Millennium Post

Stripes: Camouflage from flies

Stripes: Camouflage from flies
How did the zebra and the squirrel and the striped mouse get their stripes?

A. There are several reasons that scientists have given over the decades.
A) the stripes allow them to merge into the woodland background, so as to escape predators.
B) Stripes help in cooling the body from overheating.
C) Hunters find moving striped objects difficult to target accurately – the so called "motion dazzle confusion effect."

However this current theory has the most support: that parasites – mosquitoes and flies – find it impossible to attack striped animals, while they can feast on uniformly coloured animals. Dr Tim Caro of the University of California Davis, and Dr Susanne Akesson from Lund University, Sweden, point out that horse flies and similar parasites, which feed on the blood of animals, are attracted to light that is oriented in a particular direction (polarisation) or glare. This glare attracts and helps these insects zone in on the target. Dark skin polarises light better than brown or white. But if the skin were striped dark and white, it becomes less attractive to the bloodsucker bugs. Akesson has argued that the black and white pattern "is ideal in its functions of disrupting this signal of reflected polarized light" and, in effect, is camouflaged to flies as well as big cats." (A science writer, who covered this research paper, has suggested that we use Zebra striped wall paper to shoo away mosquitoes and flies, worth trying!)

Dr Caro and colleagues studied in detail seven different members of the equid family across Africa and Asi), on one hand, studying their skin colouration and striping, and the location and prevalence of blood-sucking flies such as the horsefly and the tsetse across this broad region of Sub-Saharan Africa on the other. Their paper, "The function of zebra stripes," which appeared in the journal Nature Communications finds the strongest connection between the biting fly annoyance and the number, spacing and intensity of stripes in the face, neck, belly, rump, flank and legs of the striped equids.

In effect then, stripes evolved in African equids largely to protect them from the blood sucker insects which abound and thrive in the African tropics. Stripes fool these bugs, perhaps by the disruption of the polarisation of light falling on the striped pattern on the hair and skin. Is this why zebras or striped squirrels are not found in the US, Northern Europe or Russia? Neither is the climate there welcome to such bloodsucker insects.

What is the lifespan of a mosquito?

Adult mosquitoes' lifespans vary from a few days to several months, depending on the species. Some mosquitoes live only in the summer and die when cold weather comes, but their eggs survive the winter and hatch in spring. Others hibernate during the winter as adults, so their lifespan as full-grown mosquitoes last for months, continuing into the following year.

Mosquitoes that spend the winter as eggs develop into adults within two weeks after hatching in the spring. The adult males survive on nectar and similar foods, since they don't need the nutrition that comes from blood, like females do. The males live only about a week, long enough to swarm and mate with the females. The females' lifespan is longer, up to a month or two, though many die sooner, eaten by predators, blown around by storms or slapped when they're trying to get a drink of blood to help them develop their eggs. In nature, birds, dragonflies and spiders eat them.

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