Why knowing your clothes moths is important

Case-making clothes moth larva on wool.  Courtesy Clemson University. 
USDA Cooperative Extension Slide Series, Bugwood.org

The clothes moth is a common pest of woolens, furs and feathers worldwide.  In the U.S. there are two main pest species: the webbing clothes moth (Tineola bisselliella) and the case-making clothes moth (Tinea pellionella).  These two moths illustrate the importance to an IPM program of accurately identifying pests.

Clothes moths can be an especially important problem in museums and other accounts with a low tolerance for pests.  Fortunately, pheromone traps are now available for use as effective monitoring tools for detecting clothes moths at low population densities. According to Pat Kelley with Insects Limited, Inc., two different pheromone blends are used to attract the two species. While the case-making clothes moth can be attracted to webbing clothes moth pheromone lures due to a shared chemical component of their pheromone, at close range the webbing clothes moth pheromone is partly repellent to the case-making clothes moth.

Case-making clothes moth pupae dangling from
pupation site.  Photo by Pat Kelley.

To use clothes moth pheromone traps effectively, therefore, it's critical to understand the existence of the two types and to learn how to identify them.  Fortunately, distinguishing the two species is not too difficult with either adults or larvae. On damaged articles, the larvae and pupae are relatively easy to distinguish because the case-making clothes moth carries a silken, tube-like case throughout its development.  The webbing clothes moth larva does not carry a case and you will not see a case-making clothes moth feeding "naked"--without its case. According to Kelley, damaged spots on clothes attacked by the webbing clothes moth are characterized by copious amounts of silk webbing or tubes, usually with large amounts of frass (droppings).  The webbing clothes moth is sometimes misidentified as case-making clothes moth because it also spins a silken cocoon once it reaches its pupal life stage.  The webbing clothes moth pupal case, however, is usually attached to the damaged fabric.  The case-making clothes moth tends to dangle its pupal case from a horizontal surface, like a shelf or ceiling, above its food source (see image). 

Clothes moth on a glue trap.  Note the tuft of hair and straight,
downward-pointing palps (mouthparts) with lateral bristles. 
These are two key characters of both species of clothes moth.

Clothes moth adults are small, 5 to 7 mm-long, with brown or copper-colored wings.  Under magnification they are identified by a bristly, rock star-like mop of hair between the eyes and antennae, and by their straight, bristled palps (which are strongly curved in many grain-infesting moths).  Unlike many stored grain moths, clothes moths are shy and not commonly seen flying during the day.  Adult webbing clothes moth are more golden in color, with the tuft of scales between the eyes coppery-colored, and with no markings on the wings. Adult case-making clothes moth are duller in color (brown to gray) and may have a central, dark spot on each forewing. The tuft of hair is also duller (gray to brownish) in color.

Another significant difference between the two species involves how they move and enter traps. Because the case-making clothes moth flies more frequently, Insects Limited recommends a wing (hanging) trap for this species.  The webbing clothes moth prefers running over flight, so traps should be placed on the floor or other flat surface.

All this is important on a practical level because of cost.  Pheromone traps aren't cheap.  The Insect Limited folks currently are the only ones to sell case-making clothes moth traps, which cost approximately $90 for a set of 10.  Trece, sells webbing clothes moth traps with 5-6 lures (depending on whether you choose wing or stick-on traps) for a little over $20 (minimum order of $250).  When conducting surveillance for both species, you'll ideally need both pheromone lures and two trap designs--though Kelley says that webbing clothes moth will fly to enter the wing trap and vice versa.  If you can only deploy one type of trap, buy the one for webbing clothes moth (webbing clothes moth is not attracted to case-making clothes moth pheromone).

The subtle differences between these two species illustrates beautifully both the complexity of biology and the importance of being knowledgeable about your adversaries in an IPM program.