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Caterpillars on ornamental plants

Quick Facts

  • Caterpillars feed on a wide variety of trees, shrubs, perennials and annuals.
  • In most cases, ornamental plants tolerate caterpillar feeding and treatment is unnecessary for plant health.
  • If management is necessary, there are several effective non-chemical and low-risk insecticide options.

How to identify caterpillars

Caterpillars turn into moths and butterflies. They can be very different in appearance.

  • Fully grown larvae range in size from ½ to 4 inches (13-102mm ) in length. 
  • Larvae range in color from pink, brown, green and blue to black.
  • Many have spots or stripes. 
  • Some caterpillars are smooth with few hairs while others are hairy and others have spines on their bodies.
caterpillars have five or fewer prolegs
Caterpillars have five or fewer prolegs.

Don’t confuse caterpillars with sawflies as they can look similar. The best way to tell the difference between them is to count the number of prolegs. 

Prolegs are fleshy false “legs” that are present in both caterpillars and sawflies. Prolegs disappear when the larvae turn into adults. 

  • Moth and butterfly caterpillars have two or five (rarely three) pairs of prolegs.
  • Sawflies have six to ten pairs of prolegs.

Distinguishing between these two groups of insects is important because management differs depending on which is present.

Biology of caterpillars

  • Most moth and butterflies species spend the winter either as eggs or as pupae (a few species survive as adults). 
  • Many are active in the spring.

The time when this first occurs depends on how far north they are in Minnesota and whether we are experiencing a normal spring or an early or late one. 

  • Some caterpillars are not active until summer and can feed into the fall. 
  • Most caterpillars feed individually on leaves, although some feed in non-social groups.
  • Collectively, caterpillars eat many different deciduous trees, shrubs and herbaceous plants.
  • A few caterpillars in Minnesota feed on evergreen trees or shrubs.

Injury caused by caterpillars

Healthy, well-established ornamental plants can usually tolerate caterpillar feeding.

  • Most caterpillar feeding only affects the plant's appearance.
    • There are a few exceptions, such as spruce budworm defoliation on spruce and balsam fir.
  • Young and unhealthy, stressed plants are less able to tolerate feeding. 
  • Severe feeding (e.g. for one to three consecutive years) may slow down plant growth, but plants usually are not killed.

Caterpillars can cause different patterns of damage to leaves. Sometimes different stages of the same caterpillar can create different types of damage.

  • General feeding: eating entire sections, even entire leaves.  
  • Skeletonizing: feeding between the main veins of leaves.    
  • Windowpane feeding: feeding on one layer of leaf tissue between the veins. The damage is translucent (semitransparent) before eventually turning brown.
Caterpillar feeding on tree
General caterpillar feeding on tree
Skeletonizing on leaves caused by caterpillar feeding
Caterpillar leaf skeletonizing on tree
Caterpillar window feeding
Windowpane caterpillar feeding on tree

How to protect plants from caterpillars

Caterpillar feeding, as well as the presence of any webs, is usually just a cosmetic problem, only affecting plant appearance. 

  • Keep plants healthy, a healthy plant can more easily tolerate caterpillar feeding.
  • Select plants that are hardy for your area and plant them in sites that encourage growth.
  • Maintain plant health through proper cultural care, including watering and fertilizing. For information on tree and shrub selection and proper care, see Trees and Shrubs.

How much damage have the caterpillars caused?

  • Ideally, caterpillars are best treated when damage is minor and before feeding becomes extensive. 
  • Once defoliation is severe, treating plants does not help protect them.

How large are the caterpillars?

  • Treatment is most effective when caterpillars are small, no larger than half their full-grown size. 
  • Small caterpillars are easier to kill.    
  • Treating large caterpillars does not prevent feeding damage.

Management options

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Non-web building caterpillars on trees and shrubs

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Web building caterpillars on trees and shrubs

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Large, showy caterpillars

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Caterpillars on perennials and annuals

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Learning about caterpillars

There are many species of caterpillars not included with this information. If you are interested to identify and learn about other species or would like to look up more information about the species discussed here, the following are a few of the many resources available.

 

Jeff Hahn, Extension entomologist

Reviewed in 2020

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