GRAND CAYMAN, Cayman Islands (4 August 2026) – The Mosquito Research and Control Unit (MRCU) continues extensive mosquito control operations as biting mosquito numbers remain higher than the Unit considers acceptable in several areas of Grand Cayman.
MRCU’s surveillance data confirm a significant seasonal increase. Preliminary figures for 2026 show a year-to-date average of approximately 40 mosquitoes per trap night, compared with approximately 29 in 2025. However, this remains below the average recorded in 2023, when the figure was approximately 57 mosquitoes per trap night, as well as several of Cayman’s more severe historical years.
Daily trap collections also show separate waves of mosquito activity. The highest daily total recorded during the past 180 days exceeded 9,000 mosquitoes in June. Numbers subsequently declined before rising again in July, when a daily total of more than 5,000 mosquitoes was recorded.
These figures demonstrate that current mosquito activity is significant, but not unprecedented. They also show how numbers can rise and fall quickly as different sections of wetland are flooded and separate generations of mosquitoes emerge.
Trap data are one of several tools MRCU uses to guide operations. Teams also consider field inspections, biting activity, tidal conditions, rainfall, weather forecasts and the results of previous treatments when determining where and when operations should take place.
Tidal flooding driving current activity
Much of the mosquito activity experienced this season is linked to extensive tidal flooding across Cayman’s wetlands.
Elevated tides have repeatedly pushed water into large areas of low-lying wetland, including locations that may remain dry for extended periods. This creates ideal conditions for large numbers of dormant mosquito eggs to hatch at approximately the same time.
The primary mosquito responsible for the current emergence is Aedes taeniorhynchus, commonly known as the black salt marsh mosquito. This species lays its eggs in damp wetland soil rather than directly on the surface of the water. The eggs can remain dormant for months or longer while waiting for the area to flood.
When tides or heavy rainfall cover the eggs with water, they hatch and the mosquitoes begin developing in the flooded wetlands. Several days later, large numbers can emerge within a relatively short period.
Aedes taeniorhynchus is a very aggressive biter and a strong flyer. Mosquitoes emerging from the wetlands can travel several miles into surrounding residential and commercial areas.
When this species is present in high numbers, the mosquitoes also tend to shelter during the day in shrubs, vegetation and other shaded locations. As a result, daytime biting can increase, particularly around gardens, trees, hedges and other shaded areas.
While this species is not known to transmit human disease locally, it can transmit heartworm disease to dogs and cats. Pet owners are therefore encouraged to ensure their animals remain protected through appropriate heartworm prevention.
Cayman has extensive natural wetlands where this mosquito breeds. Across these habitats, the number of dormant eggs can reach into the trillions. This means that even after extensive preventative treatment, a relatively small percentage surviving can still result in a noticeable emergence.
Videos showing some of the tidal flooding currently affecting Cayman’s wetlands can be viewed on MRCU’s social media pages.
Prevention does not mean zero mosquitoes
MRCU carries out extensive larviciding to reduce mosquito populations before they emerge. These treatments prevent enormous numbers of mosquitoes from reaching the adult stage, but no mosquito control programme can reach every egg or treat every section of Cayman’s vast and environmentally sensitive wetlands.
There will always be seasonal periods when mosquitoes emerge, regardless of the proactive work carried out by MRCU. This is a natural consequence of living in a tropical coastal environment with extensive wetland habitat, and it is not unique to the Cayman Islands.
Similar seasonal emergences occur in coastal communities around the world. What distinguishes Cayman is the scale and sophistication of the mosquito control programme developed here over several decades.
Before organised mosquito control, mosquito populations regularly disrupted outdoor activity, daily life and Cayman’s development. Today, MRCU operates an advanced programme that includes mosquito surveillance, scientific research, larviciding, aircraft operations, truck fogging, resistance monitoring and public education.
Without these interventions, the mosquito numbers produced by major tidal flooding events would be considerably higher.
Numerous operations continue
MRCU has carried out numerous aerial and ground-based mosquito control operations in recent weeks, alongside daily surveillance, field inspections and preventative treatments.
Some residents have questioned why they may not see the aircraft or truck foggers operating in their area every night. While members of the public may not personally observe every operation, work continues across multiple sections of MRCU each day.
A treatment in a particular area also does not mean that the same area can or should be treated again the following night. All mosquito control products must be used strictly in accordance with their approved labels. Depending on the product and type of treatment, the label may require an interval of several days between applications.
Following these requirements helps protect people, wildlife and the wider environment.
MRCU must also carefully manage how frequently different products are applied. Using the same product too often can increase the risk of mosquitoes developing resistance, potentially making that product less effective over time.
Effective mosquito control therefore requires a careful balance between responding to current biting levels, following product labels, protecting the environment and preserving the long-term effectiveness of the products available.
Temporary drone programme setback
MRCU has experienced a setback with its application drone programme and currently has no application drones available for mosquito control.
While this temporarily limits one of the treatment methods available to the Unit, it has not interrupted MRCU’s wider mosquito control programme. Aircraft operations, truck fogging, larviciding, surveillance and field activities continue, while work is underway to restore application drone capability for future operations.
Operations will continue
MRCU recognises the frustration caused by the current biting levels and is not satisfied with mosquito numbers remaining above acceptable levels.
Teams will continue monitoring mosquito populations and adjusting operations based on surveillance results, tidal activity, weather conditions and the effectiveness of previous treatments.
Residents are encouraged to use an effective mosquito repellent, particularly around sunrise and sunset and when spending time near shaded vegetation. They should also maintain window and door screens and ensure dogs and cats remain protected against heartworm.
MRCU appreciates the public’s patience and understanding as teams continue working to bring seasonal mosquito numbers back to more acceptable levels.