Most blood-sucking insects urinate
while they feed so they can avoid filling up on fluid and get more nutrients
out of their meal.
But some species of mosquito also do
what is called preurination — they excrete drops of freshly ingested blood
without extracting any of the nourishing blood cells.
The behavior has always confused
scientists because “blood is a very precious resource,” said Claudio R.
Lazzari, an entomologist at François Rabelais University in Tours, France. “The
risk of taking it is very high.”
New research, conducted by Dr.
Lazzari and colleagues and published in the journal Current Biology, shows that
the preurine may serve to keep the cold-blooded mosquitoes from overheating
while they take their blood meal, which can be as warm as 104 degrees
Fahrenheit, depending on the host animal.
Roughly one to two minutes after she
starts feeding, an Anopheles stephensi mosquito will excrete urine and preurine
through the anus, at the end of the abdomen. Sometimes a drop of the fluid will
form and cling to the body before falling off; when this happens, some fluid
evaporates like sweat and cools the mosquito’s abdomen by almost four degrees.
Mosquitoes also feed on nectar, but
they tend not to preurinate when they eat lower-temperature, sugar-based meals.
The mosquito is not the only insect
that uses ingested food to regulate its temperature. Aphids excrete honeydew to
prevent their abdomens from getting too hot, and some bee species regurgitate a
bit of nectar to keep their heads cool while they fly.
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