Eliminating Spanworms: A Comprehensive Guide to Controlling This Garden Pest

Understanding Spanworms

Spanworms, or inchworms as they are sometimes called, are the larvae of certain moths. They get their name from their unique way of moving, which looks like they’re “spanning” or “measuring” the surface they’re on. These pests are a common problem in gardens, feeding on a wide variety of plants and causing extensive damage if left unchecked.

Identifying Spanworms

It’s essential to properly identify spanworms to apply appropriate control measures. These larvae are typically green, brown, or grey, making them well-camouflaged with the plants they feed on. They have a slender body and move with a distinctive looping motion, which sets them apart from other caterpillars.

Damage Signs

Spanworms chew irregular holes in the leaves of plants, often leaving the veins untouched. Their feeding can lead to defoliation, reducing the plant’s ability to photosynthesize and causing significant harm to its growth and productivity.

Natural Predators of Spanworms

One of the best ways to control spanworms naturally is to encourage their natural predators. Birds, predatory beetles, and parasitic wasps are among the creatures that feed on spanworms. These predators can be attracted to the garden through plant diversity, providing shelter, and avoiding broad-spectrum insecticides that might harm beneficial organisms.


Birds are particularly efficient in hunting spanworms. Providing nesting sites, feeders, and water sources can make the garden more attractive to birds.

Predatory Beetles

Certain beetles, like ladybugs, actively prey on spanworms. Planting flowers that attract these beetles can be a vital part of spanworm control.

Parasitic Wasps

Parasitic wasps lay their eggs inside spanworms, and the emerging larvae consume the host. Encouraging these wasps can be an excellent biological control strategy.

Cultural Practices for Spanworm Control

Altering gardening practices can be an effective way to minimize spanworm damage. These methods are generally non-toxic and can be used in conjunction with other control strategies.

Regular Monitoring

Checking plants regularly for the presence of spanworms or their damage allows for early detection and intervention.


If the infestation is limited, handpicking spanworms from the plants and disposing of them can be an efficient way to reduce their population.

Proper Watering and Fertilization

Avoiding excessive watering and fertilization can make plants less attractive to spanworms. Healthy plants are often more resistant to pest damage.

Chemical Control of Spanworms

In cases of severe infestation, chemical control might be necessary. Choosing the right product and following the manufacturer’s instructions is vital to control spanworms without harming other organisms.

Insecticidal Soaps and Oils

These can be used to kill spanworms on contact. They are often considered less harmful to non-target organisms.

Synthetic Insecticides

Some synthetic insecticides can effectively control spanworms. Care must be taken to choose a product that is appropriate for the specific situation and to follow all safety guidelines.

Biological Control with Bt (Bacillus thuringiensis)

Bt is a soil-dwelling bacterium that produces toxins specific to certain insects, including spanworms. Applying Bt as per instructions can be an effective way to control spanworms without harming other insects.

Prevention and Future Management

Preventing spanworm infestations is often more manageable and cost-effective than trying to eliminate an established problem. Planting resistant varieties, rotating crops, maintaining garden hygiene, and fostering a garden ecosystem that supports natural predators can all contribute to keeping spanworm populations in check. Regular monitoring, proper identification, and an integrated approach using cultural, biological, and chemical control methods can help manage spanworms in the garden effectively. By understanding the biology, behavior, and available control measures, gardeners can keep spanworms at bay and maintain healthy, thriving plants.