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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.        
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,                  
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.                                           
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      
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        
Deer flies     Wooded and marsh areas                       
General Articles                                            

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