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  • Writer's pictureAndy Hemmer

Diatomaceous Earth for Caterpillars

Updated: 21 hours ago


caterpillar on a flower bud

Diatomaceous earth (DE) is a natural substance commonly used in gardens and homes as an insecticide. Made from the fossilized remains of tiny aquatic organisms called diatoms, DE is primarily composed of silica. It's celebrated for its ability to deter and kill pests by desiccation, essentially drying them out through abrasion. However, there's a common misconception that DE is harmful to all insects, including caterpillars. In this blog post, we'll explore how DE interacts with caterpillars and dispel the myth that it is harmful to them.



 

What is Diatomaceous Earth?


bowl of diatomaceous earth

Diatomaceous earth is a fine powder, derived from the shells of diatoms, that feels slightly abrasive to the touch. When observed under a microscope, it reveals sharp, tiny edges. These edges are effective at puncturing the exoskeletons of small insects like ants, bed bugs, and fleas, leading to their dehydration and eventual death. DE is often used in organic gardening because it doesn't contain harmful chemicals and is safe for use around pets and humans. Be sure to check out our what is diatomaceous earth page!



 

How Diatomaceous Earth Works


For many insects, DE acts as a physical, rather than a chemical, insecticide. The microscopic sharp edges of DE particles cut through the waxy outer layer of an insect's exoskeleton. This waxy layer is crucial for retaining moisture. Without it, the insect loses moisture rapidly and dies of dehydration. This method of pest control is particularly effective for insects with hard exoskeletons, such as beetles, cockroaches, and bed bugs. DE is best applied during dry conditions and when you have a few days stretch of no rain. Be sure to check out our how to use diatomaceous earth for pests page!



 

Diatomaceous Earth and Caterpillars


Caterpillars, the larval stage of butterflies and moths, have soft, flexible bodies covered in tiny hairs. Unlike insects with hard exoskeletons, caterpillars do not have a rigid structure that can be easily penetrated by DE. Here's why diatomaceous earth for caterpillars is less effective, and often harmless, to caterpillars:


Soft Bodies: Caterpillars' soft and flexible bodies make it difficult for DE to cause the same level of damage as it does to hard-shelled insects. The abrasive particles of DE are not as effective against the soft, pliable skin of caterpillars.


Behavioral Patterns: Caterpillars primarily feed on plant leaves and do not typically come into direct contact with DE on the soil or surfaces. This reduces their exposure to DE and its potential effects.


Limited Dehydration: While DE can dehydrate insects with exoskeletons, the soft-bodied nature of caterpillars means they retain moisture differently. Their bodies are less susceptible to the desiccating effects of DE compared to insects with hard shells.



 

What Does Kill and Repel Caterpillars in the Garden?


fuzzy caterpillar on a leaf

If you're dealing with a caterpillar infestation in your garden, there are several effective methods to manage and repel them without causing harm to beneficial insects and plants.


1. Natural Predators

Encouraging natural predators is one of the most effective ways to control caterpillar populations. Birds, wasps, and certain beetles are natural enemies of caterpillars. By creating a garden environment that attracts these predators, you can naturally reduce caterpillar numbers.


  • Birdhouses and feeders can attract insectivorous birds.

  • Planting nectar-rich flowers can attract predatory wasps and beneficial insects.


2. Bacillus thuringiensis (Bt)

Bacillus thuringiensis is a naturally occurring soil bacterium that produces toxins harmful to caterpillars. When caterpillars ingest Bt, the toxin disrupts their digestive systems, leading to their death. Bt is specific to caterpillars and does not harm other beneficial insects, making it a targeted and environmentally friendly solution. Check out our friends at Arbico Organics to get your BT today!


  • Application: Bt can be applied as a spray on the leaves of plants that caterpillars are feeding on.


3. Neem Oil

Neem oil, derived from the neem tree, is an effective organic pesticide that can repel and kill caterpillars. It works by disrupting the feeding and growth of insects. Arbico Organics has Neem Oil here!


  • Application: Mix neem oil with water and a few drops of dish soap, then spray it on affected plants.


4. Handpicking

For small gardens or mild infestations, handpicking caterpillars can be an effective method. Wearing gloves, you can remove caterpillars from plants and relocate them or dispose of them.


5. Companion Planting

Certain plants can repel caterpillars and other pests. For example, planting herbs like dill, fennel, and lavender can deter caterpillars while attracting beneficial insects that prey on them.


6. Physical Barriers

Using physical barriers such as row covers or netting can prevent caterpillars from reaching your plants. Ensure the barriers are secured and do not trap beneficial insects inside.



 

Using Diatomaceous Earth in the Garden


diatomaceous earth on garden soil and plants

While DE is an excellent tool for managing pest populations in your garden, it should be used with caution and consideration for the types of insects you are targeting. Here are some tips for effectively using DE:


  • Target Specific Areas: Apply DE in areas where you have noticed infestations of hard-bodied pests. Avoid spreading it indiscriminately, as it can affect beneficial insects.

  • Protect Pollinators: Be mindful of where you apply DE to avoid harming pollinators like bees and butterflies. Caterpillars often turn into these important pollinators.

  • Reapply After Rain: DE loses its effectiveness when wet, so reapply it after rain or watering your garden.



 

Diatomaceous earth is a valuable tool in the fight against garden pests, but it is important to understand its limitations. Contrary to popular belief, DE does not harm caterpillars significantly due to their soft bodies and feeding habits. By using DE strategically and understanding its impact, you can maintain a healthy and balanced garden ecosystem, protecting your plants from harmful pests while ensuring the safety of beneficial insects like caterpillars and pollinators.


For effective caterpillar management, consider using natural predators, Bt, neem oil, handpicking, companion planting, and physical barriers. These methods are environmentally friendly and help maintain the biodiversity of your garden. Remember, the key to a thriving garden is balance. Use natural remedies wisely, and your garden will flourish with a diverse and vibrant array of life.

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