South Carolina is home to at least 61 different species of mosquitos, providing a food source for birds, fishes, frogs, bats, and other animals. Mosquitos are close relatives of flies in the gnat and no-see-um taxa. The term mosquito means “little fly”, indicating that they are a midge-like, two-winged insect. Mosquitos complete their life cycle in four stages: egg, larva, pupa, and adult. The availability of standing water is integral to these life stages and highly influential on the overall number of mosquitoes produced. Water allowed to “stand” for five days or more can become a mosquito-breeding site.
Adult female mosquitos produce eggs that are deposited in stagnant water to develop. Capture and retention of water in an area or location can be unlimited, allowing mosquitos the advantage of high reproductive success. Large populations of mosquitos rapidly become a nuisance or worse. Mosquitos are most noted for the itchy bite they inflict upon contact but are also known to be potential vectors of disease.
South Carolina’s Department of Health and Environmental Control (DHEC) lists West Nile, Eastern Equine Encephalitis, La Crosse encephalitis, St. Louis encephalitis virus, and dog/cat worm as common diseases that can be vectored by mosquitos. Zika virus has been a recent addition of concern by DHEC; however, “South Carolina has zero total cases as of September 19, 2019.” Zika virus spreads primarily from the infected bite of two mosquito species, Aedes aegypti and Aedes albopictus (Asian Tiger Mosquito). For more information on Aedes albopictus, see HGIC 2471, Asian Tiger Mosquito.
The almost endless availability of standing water for mosquito reproduction, combined with the ability to vector potentially harmful disease, drives the importance to limit breeding sites. Reducing breeding sites is simple, start by identifying potential locations of water retention and eliminate them. Unfortunately, there is a catch; many places where water pools and becomes stagnant are overlooked. Effective, local mosquito management relies on identifying common and uncommon locations that retain water around homes, landscapes, or properties. This, followed by appropriate action by altering individual habits, can help dry up the situation.
Mosquito Biology and the Role of Water
The mosquito life cycle consists of four developmental stages: egg, larva (referred to as the wriggler), pupa (referred to as the tumbler), and the adult. The life cycle, from egg to adult, takes approximately 8-10 days.
Mature female mosquitos generally require a blood meal prior to egg production and can lay masses of 50 to 200 eggs at a time in or on a water source. There are two mosquito egg types: floodwater eggs (laid in water but require a drying period to become viable) and permanent water eggs (require standing water to hatch). For the majority of permanent water mosquito species, the egg, larva, and pupa stages require water for development.
Permanent water eggs hatch in 2-3 days once laid in or on exposed water. After hatching, a series of larval phases (referred to as instars) will occur indicated by molting and an increase in size. For approximately one week, the wrigglers (larvae) will feed on small pieces of settled organic matter in stagnant water. They periodically “wriggle” to the surface of the water to breathe air at this time. After reaching their final instar and feeding stops, the wriggler will begin to take on the comma-shaped appearance of the pupae (tumblers). The tumbler stage lasts approximately two days but can extend up to a week. The adult mosquito emerges, crawls out of the water, and flies once its body parts have hardened. At this time, the adult mosquito is ready to begin mating. Female and male mosquitoes use flower nectar as a carbohydrate (sugar) source for energy. Only female mosquitoes bite, as they require protein from a blood meal prior to producing new eggs.
Identifying Potential Water Retention Locations
Some types of mosquitos only need a tablespoon of water to develop in. One tablespoon of water is the approximate fill size of a bottle cap. Taking the time to identify and eliminate areas of water retention will help lower mosquito numbers.
Unfortunately, it is common for people to leave items, usually larger than a bottle cap, lying around outside homes or properties. An important first step to reducing areas that retain water is simply not to create them. Proper storage of items in and around the home or property reduces the initial potential for water collection. Turning items over so that water drains rather than fills can become a simple practice. Proper disposal of debris and trash reduces the chance of random water retention in the environment.
Perform routine checks for common items or places that hold water.
- flowerpots and collection saucers
- cans, cups, and bottles
- pet bowls
- animal troughs
- buckets, barrels, and drums
- watering cans
- old tires and hubcaps
- birdbaths and fountains
- children’s toys
- trash cans
- unmaintained swimming or kiddie pools
- low lying areas that create puddles
- tire ruts
- woodpiles and tarps covering woodpiles
Practice thinking outside the box regarding uncommon sources of water retention. Suggestions include:
- caps and lids
- outdoor vases (cemeteries)
- plant cuttings rooting in water
- leaf axils and blades of plants of overgrown shrubs
- wading pools
- garden ponds
- rain barrels
- clogged gutters and downspouts
- boats, canoes, and kayaks (especially if uncovered)
- junk vehicles
- discarded appliances
- unsecured plastic sheeting and tarps
- improperly fastened pool covers
- tree or stump holes
- leaf piles
- cut open-ended bamboo used in landscaping
- fire and barbeque pits
- bricks or cement blocks with holes
- unused pipes
- dysfunctional drain ditches, basins, or cisterns
- leaky pipes that pool water
- nonfunctioning storm drains
- air conditioner drain areas
- flat roofs in the shade
- old shoes or boots left outside
- garden tools
- Locate your local recycling center for proper disposal of items
- Use tight-fitting lids on garbage cans and trash receptacles
- Limit cool, damp, dark areas
- Appropriately mow lawns on a regular basis to limit excessive wetness
- Trim overgrown shrubbery
- Eliminate unnecessary vines and weeds
- Drill holes in tire swings to limit water retention
- Empty and store wading pools when not in use (store pool upright on its side to drain if possible)
- Change water in outdoor pet bowls daily
- Change out water in birdbaths once a week
- Place screens over rain barrels to prevent female mosquitos from laying eggs
- Make sure all drains and pipes function properly
- Repair outdoor faucets with leak issues
- “Leave No Trace’, pick up litter and properly discard
The Take Home Message
It is common to hear: “It’s hard to enjoy the outdoors because there are so many mosquitos.” Prior to seeking chemical control options to solve the dilemma, spend time outside reducing areas and items that retain water or maintain high humidity. This worthwhile activity aids in reducing the numbers of mosquitos along with potential problems and helps create positive habits as stewards of the environment.
The combined knowledge of the mosquito life cycle, the role that water plays in it, and the ease with which water can be collected in the environment promote the need for efficient identification of water capture and retention. Whenever possible, manage, reduce, or eliminate locations or items holding water. Avoid water fill or pooling by promoting water drainage. Properly store, remove, or dispose of unwanted items rather than leaving them outside. Secure coverings tightly and use sand, dirt, or cement to fill voids in the landscape or foundations.
In situations where standing water cannot be prevented or drained, consider using mosquito dunks or pellets, containing Bti (Bacillus thuringiensis var. israelensis). These products are a form of biological control used to kill mosquito larvae in fountains, ponds, or birdbaths that need to hold water.
For more information on Bti, see HGIC 2770, Less Toxic Insecticides.
- South Carolina Department of Health and Environmental Control- Protect Your Home Against Mosquitoes
- South Carolina Department of Health and Environmental Control-Recycle Here SC- https://www.scdhec.gov/environment/recycling-waste-reduction/where-recycle-locally