A full mosquito must be much heavier than an empty one 鈥� and they can consume a lot of blood. What is it about the mosquito that allows it to carry such a heavy load? And what is the percentage increase in body weight between a mosquito that hasn鈥檛 had a meal of blood and one that has? How does its pro rata load-carrying ability compare with that of, say, a buzzard or vulture, which must also gorge when the opportunity presents itself?
鈥� Only female mosquitoes consume blood, because they need a source of protein and iron to ensure their eggs develop properly. After feeding, a female digests the blood for several days before laying her eggs and setting out to locate another meal. Following each of these, her weight can increase by as much as 300 per cent. In contrast, a vulture can only eat about 10 per cent of its body mass in carrion (up to around 1 kilogram).
Both mosquitoes and vultures must gorge themselves when they get the chance. However, both also need to fly to escape predators, find food and so on, so they can鈥檛 be totally weighed down by what they eat. The difference between their respective food-carrying abilities comes down to size, and particularly the ratio between muscle strength and body mass.
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A muscle鈥檚 strength is proportional to its cross-sectional area, and an animal鈥檚 mass is proportional to its volume. The volume of an animal decreases more sharply than the muscle cross-sectional area as the animal under consideration gets smaller, so a mosquito is 鈥渟tronger鈥� than the much larger vulture and can take on a greater pro rata load. This also explains why other insects, such as ants, can lift objects that are many times their own body mass.
If a vulture ate three times its own body mass 鈥� as a mosquito does 鈥� it wouldn鈥檛 have the strength to lift itself off the ground. In fact, some vultures vomit from their crop (a special food storage sac near their throat) when threatened by a predator to enable them to make a speedier getaway.
Sam Buckton, Chipperfield, Hertfordshire, UK
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