This bacterium is often found in mosquito control products.
When Bti is applied as a soil drench, the gnat larvae ingest the bacteria. This produces a toxin that specifically disrupts their digestive system, leading to their death within a few days. This method is effective and safe for the aloe plant.
Adjusting Aloe Care to Prevent Recurrence
Once the active infestation is under control, the focus must shift to maintaining an environment inhospitable to fungus gnats. Revising your watering habits is the most important preventative measure for an aloe plant.
Only water the aloe when the soil has completely dried out several inches down, not just at the surface. When watering, soak the soil thoroughly, but ensure all excess water drains out immediately. Never allow the pot to sit in a saucer of standing water.
Aloe plants require a fast-draining potting mix, ideally a gritty succulent or cactus mix. This mix should contain materials like perlite, coarse sand, or pumice to prevent soil compaction and water retention. A heavy, peat-based mix holds moisture too long, inviting the gnats back.
Sanitation is also an important preventative practice. Regularly remove any dead or fallen aloe leaves from the soil surface, as this decaying organic matter feeds gnat larvae. You can also place a top dressing of sand, fine gravel, or an inert material over the soil to create a dry barrier that discourages adult females from laying eggs in the potting mix.