Beware - The Dirt Worms are Back! Tom Ellis, Entomology
We've had a rash of calls from various points around the
mitten regarding little bits of dirt or sand that seem to
be eating various kinds of foliage. Folks are surprised to
learn that these dirt worms are insects. They are even
more surprised to learn that they are in the moth and
butterfly taxonomic order Lepidoptera.
The snailcase bagworm, Apterona helix, was first introduced
into the United States from Europe around 1940. Since it
resembles a small clod of dirt, the bagworm can go
unnoticed for many years. Initial reports usually come
from homeowners who collect them from house siding,
automobiles, trees, or fence posts. They are very
difficult to remove from these surfaces.
The snailcase bagworm has the potential to become a serious
pest for several reasons: 1) the insect feeds on many
different types of plants, 2) it is parthenogenic (i.e.,
the female reproduces -males not known for this species)
without being fertilized, and 3) the insect easily can be
carried long distances by mammals, birds, or humans.
Damage
Larvae feed on plant tissues and mine circular areas
beneath the surface layer. Large numbers of bagworms
contaminate crops by attaching themselves to the plant
surface. In Washington, the bagworm is a nursery pest,
especially on baby's breath. The bagworm attaches its case
so tightly to houses and cars that you may remove the paint
in order to dislodge them.
Description and life cycle
The snailcase bagworm is a member of the moth family
Psychidae (SY-KA-DAY), the bagworms. Each larvae produces
a protective bag by cementing small particles of soil into
place. It lives inside this bag for virtually its entire
life cycle. As the larva feeds, it enlarges the bag until
it measures about 1/4" across. The bag resembles a coiled
snail shell, ergo its moniker. From a distance of more
than a couple of feet the bagworm cases look like little
dirt clods.
The snailcase bagworm overwinters as a partially grown
larva. I would hazard a guess that our recent mild winters
have enhanced their survival. Feeding begins in the
spring, probably as soon as sufficient greenery appears.
After completing larval development, these insects may
cluster in protected areas at the base of trees, or around
house foundations, where they form pupae. In central and
eastern Washington, this occurs in May and June. This year
that seems to be happening in Michigan right now. Keep in
mind how far behind we are here this year,
weather-wise.
The adult female emerges in a couple of weeks. Psychidae
are in a general group of moths called microlepidoptera
(the moths are tiny). However, the adult female snailcase
bagworm looks more like an amorphous sack than your typical
garden variety mini-miller. The female stays inside the
protective case (bag) to lay eggs (don't forget she doesn't
mate). Eggs hatch in about two weeks. The baby larvae
just kind of hang out in the bag (snailcase) until the
following spring.
Hosts
Almost anything green. Dan Suomi from Washington State
University reports that these critters feed on at least 100
different species of plants. I'll list a few to give you
an idea of the range of their appetite: alfalfa, apple,
baby's breath, bean, broccoli, cabbage, Douglas-fir,
marigold, quackgrass, radish, rose, tomato, and violet. It
is also presumed that they will also feed on algae and
fungi.
Distribution
In Washington, the snailcase bagworm was historically
restricted to dry rangelands. Recently it has been moving
into more moist and hospitable valleys.
There seems to be no real pattern of distribution of the
snailcase bagworm in Michigan. Last year, most of the
observations that made their way to our office came from
Flint, Oakland County, Muskegon, and Big Rapids. This year
we've had calls from as far north as Gaylord and Chalevoix.
Integrated snailcase bagworm control
Our current knowledge of natural enemies of the snailcase
bagworm---zip, zed, nada.
The Washington State Extension folks advise that various
insecticides will give good control, but only when the
larvae are actively feeding. Spraying after they cease
feeding for the year is not effective because of their
protective dirt bag.
Washington State advises the use of B.t., diazinon or
carbaryl to control the bagworm on crops grown for human
consumption. In addition, acephate can be applied to sites
such as ornamental trees and shrubs. To avoid killing
pollinators, do not apply an insecticide (except B.t.) to
plants that are flowering. Be sure the crop is on the
label of any insecticide you may choose to apply. Read the
pesticide label and use only as directed.
New Bugs on the Screen - Two-week forecast
Tom Ellis, Entomology
What Where
Armyworm Side of house
Mosquito Everywhere
Larder beetles Basement
Black flies Within 5 miles of clean, cool flowing
streams
Deer flies Wooded and marsh areas
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This file was generated from data base C1 on 05/15/97. For more information about this
data base or its contents please contact landisj@msue.msu.edu
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