You go to make your child hot cereal for breakfast and a moth flies out of the box. You quickly hatch Plan B before the school bus arrives.
Indian meal moths are the most common of these so-called "pantry pests."1 As adult moths they are harmless, other than to your sensibilities as a good housekeeper and parent. But the larvae are the culprits when it comes to eating and contaminating stored foods in the cupboard.
Having a few moths in your pantry may not be the end of the world, but it can be unnerving to find something you are about to eat full of worms and grit, especially with kids to be fed before school or guests about to arrive. The good news is that with a bit of effort, this nuisance can be eliminated.
Description And Life Cycle
Adult Indian meal moths (Plodia interpunctella) are about one half-inch in length and have distinctive bi-colored wings. The part of the wing closer to the head is tan or a light gray, while the other section is a darker brown or copper color.2 The adult moths only live for about a week, long enough to mate and for female moths to lay eggs on food items.3 In a few days, whitish caterpillars with brown heads hatch 4 and may feed in your cupboard for several weeks or months, depending on the temperature.3 When they are ready to pupate, the caterpillars will often wander away from the foodstuff to spin a loose cocoon in some corner where they may spend up to several weeks before emerging as adult moths.3 In warm weather, the entire life cycle takes six to eight weeks,4 but it can take up to six months under cooler conditions.2
Indian meal moth caterpillars have eclectic tastes and eat a wide range of foods. Commonly infested foods include: coarsely ground grain (e.g. cornmeal) and cereal products, dried herbs and fruits, nuts, powdered milk, flour, hot pepper flakes, spices, dry pet food, bird seed, and decorative items made with seeds.1,2,3
Detecting An Infestation
Finding webbing in a stored food product is a sign that you have an infestation.1 You may also find small, pale caterpillars. Look a little more closely and you may see a fine gritty material; this is frass, the scientific term for insect poop.3
Another pretty sure sign of an infestation is seeing adult moths fluttering weakly through the kitchen. Though they can sometimes be found throughout the house, more often than not they are where the food is. People sometimes confuse clothes moths with Indian meal moths.4 The wings of clothes moths are always a single color, usually a tan or buff color of some sort, while the Indian meal moth wings are bi-colored, like a '50s Chevy with a two-tone paint job.
The only way to control Indian meal moths is to locate infested materials and them out. A thorough cleaning is also needed to get rid of errant caterpillars, cocoons and food sources. No one recommends spraying insecticides in cupboards or food areas because of the risk of illness from eating contaminated food.
The healthy solution is to take all food items out of the cupboards and going through them one by one. Focus especially on items you bought "in bulk" or that are in open or loosely sealed containers. Inspect each item, looking for webbing and caterpillars. Discard anything that is infested and take the trash out right away. When in doubt, throw it out! Then make sure that you transfer any non-infested food from bags or open boxes into tightly sealable containers.5
The final step is to clean the cupboards thoroughly before putting food back. Vacuum cracks and crevices and wash the shelves. Indian meal moths need remarkably little food to survive so you should also clean behind appliances and anywhere else crumbs and other bits of food may be hiding.2
Packaging - Seal It Tight
It is essential that all food be kept in containers that can be tightly sealed, like a Mason-style glass jar with a screw lid, plastic container with a tight snap-on lid, or a metal container with a tight-fitting lid.3,5 Leaving food in open boxes is just asking for trouble, but a box of cereal that is finished up a week or two should not be a problem.
Hot and Cold Treatments
You might want to rescue infested birdseed or a treasured decorative item. Both freezing and heating will kill Indian meal moth larvae. Effective freezing methods include keeping the contaminated item for four to seven days in the freezer. To eliminate larvae with heat, bake the item for one hour at 140°F or two hours at 120°F in a shallow pan or tray in the oven, or for five minutes in the microwave2. After the hot or cold treatment, be sure to store the seed or item in a tightly sealed container.
Traps for Monitoring
For those of you with scientific inclinations, pheromone traps can be fun, educational, and even useful for determining if you still have a problem. A pheromone is a hormone that attracts males in much the same way that perfume or cologne catches the attention of the opposite sex. A pheromone trap with an Indian meal moth lure attracts the male moth to a piece of glue-covered cardboard where it gets stuck and dies, indicating that you still have moths.4
Re-infestations are always a possibility.
- Refrigerate or freeze small amounts of highly susceptible foods such as spices.5
- Avoid purchasing large quantities of bulk items that are consumed slowly. Susceptible items stored for six months can develop serious infestations.2
- Re-package slowly eaten foods into tightly sealable containers.
- Clean up spills in cupboards and elsewhere promptly.
- If you do see more moths, do a thorough inspection to find the infested food items, including dried pet food. They will be hiding somewhere.
- Cranshaw, W. 2003. Indian meal moth [no. 5.598]. Colorado State University Extension. http://www.ext.colostate.edu/pubs/insect/05598.html
- Lyon, WF. 1997. Indianmeal moth [HYG-2089-97] Ohio State University Extension. http://ohioline.osu.edu/hyg-fact/2000/2089.html
- Antonelli, AL, et al. 1994. Meal moths [EB1396]. Washington State University Extension. http://cru.cahe.wsu.edu/CEPublications/eb1396/eb1396.html
- University of California. Agriculture and Natural Resources 2002/ Pantry pests (Pest Notes: UC ANR Publication 7452.)http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7452.html
- Lewis, D, Hahn, J and P Pellitteri. 1995. Insect pests of stored foods (IC-407). Iowa State University Extension.http://www.extension.umn.edu/distribution/nutrition/DJ1000.html
Stein, Dan. "Indian Meal Moths: a Pantry Pest," NCAP.