The OTHER clothes moths

This week I received reports of two insects that are sometimes confused with clothes moths or pantry pests. The brown house moth, Hofmannophila pseudospretella, is a common moth pest in the United Kingdom, but much less so in the U.S.  In a paper written in the 1950s, one researcher noted that it probably occurred in small numbers in every private home in Britain, and that few stores or warehouses in Britain were without at least a small population.  The brown house moth specimens I saw on a sticky card this week, however, were the first ones of this moth I've ever encountered in Texas.

Brown house moth on sticky card.  Head to tail, these  
small moths are between 4 and 7 mm long. 

The BHM could easily be mistaken for Indian meal moth based on size.  But wing patterns are different.  Wings are bronzy brown with dark flecks on the forewings.  It is a slow grower with about one generation per year, but capable of becoming abundant under the right conditions.  It appears to require high relative humidity of 80% or more, perhaps accounting for the fact that it is not so common in climate controlled homes here in the U.S.

The diet of BHM is varied, ranging from cereal products to wool and dead insects.  It is readily capable of developing in wheat germ, whole wheat, damaged beans, macaroni, fish meal.  When yeasts were present, it could also develop on feathers and flannel wool.

Woodroofe, a British entomologist who studied the moth over 60 years ago, felt that the importance of this moth in homes was more as a fabric pest than a pest of stored grains.  If this moth is found in a home the most likely source of infestation would likely be in a basement or garage with higher humidity.  Check for pet food, woolen clothing, furs or feathers being stored under damp conditions. Also look in light fixtures with dead insect accumulations, or old bird nests in chimneys or soffits. Sticky traps may be useful in catching some of the moths for identification. If the suspected site of infestation is in an inaccessible void, consider dusting the area with Cimexa or Tri-Die, or other dessicant dust. If given a chance, these little moths can become very abundant.

Household casebearer cases collected from a
home in east Texas.  Note the caterpillar head
emerging from the case on the far right, and the
flattened cases widest in the middle. Photo by
Randy Reeves.

Another interesting insect that I encounter more frequently in samples is the plaster bagworm or household casebearer, Phereoeca uterella.  A close cousin to the clothes moth, household casebearers live inside a spindle-shaped silken case.  University of Florida provides a nice article on this moth, which feeds largely on spider webs.  If that sounds like an odd thing to eat, remember that spider webs are a type of proteinaceous silk, and probably just as nourishing to a clothes moth as silk clothing made from silkworm silk.

Like the BHM, household casebearers thrive in higher humidity conditions.  The cases, like a silk purse, are usually flat in later life stages.  It is most likely to be confused with the casemaking clothes moth, a more frequently encountered pest; but the spindle shape, and flattened case are distinctive.  According to the Florida fact sheet these cases may be found "under spiderwebs, in bathrooms, bedrooms and garages... on wool rugs and wool carpets, hanging on curtains, or underneath buildings, hanging from subflooring, joists, sills and foundations; on the exterior of buildings in shaded places, under farm sheds, under lawn furniture, on stored farm machinery and on tree trunks."  Besides spider silk, the caterpillars have been observed to feed on wool, human hair and dead insects.

I've not heard of any infestations severe enough to require insecticide use with household casebearer. In most cases they seem to be a curiosity more than anything; but a vacuum cleaner to get rid of spider webs would be a good idea to make sure that your casebearers don't decide to nosh on something a little more valuable in the home.

Running from Little Brown Moths

Little brown moths, like this meal moth,
Pyralis farinalis, can pose an identification
challenge to untrained PMPs.

Skill at insect identification is one of the little things that distinguishes the well-trained from the not-so-well trained pest control technician. And one of the pest problems that stop many a technician in their tracks is the so-called, "little brown moth".  Even entomologists are disposed to run the other way when a little brown moth shows up--so much so that bug experts often use the acronym LBM when sorting these insects from other, more interesting creatures.

But it's really not fair to the moths, or your customers, to give up so quickly on little brown moth identification--especially when the moth is an indoor pest. Household moths are pretty distinctive when examined carefully, and with a little practice identification decisions about indoor moths are not that difficult to sort out.

First a little background.  Moths, along with butterflies, are insects in the Order Lepidoptera--one of the largest insect groups, with almost 175,000 known species. Perhaps the most distinctive lepidopterous feature is the membranous wing surface covered with flattened, modified hairs, called scales.  Scales are what give each species of moth or butterfly their distinctive body and wing color pattern. 

All Lepidoptera go through a complete metamorphosis as they develop.  This metamorphosis starts out with the egg and larval, or caterpillar stage.  After the caterpillar is fully developed there is a pupal stage, then the adult emerges. In moths, it is typically the caterpillar stage that causes the most damage to plants or to stored products; although in pest control the adult stage flying indoors can also be a problem. 

The most common indoor pantry
pest is the Indian meal moth, shown
here resting in its characteristic
push-up position.

Your first job when faced with an indoor LBM problem is to determine the source. Is the moth coming indoors from outside, or is there an indoor source of the infestation?  And secondly, is this a food-infesting pest, or is it a clothes moth?  The first question can be answered to some extent by considering the numbers of moths present (outdoor moths should not be common indoors), but also by familiarity with the important indoor moth pests.  The second question is answered by familiarity with the appearance and behavior of the two major species of clothes moths.

Comparison of sizes and wing
shapes of Indian meal moth (top),
Angoumois grain moth, and
clothes moth (bottom).

The most common types of moths found in residential or commercial interiors are pyralid moths. Pyralid moths include the Indian meal moth, Mediterranean flour moth, almond moth, raisin moth and others. These moths all have a relatively short fringe of hairs on the hind wing.  The Angoumois grain moth is a smaller moth with a 1/2 inch (13 mm) wingspan and a long fringe of hairs on its hind wings shaped like a pointing finger (see right).

Clothes moths are the smallest of the moths likely to be found indoors (3/8-inch or 5-7 mm wingspan). They are covered with light brown to golden scales and have a tuft of hairs on the forehead. The hind wings lack a pointing finger shape. Clothes moths do not readily fly, and prefer to scuttle or run. For this reason, clothes moths can usually be ruled out as the culprit when a client reports seeing flying moths commonly indoors.

If in doubt as to the source of an indoor moth problem, pheromone lures can help. Pheromone lures contain copies of the sex pheromones that these moths use to locate mates. Pheromone lures can be placed throughout an account to help pinpoint moth hot spots. Some pheromone formulations for moths are even available as confusing agents to prevent males from finding female hosts (this approach is not effective for clothes moths, as explained in an interesting article just out in Fumigants and Pheromones newsletter).  Pheromone traps are available for many species and Insects Limited is an excellent source for information on selection and technical aspects of pheromone use.  Another commercial source for pheromones is Trécé Inc.

For anyone with deeper interests in stored product pest identification, including detailed keys to stored product pests, an excellent resource is the USDA Agriculture Handbook 655, Insect and Mite Pests in Food, now accessible online.

With all the great resources available there really is little reason to run from those Little Brown Moths.

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.