Mosquito larvae are the immature, aquatic stage of the mosquito life cycle, occurring before they develop into flying, biting adults. Identifying these organisms is the first step in effective pest control. Since they spend their entire existence in water, recognizing their appearance and behaviors is necessary for preventing the emergence of the next generation of mosquitoes. Often called “wrigglers,” their presence indicates a nearby breeding site that should be addressed.
Detailed Physical Characteristics
A mosquito larva is distinctly worm-like, typically reaching up to about half an inch in length. The body is divided into three main sections: a well-defined head, a swollen, unsegmented thorax, and a long, narrow abdomen. Larvae are often translucent, white, gray, or brown, depending on the species and water quality.
A defining feature for most species is the respiratory siphon, a tube-like structure at the end of the abdomen used to breathe air from the water’s surface. They hang upside down from the water tension, using the siphon like a snorkel, while filtering algae and microorganisms for food. Larvae of the Anopheles genus are an exception; they lack a siphon and lie parallel to the water surface to breathe. Larvae pass through four developmental phases, or instars, molting their skin before transitioning to the next life stage.
Typical Habitats and Behaviors
Mosquito larvae require stagnant water to survive, inhabiting any container that holds still water for more than a few days. Breeding sites range from small containers like bottle caps to larger areas like ornamental ponds, clogged gutters, old tires, bird baths, and rain barrels. Their characteristic movement earned them the nickname “wrigglers.”
When disturbed, a larva quickly disengages its siphon and moves downward in a jerky, wriggling motion to evade threats. They spend most of their time near the surface to access air, while constantly feeding on organic debris. The larval stage typically lasts between four and fourteen days, with warmer water temperatures accelerating development.
The Next Stage: Pupae
Following the larval stage, the mosquito transforms into a pupa, a phase that typically lasts between one and four days. The pupa has a dramatically different appearance from the larva, characterized by a large, rounded head and thorax fused into a single unit. The abdomen is curled underneath, giving it a comma or C-shaped profile, which is why pupae are commonly referred to as “tumblers.”
Unlike the larva, the pupa does not feed, focusing entirely on the internal reorganization needed to become an adult mosquito. It breathes through a pair of small respiratory tubes, called trumpets, located on the fused head and thorax. The pupa is highly mobile and will tumble rapidly downward when disturbed.
Eliminating Larvae
The most effective way to eliminate mosquito larvae is by removing their habitat, a process known as source reduction. This involves physically dumping out standing water in containers, old equipment, or garden saucers, and scrubbing the sides to remove eggs. When water features like ponds or rain barrels cannot be drained, targeted treatments are necessary.
For water sources that cannot be emptied, a biological control agent is a safe and effective option. Products containing Bacillus thuringiensis israelensis (Bti) are common, as this naturally occurring bacterium is only toxic to mosquito larvae and related flies. Larvae ingest the Bti spores while feeding, which releases toxins that damage their gut lining, causing them to die within 24 to 48 hours. Bti is widely available in granular, liquid, or briquette forms applied directly to the water surface.