Swamp mosquitoes emerge

Residents venturing outdoors around dusk and dawn may be unusually susceptible to mosquito bites over the next few days.

‘We are currently seeing a significant hatch of the swamp mosquito,’ said Bill Petrie, head of the Mosquito Control Unit (MRCU). ‘It had nothing to do with Hurricane Dean; in fact we got very little rain over the passage of the storm. Unfortunately lightning has kept the spray plane on the ground for a couple of days, so the emergence may be a bit more troublesome than usual.’

The swamp mosquito is about half the size of the grass mosquito and unlike its bigger cousin which breeds in fresh water (typically near homes), the swamp mosquito breeds around mangroves. Its favorite area is apparently the black mangrove belt, which is tidally flushed and is not too salty or too dry, though it does breed in white and red mangrove stands as well.

The swamp mosquitoes can travel remarkably long distances, up to thirty miles, but certainly ten miles. ‘If left uncontrolled it shows up in every single light trap across the Island, they can certainly reach every major population centre,’ explained Dr Petrie, ‘The swamp mosquito is also harder to ‘catch’ than the grass mosquito, which doesn’t fly very far and seems to be more affected by the chemical spray.’

Only female mosquitoes bite people; the blood is used for developing eggs, not for food.

According to Dr. Petrie female mosquitoes have a variety of senses they use to locate a blood meal. They pick up chemical cues, such as body odour. They can also sense the heat given off by a person and the carbon dioxide they breathe out in their breath.

After a blood meal the female rests for a few days while the eggs develop inside her and then she makes the return trip to the mangroves, where each female lays about 150 eggs. If a female mosquito has a ready source of blood (usually cows or horses) close to the mangroves, they can breed and lay eggs more than once in their lives, which lasts only up to two weeks.

‘The mosquito is difficult to wipe out completely from an area of mangroves’ said Dr. Petrie. ‘Winds tend to blow them in different directions and they will re-settle areas that have been persistently targeted by MRCU operations.’

Seventeen different species of mosquito have been identified in the Cayman Islands and the swamp mosquito is the most common variety.

In the year 1974, close to 800 thousand mosquitoes were discovered in a single MRCU light trap in Bodden Town. Today, it is uncommon if ten different mosquitoes are found in a trap and this has been directly as a result of the ongoing eradication efforts of MRCU.

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