Will Insecticidal Soap Kill Caterpillars

Insecticidal soaps are one of the most non-toxic pesticides available which folks lean towards in order to kill bugs while protecting plants.  The thing is a lot of people use it incorrectly, or for the wrong types of bugs, caterpillars being one of them.  It is more useful in killing small, soft-bodied bugs and their larvae such as spider mites, mealy bugs, aphids but not the larger, chewing bugs… like caterpillars.

Insecticide soap is a true soap that is made by way of combining potassium hydroxide with long-chain fatty acids, which, of course, are all made from fat.  The ingredients are such that they do the damage to the bugs, but they are perfectly safe for people, plants, and everything around them.  

Soap needs moisture to be effective.  This is another common mistake.  Folks let it get dry.  Once it is dry, it is completely ineffective. Dry soap will decompose very quickly into harmless compounds. You have to keep it wet to keep the effect.

Any insect has to be completely saturated by the spray.  The fatty acids start to act and disrupt the insect’s cells’ membranes that begin to ‘leak’, basically dehydrating the bug until it dies.  You’ll want to repeat this every four to seven days as is needed until they are all gone.

Before you begin to use any spray at all on your plants consistently, you want to make double sure they’re not harmful.  Choose a small part of the plant and spray just a minimal amount as a test spot.  You should wait twenty-four hours to see if there are any negative effects, e.g. any kind of spotting or wrinkling of the leaves, or any browning.  If so, discontinue.  Some soap sprays are not good for certain ferns or gardenias.

​It is recommended that you apply every four to seven days, or as needed.  The fatty acids are going to dry the bugs up fairly quickly.  After they’re gone, you want to wash your plants’ leaves really well in order to get rid of the soap.  It’s not going to hurt them, but it’s a good idea to get rid of any unnecessary substances on a plant’s leaves.

​A caterpillar is considered a chewing insect, and they eat extremely quickly and a lot! They mostly eat the leaves of plants, some larvae and eggs of other insects, but for the most part, they are herbivores.  It is a very elongated, worm-like larva that will become either a butterfly or a moth.  They continue to eat leaves on a variety of plants and trees to the point that they can cause extensive damage or even destroy it completely before they become a pollinator.

There are some species, e.g. the cabbage looper moth’s larvae for example, that can consume upwards of three times of its body weight each and every day and their feces can stain the remaining leaves. So, if you’re not careful, that’s your cabbage patch eaten and ruined in no time at all. Other caterpillars don’t have specific tastes for any particular leaf; they’ll just feast on any that they come across.

They do have natural predators in birds, ladybirds/bugs, and yellow jacket wasps. They also have such a high nutritional value that in some parts of the world, humans eat them as a delicacy. (Not kidding).  Caterpillars contain more protein and fat than beef, lentils and fish.

There are a lot of natural repellents that you can use to prevent caterpillars from ever coming to your garden to begin with.  If you plant strong smelling companion plants, this will discourage them.  You can even use them inside as a friend for your indoor plant.  They don’t like strong smells, so plant these herbs beside your outside and inside plants:

• Peppermint
• Lavender
• Mugwort
• Sage

These not only will deter caterpillars, other pests will steer clear as well.

• Garlic.  This is a naturally acidic substance that is known to kill as well as repel caterpillars.  They don’t like it.  Get a spray bottle and put two cups of water mixed with two spoons of garlic powder and spray away.  Naturally harmless to everything except these little critters.
• Bacillus Thuringiensis.  Treat your plants with this.  It affects only caterpillars and will kill them.  It is a bacterial disease as well as a biological control.  It is particularly effective when it is used against really small caterpillars that have just recently hatched from their eggs.   You can find it under the name Thuricide, Dipel and a few other names.  You use it by dusting it over the plant leaves or you can also spray it in solution.  You need to read the label and follow the instructions carefully to get the dosage exact.

You need to make sure to coat the plants completely so that the caterpillars ingest the stuff while they’re eating.  This is an organic solution perfectly safe for pets, people, plants, everything except the bugs.  You should use it every three to five days until they are gone.

• Spinosad.  This is an insect spray that is made from a bacterium that is commonly found in soil.  It is similar to Bacillus Thuringiensis.  You will be able to find it in a number of different organic insecticide solutions.
• Soap/water solution.  The infamous insecticide soap.  Here folks hand pick the caterpillars and their eggs from plants and then throw them in a bucket of the substance to drown them.  This is a pretty awful way to kill a living thing. If you’re going to kill something, it needs to be done in as quick, painless and humane way as possible. Drowning them does not do this.

You also want to do some research before you begin your elimination process, and see what species are munching through your garden, which ones will turn into butterflies, which ones will turn into moths, which butterflies are endangered and which butterflies are beneficial to the ecosystem.  Do some homework as to how you can transplant the ‘good’ ones without losing your plants.

It’s actually kind of ironic in a sense because butterflies are pollinators and they help plants in so many beneficial ways.  In order to get to the butterfly stage, their larvae have to eat plants aggressively in order to turn into the creature that is going to pollinate and help those same plants.  It’s kind of wild; we’re killing the critters that actually help our plants continue to thrive and expand from one space to another.

By eliminating the butterflies – thus preventing them doing their job – our actions can drastically decrease a plant’s numbers, so, in a roundabout way, our insecticide practices can and do affect other animals and thus us. The whole ecosystem can be affected because of our war on caterpillars.

Understand the type of insect you are targeting, the species, what it is going to become when it reaches maturity, what its purpose is in the ecosystem, its benefits. Do you really need to kill them?

1. Never treat flowering plants for any reason.  You will run the risk of harming pollinators, which will in turn risk harming the plant species as a whole. Check the impact this has had on bee numbers, for example.
2. Don’t spray in areas where pollinators are actively working, such as where you find butterflies, bees and moths.
3. Whenever possible remove the weeds in your yard by actively mowing or pulling them out as opposed to using any type of chemicals in order to get rid of them.
4. If you absolutely must use insecticides during a flowering period in order to save a crop try to use sprays that decompose quickly and that are residual, as well as having low-hazard formulations. Only spray at this time if there is no other choice and it is an absolute necessity.
5. Be sure to put the insecticides onto the plants when the pollinators have stopped foraging for the day, e.g. in the evening or in the very early morning.
6. Adjust your spraying programs in correlation to the weather conditions outside, e.g. if it is windy out, do not spray.  It will travel and get on things that you don’t want it to.
7. Always read any labels, follow the warnings and the instructions exactly.  Make sure you understand what chemicals and substances are included in the product.
8. You may not want to but, when possible, remove the bugs by hand.  This is especially effective with caterpillars.  Just carry them to where they aren’t going to annoy you, or where they will be beneficial.
9. Reduce spray nozzle pressure so as to prevent pesticide drift.
10. We all want to have a positive impact on the ecosystem.  Yes, you want to save your plants, but you don’t want to destroy the pollinators in the process: As that can quickly become a win-lose-lose kind of situation.