We experience more mosquito bites at night. Why?

K. ANANTHANARAYANAN

Kanyakumari, Tamil Nadu

May be because during the night we are drowsy, our reflexes are down and we may not swat the mosquitoes immediately after their bite (before they have completed their meal).

Theories apart, mosquitoes are crepuscular, most active during dawn and dusk. Being ectothermic, they seek warmth but are actually quite vulnerable to hot, dry conditions, and can easily overheat and dessicate in direct sunlight.

Mosquitoes generally do not like intense light, intense cold and windy conditions and so are most comfortable, become more active during dawn and dusk . polarised light, Change in CO concentration in the atmosphere and quiet wind velocities during dawn and dusk might be the triggers for mosquito activities.

UV Light (polarized light) is more predominant during dawn and dusk than infra red light and Mosquitoes are known to be attracted to and using UV light to find damp water sources. Infra red light which is more intense during day time is known to curtail mosquito activity.

While the dawn activity is brief as the heat and intensive light increases as the day progresses, the dusk activity gets prolonged well into night because of the increased efficiency of mosquito’s thermal and odour receptors during late evenings and early nights due to humid conditions. While in the day time the thermal receptors detect their victim at about 3 metres away, the efficiency increases three-fold during humid night time.

The odour receptors can detect their target victim at over 100 metres during the night and at more distances if the intended victim is big or pregnant exhaling more CO and has sweetish smell or had a pint of beer.

Mosquitoes do not bite only during the night hours. They can however if roused bite any time of the day irrespective of weather conditions. Certain species of mosquitoes are only active during the daytime, and in most cases, daytime feeders are a great deal more aggressive than night-time feeders.

Dr. A. Chandrasekaran

Veterinarian and Animal Behaviour Consultant

Coimbatore, Tamil Nadu

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