Mosquito larvae, nicknamed wrigglers, are the second of four life stages and live entirely in standing water. To kill them, remove standing water and treat water you cannot drain with Bti, a natural larvicide that stops larvae before they become biting adults.
If you have found thin, thrashing worms in a birdbath, bucket, or clogged gutter, you are almost certainly looking at mosquito larvae. Understanding them is easiest through one clear framework: the Empty-or-Treat rule. Because larvae can only develop in standing water, you either empty that water or treat it with a larvicide. Get that right and you break the mosquito life cycle before a single new adult can fly.
What Mosquito Larvae Look Like (Wrigglers)
Mosquito larvae are the stage that hatches from mosquito eggs, and they earn the nickname wrigglers from the way they whip and thrash through the water when disturbed. They look like small, thin worms, and most hang just below the surface of standing water, breathing air through a tube at the tail. Both the larva and the stage that follows it, the pupa, live in water — a key reason the CDC and EPA point to standing water as the place to focus mosquito control.
The pupa has its own nickname: the tumbler, because it tumbles and rolls through the water when disturbed instead of feeding. Unlike the larva, the pupa does not eat; it is a resting, transforming stage before the adult emerges. Only female mosquitoes go on to bite, because they need a blood meal to produce eggs, while males feed on nectar. To see how long those adults last once they leave the water, see how long do mosquitoes live.
The Mosquito Life Cycle
Mosquitoes develop through four stages: egg → larva (wriggler) → pupa (tumbler) → adult. The larva and pupa both live in water, and the adult is the flying, biting stage. The full cycle from egg to adult typically takes about two weeks, but according to the EPA it can range from as little as 4 days to a month depending on conditions such as temperature — warmer water speeds it up.
The exact timing depends on the mosquito. According to the CDC, egg-to-adult development runs about 7 to 10 days for Aedes and Culex mosquitoes and about 10 to 14 days for Anopheles. Because that window can be so short in warm weather, even a container that holds water for a week can produce a new generation of adults.
Larvae and pupae both live in water, so removing standing water breaks the cycle. Figures: CDC and EPA.
How to Kill Larvae (Bti & Water Removal)
Because larvae cannot survive outside water, control comes down to two moves. The first and most effective, per the CDC and EPA, is to eliminate standing water so larvae have nowhere to develop. The second is to treat water you cannot drain with Bti, a natural larvicide that kills larvae before they reach the biting adult stage. For a deeper walkthrough of both, see how to get rid of mosquitoes.
Break the Larval Cycle
Larvae need standing water. Remove it or treat it:
Empty standing water weekly — saucers, buckets, clogged gutters, old tires, and birdbaths. Emptying interrupts the larval cycle before larvae mature.
Treat water you cannot drain with Bti — Bacillus thuringiensis israelensis in mosquito dunks or bits kills larvae in the water and, per the EPA, is not harmful to people, pets, or beneficial insects.
Bti is the active ingredient in the products covered in mosquito dunks.
Timing matters because the cycle is fast. With egg-to-adult development as short as 4 days in warm conditions, refreshing birdbaths and dumping containers on a weekly schedule keeps larvae from ever reaching the pupa and adult stages. For a full overview of mosquito biology and control, start with the mosquitoes hub.
Frequently Asked Questions
What are mosquito larvae?
Mosquito larvae are the second stage of the mosquito life cycle, often called wrigglers because of the way they thrash through the water. They hatch from eggs and live entirely in standing water, feeding on tiny organic matter until they develop into the pupa stage. Larvae and pupae both live in water, which is why removing standing water is the most effective way to control mosquitoes.
What do mosquito larvae look like?
Mosquito larvae look like small, thin worms that hang just below the surface of standing water and wriggle when disturbed, which is why they are nicknamed wrigglers. Most breathe air through a tube at the tail, so you will often see them suspended head-down at the surface. The next stage, the pupa, is comma-shaped and is nicknamed the tumbler because it tumbles through the water when disturbed.
How long do mosquito larvae take to become adults?
The full life cycle from egg to adult typically takes about two weeks, but it can range from as little as 4 days to a month depending on conditions such as temperature. According to the CDC, Aedes and Culex mosquitoes go from egg to adult in about 7 to 10 days, while Anopheles mosquitoes take about 10 to 14 days. Warmer water speeds development up.
How do you kill mosquito larvae?
The two most reliable methods are removing standing water and treating water you cannot drain with Bti, a natural larvicide. Emptying containers, buckets, clogged gutters, old tires, and birdbaths breaks the larval cycle before larvae can mature. For water that stays, Bti (Bacillus thuringiensis israelensis) in mosquito dunks or bits kills larvae in the water and is not harmful to people, pets, or beneficial insects.
Where do mosquito larvae live?
Mosquito larvae live in standing water. Even small amounts of water in containers, saucers, buckets, clogged gutters, tires, or birdbaths can host them. Because larvae and pupae both develop in water, eliminating standing water is the single most effective mosquito control step recommended by the CDC and EPA.
Is Bti safe for people and pets?
Yes. Bti (Bacillus thuringiensis israelensis) is a naturally occurring bacterium used as a larvicide in mosquito dunks and bits. It targets mosquito larvae in the water and, according to the EPA, is not harmful to people, pets, or beneficial insects when used as directed. It is a common choice for treating water features and containers that cannot be drained.
How often should I empty standing water to stop larvae?
At least once a week. Because mosquitoes can go from egg to adult in as little as 4 days under warm conditions, emptying and refreshing water in birdbaths, saucers, and buckets on a weekly schedule interrupts the larval cycle before larvae reach adulthood. For water that cannot be emptied, use Bti to kill larvae in place.
Sources
CDC — About Mosquitoes (four-stage life cycle; larvae and pupae live in water; only females bite).