Critter of the Week: Installment 3

Written by Lee Anne Hanke

Dear all,

Below is Critter of the Week, installment 3.

Take care,



Dedicated to the thousands of non-human neighbors who share our campus with us.  Brought to you by Science at St. Andrews.

Could you imagine, in an average 79-year human lifespan, if you had only 2 years of childhood, followed by 75 years of sleeping (95% of your life), followed by 2 years of adulthood?  No?  This week’s critter of the week does that kind of thing, but all in one year—It is a tiny fly that starts out as an egg near the tip of a Japanese Wisteria (Wisteria floribunda) leaf.  Once it hatches, it burrows into the leaf, feeding inside it—as if the top surface of the leaf was the ceiling and the bottom was the floor of a house, and it eats its way through the “rooms”—this is called leaf mining.  It takes less than two weeks to eat and grow (the mine gets wider as it grows), then it gets ready go into the next phase of its life, the puparium (like a chrysalis), in which it slowly transforms into an adult.  Once it pupates, it mostly sits there in the leaf litter for almost a year.  Then the following March-April, the adult emerges and has only a little time to mate and lay eggs–kind of a grind of an existence. This fly is also a bit of a mystery.  It is only known to eat Japanese Wisteria, but no one has found it in Japan. In fact, so far, the only place it has ever been found is here on the St. Andrews campus.  It is quite probably a new species—we’ll find out hopefully within the year for sure—it was discovered here.  Because of its weird life cycle, and because it is not so common, it has taken a while (5 years) to raise an adult successfully.  So what did it eat before Japanese Wisteria was introduced from Japan?  Many plant-eating insects are pretty picky eaters, because different plants have different poisons. It does not seem to feed on the native Wisteria growing on campus. Did it come from Japan?  The plant this fly eats is all over the place here—Japanese Wisteria is an invasive species, meaning that it takes over places where it grows and grows out of control, keeping native plants around it from growing successfully.  Japanese Wisteria has been introduced throughout the eastern US, and its leaves are available from April to October—so is this fly really only found here?  Why is it active only in early spring, for such a short time?  Perhaps I’ll be able to let you know in a future installment… for now, time to get some sleep!