Butterflies can be recognized by their “powder-covered” (scaled) wings. Butterfly antennae end in small “balls” (clubs). Moths do not have similar appendages. They are part of a family containing a large number of species with very different behaviours (there are even aquatic moths!). Only a few of these species feed on foodstuffs. The most common species that can be found in homes is the Indian-meal moth. When inactive, the moth places its four wings in such a way that only two are visible. The visible wings appear to be striped with a wide pale band, and the wing tips are of a contrasting reddish brown. Since these colours exist on easily-detachable scales, they are harder to observe in an adult in the late stage of its life, especially if its wings were touched by fingers. Other moths found in the home can be greyish or brownish, with a few spots or wavy or zigzag lines. Other kinds of moths, that prefer to feed on clothing, can also be found indoors; these are called clothes moths.
Moths begin their life from an egg laid at night from which a caterpillar emerges. It feeds on food products and leaves a trail of silk behind as it moves. Depending on the species, it might even be covered with a velvety sheath to protect itself while it is feeding. It then weaves itself a cocoon of silk in which it undergoes metamorphosis. At this stage, it is known as a chrysalis and it does not feed. If the insect is not trapped in a container, its cocoon can be found far away from the source of nourishment. The adult or moth emerges from the cocoon and its role is to mate to perpetuate the species.
The caterpillar stage can withstand the coldest temperatures. Some caterpillars will even go into diapause, a resting stage that enables them to await more favourable conditions, and makes them more resistant to fumigation.
In cases of heavy infestations, the surface of the grain or foodstuff may be covered with the tangled threads the caterpillars leave behind as they move about. These threads provide better ambient conditions for the caterpillars and protect them against their natural parasites.
Places where they can be found in the home
The Indian-meal moth will accept an impressive variety of foods (grain, powdered milk, cookies, flour, etc.). It is known to be especially fond of figs and other dried fruits, dried red peppers, nuts or chocolate containing nuts. Some larvae have even been known to attack fresh apples and pears in warehouses.
Avoid leaving dry dog food or bird seed within reach of these insects. Try to find out if squirrels have been hiding nuts somewhere indoors.
Use hermetically sealed plastic or glass containers with a rubber seal to store all foodstuffs. Wash the containers well before putting food in them.
Inspect pantry contents on a regular basis because these insects produce a lot of eggs that can develop over a short period. The Indian-meal moth is also attracted by mouldy foods.
Wipe down shelves often and vacuum them as well.
Inspect the back of bookcases, around ceiling edges, and closet cracks to locate cocoons.
Install screens to prevent moths from entering and plug up cracks so that they cannot serve as shelters for cocoons or crumbs (in the pantry).
Upon seeing one of these moths, you must first find the infestation site or sites. Usually, it will be a bag that hasn’t been used recently. You will find some caterpillars or small silk threads, sometimes mixed in with excrement. If your threshold of tolerance is exceeded, you will be tempted to put the infested foodstuffs in a garbage bag and remove it from your home quickly to get rid of them, but it is better to expose them to extreme temperatures by freezing them for several days or cooking them in the oven to ensure that these insects will no longer be around in the environment. Sometimes, the problem is solved at this stage, but you will have to be even more vigilant in the days and weeks to come just in case the infestation is not under control. In some cases, food that is only slightly infested can be preserved by exposing it to extreme temperatures. In other cases, such a practice is not recommended because the presence of insects in food promotes the production of dangerous toxins produced by microscopic fungi that would not be destroyed by the heat.
The use of pesticides is never recommended on surfaces near food. You must be well informed to avoid unpleasant incidents. It might be better to use diatomaceous earth. The caterpillars will scratch their outer envelope when they rub against this silicon-based powder, and they will then die of dehydration.
Pheromone traps have proven to be very effective in detecting the presence of this insect (or determining if it is still around). The pheromone is an odoriferous substance emitted by the moth when it wants to mate. Males are attracted and caught in the trap.
For heavy infestations, you can use a variety of insecticides, such as bacteria (BT) that kills the caterpillars, a small insect that attacks the eggs, and products that prevent the young insects from developing properly.
Not all moths seen indoors are clothes moths.
Spontaneous generation does not exist. Insects never appear by magic in poorly-maintained places. Both the larva (or caterpillar) found in a jar of foodstuff and the adult seen flying around the room always come from eggs laid by an adult female. The egg is so small that you would not notice it, and it will not necessarily have been laid in the home in which it is found.
Caterpillars, whether big or small, are always immature insects. Contrary to what many people believe, they all metamorphose into moths (unless they die first).
People often think they are buying insect-free certified products. In fact, in order for an imported cargo to be rejected after a careful inspection of samples, it must not contain more than a certain number of insect parts. The latter could therefore well be found on occasion in our dates, spices, or flour, and this situation would not be unusual.