Eurosta solidaginis
Copyright, Dr. Warren Abrahamson and Paul Heinrich
The Goldenrod Gall Fly is
a parasite
on goldenrod plants. The fly's entire life, and death, is
centered around Goldenrod. This small brown fly is
about five millimeters long. Males are slightly smaller than
females. Females are easily identified by their
ovipositor
(egg-laying tube) extending from their abdomen. Adult gall flies do not
fly well, so they do most of their travelling by walking up
and down goldenrods. The male will choose a bud
on the plant and wait until a female shows up. When a female
approaches, the male does a sort of "dance" to attract
her. After the flies mate, the
female leaves to find a suitable spot on the goldenrod to
lay eggs. To lay them, she injects her ovipositor into the
goldenrod stem. Adult Goldenrod Gall Flies only live about
two weeks. Fly
larvae
will hatch from the eggs in about 10 days. The
larvae will immediately begin to eat from inside
the stem of the goldenrod. The saliva
of the larvae has a chemical in it which causes the
plant to grow abnormally, creating a ball-shaped
"gall"
that the larvae live in. The larvae will
stay in their galls for a full year before becoming
adults.
First, they will continue to eat from within,
making the gall grow larger, until it is the size
of a golf ball. When Fall approaches, the goldenrod
stem and gall will turn brown and each larva will
dig an escape tunnel to leave its gall, but will
not use it until Spring. To prepare for Winter in
the gall, the larvae will produce a chemical in
their bodies which is similar to anti-freeze. It
will keep them from dying from cold
weather. In the Spring,
each larva will become a pupa
(resting stage) before hatching into an adult. The
adult will leave the gall and look for a mate.
Adult Goldenrod Gall Flies do not eat. Copyright, Dr.
Warren Abrahamson and Paul Heinrich Copyright, Dr. Warren
Abrahamson and Paul Heinrich Goldenrod Gall Flies have
many predators,
some even when they are in the larval stage in their gall.
The gall is like protective armor against most predators,
but some locate galls knowing there is a juicy snack inside.
Downy Woodpeckers and Carolina Chickadees are two birds who
seek out galls and break them to get the larvae
out. There is a beetle
(Mordellistena unicolor-no common name) which burrows
into the gall and eats the larva. See a picture of this
beetle below.
Copyright, Dr. Warren Abrahamson and Paul Heinrich
