You start your mosquito trap and for the first couple of weeks, the catch was quite staggering. Almost to empty basket, but still getting bit. Don’t assume that the trap is broken before you try to fix it; in most cases, a decline in catch is correctable. Below are the most common causes, and a solution to each.

1. The Number of Mosquitoes Has Actually Increased

Not All Declines in Catch Are Trap Issues

Mosquitoes increase and decrease in numbers due to variations in temperature, rainfall and seasons. A cool snap or a period of drought may severely reduce the local population, or the end of the breeding season.

Your trap could just be working in less of a buzzed about neighborhood if your neighbors are seeing a decline in mosquitoes as well.

What to do: Compare against the weather and the time of year before troubleshooting. A low number is normal if it is late fall or an abnormally dry week.

2. The Attractant Is Used Up

The majority of traps, including a CO2 mosquito trap, use a lure, for example CO₂ (from a propane cylinder), an octenol cartridge or a UV light and chemical attractant. They are not perennial.

Propane-powered CO2 mosquito traps cease to generate CO₂ when the tank is empty. Depending on the product, octenol or lure cartridges will lose their effectiveness after 2 to 4 weeks. UV bulbs can become dimmed even when they appear to be “lit”.

What to Do

Consult the manufacturer’s replacement schedule and replace lures and bulbs according to the schedule. A declining catch, at more or less regular intervals over the month, is almost always indicative of an out-of-date attractant.

3. The Trap Is in the Wrong Spot

Placement is more important than many would think. The catch can be doubled or trebled with a good location.

Common Placement Mistakes

Placing the trap within a short distance from where people sit. It should repel mosquitoes away from you, so position it 20 to 40 feet away from patios and where people gather.

Setting it out in the open, in the wind. The scent plume is blown away by the wind and the mosquitoes are unable to follow it back to the trap.

Moisture and darkness are favorable for the growth of mosquitoes: hang it in full direct sun.

Placing it too far up. Most species of flies are low fliers and therefore the trap is most effective at 3 to 6 feet above the ground.

What to Do

Position the trap in areas where mosquitoes rest and/or breed (shaded shrubs, tall grass, wet areas) but upwind from where they are working.

4. Competing Attractants Nearby

Mosquitoes will always use the strongest signal. You will win the competition for attention if you, your pets or a neighboring group of humans are producing more CO₂ and body heat than the competition. Dense foliage, compost piles, and standing water will also attract mosquitoes.

What to Do

Avoid having the trap in outdoor seating areas and minimize the standing water in the yard so it is not competing for the trap.

5. The Trap Is in Need of Cleaning or Maintenance

A dirty trap will not function as well. Dead insects can block fans, intake openings and cover up the attractant. If the fan is weak, it will not draw in mosquitoes and if the collection chamber is full or sticky, mosquitoes may be repelled from entering.

What to Do

Regularly empty collection basket.

Wash intake/fan area to get rid of dirt and cobwebs.

Gently rotate the fan to make sure it moves freely and that the power plug is secured.

Check hoses and fittings for obstructions or leaks (particularly CO₂ models).

6. Problems With Power or Fuel

The trap may appear to be running and yet it is not being as effective as it could be. The fan speed can be lowered due to low batteries, a failed power adapter or an unsealed cord. Damage to the propane regulator or tubing, or when the propane tank has a low propane level, can cause gas flow loss with propane models.

What to Do

Check to see if the fan is operating at maximum speed; replace batteries or check connections. Test propane traps on the tank, regulator and gas line.

7. The Trap Is Correct but for the Wrong Species of Mosquito

Each mosquito species has its unique characteristics. Aedes spp., including the Asian Tiger mosquito, bite during the day and are less attracted to some lights and CO₂ configurations. Culex mosquitoes are most active during the day in the late hours of the day and night. Some traps that are effective for one species may not be as effective for another and mixes of species vary across the season.

Action to Take

Research a trap that is specific to the species found in your region and see if the manufacturer has any specific day-biting mosquito lures or settings.

8. You’re Not Giving It Enough Time

Traps are used to work by gradually decreasing the population, especially breeding females in the area. A trap can catch many mosquitoes in the early stages but will catch less mosquitoes as the population of mosquitoes nearby diminishes. That’s what it’s meant to do, in fact. The drop will not indicate a failure of the device, but rather a reduced number of mosquitoes to be captured.

9. Breeding Sites Are Filling Up the Population

If the mosquitoes in your yard are hatching constantly, the trap can’t catch them all. Larvae can develop in even a small standing water in a bottle cap.

What to Do

Clean or fill plant saucers, birdbaths, toys and buckets weekly.

Remove debris from gutters and repair drainage issues.

If you must have standing water, treat it with larvicide (e.g. Bti dunks).

Combined with source reduction, a trap will work much better than a trap alone.

Quick Troubleshooting Checklist

Are the right conditions for mosquito season and weather?

Does the lure or the gas or the bulb smell new?

Is trap clean and fan operating at full speed?

Is it in a shaded, low, sheltered area, out of the way of the sitting area?

Have you removed any standing water from your property?

Does the trap attract the mosquito species in your area?

Final Thoughts

A trap that collects less mosquitoes can not be said to be broken. Usually, the answer is a simple one – the lure has expired, the location is not ideal, there’s a dirty fan filter or a natural shift in the mosquito population. Follow the steps listed above and in many cases you’ll recover your catch rate. Your trap should be used in conjunction with regular yard maintenance to eliminate mosquitoes at the source, for best results.