A mosquito larva is the aquatic, immature stage in a mosquito’s life, entirely dependent on water for survival. Commonly called “wrigglers,” these tiny, worm-like creatures are seen moving just below the surface of still water. Their characteristic writhing motion is how they move and evade threats. Although they live in water, most larvae must frequently come to the surface to breathe air.
The Mosquito Life Cycle
All mosquitoes undergo a four-stage life cycle: egg, larva, pupa, and adult. This process begins when a female mosquito lays her eggs on or near a water source. Depending on the species, eggs are laid either individually or in attached groups that float on the water’s surface, resembling tiny rafts. Within a couple of days, these eggs hatch, releasing the larvae.
The larval stage is dedicated to growth and feeding, which can last from four to fourteen days depending on water temperature and food availability. During this period, the larva will molt its skin four times in phases called instars. After the fourth instar, the larva transitions into the pupa, a non-feeding stage where it transforms into its adult form. The full cycle from egg to adult can take as little as ten days or up to a month in cooler conditions.
Identifying Larvae and Their Habitats
Mosquito larvae have a segmented, worm-like body with a large head and thorax and a narrower abdomen. They are about 1/4 inch long, lack legs, and are often seen hanging upside down just beneath the water’s surface. This position allows them to extend a small breathing tube, called a siphon, to take in oxygen. When the water is disturbed, they will quickly wriggle downward to escape.
Since larvae require a stagnant water environment, they can be found where water collects and remains still. They cannot survive in moving water like streams or rivers because they need the calm surface to breathe. Common man-made habitats include clogged gutters, birdbaths, flowerpot saucers, and discarded tires. Natural breeding grounds consist of temporary puddles, marshes, and ponds where they feed on algae and microorganisms.
Methods for Controlling Mosquito Larvae
The most effective approach to managing mosquito populations is to target the larval stage by eliminating their aquatic habitats, a method known as source reduction. Regularly empty any containers that hold standing water to prevent larvae from developing. This includes turning over buckets, cleaning out clogged rain gutters, and refreshing the water in birdbaths at least once a week.
For bodies of water that cannot be easily emptied, such as ornamental ponds or rain barrels, biological controls are an option. Products containing Bacillus thuringiensis israelensis, or Bti, are widely available as dunks or granules. Bti is a naturally occurring bacterium that produces proteins toxic only to the larvae of mosquitoes. When larvae ingest the Bti, it destroys their digestive system, killing them within a few days, and is safe for humans, pets, fish, and other wildlife.
In larger ponds, introducing natural predators can also help manage larval populations. Mosquito fish, such as Gambusia affinis, are voracious consumers of mosquito larvae and can be added to contained water gardens. Enhancing the environment for other natural predators like dragonflies also helps. Additionally, adding a fountain or waterfall to a pond increases water circulation, which disrupts the still surface larvae need to breathe.