Many little critters in our gardens have cigar shaped bodies and munch on our plants. Most people lump them all together under the term "caterpillar".

Caterpillar - Technically, caterpillars are the immature (larval) stage of either a moth or a butterfly. They are members of the very large insect family, Lepidoptera. The ones that we commonly see in the home landscape are generally foliage eaters that chew on our leaves. The caterpillar has three pairs of legs under its thorax which is the area right behind the head. It has between two and five pairs of prolegs on their abdomen behind the thorax.

The adults are moths and butterflies which have large wings in relation to their body size. They often feed on the nectar in the flowers in our gardens. Why some of these flying insects are called moths and others are butterflies is not clear. Entomologists agree on most of them but there is a gray line between whether some species are butterflies or moths.

Sawfly Larvae - In the garden several insects such as European pine sawfly or Mount Ash sawfly larvae look a lot like caterpillars. One difference is that they do not turn into moths or butterflies. Their adult stage is a type of fly related to wasps and bees. Also, the larvae tend to feed in groups and have no hairs on their bodies.

Why the Difference is Important

Learning the difference between caterpillars and sawfly larvae is important for a couple of reasons:

  1. Pest Identification - Before you try to treat any problem in your landscape, the first step is ALWAYS to properly identify the cause. A lot of pesticides are recklessly put into our environment because people use the wrong control measure on the wrong pest at the wrong time.

  2. Organic Controls - One of the key tools in the arsenal of the organic gardener is a biological control called Bacillus thruingiensis or Bt for short. Apply some of this to foliage being eaten by caterpillars and they get a stomach ache, stop eating and die. The nice thing is that it only has this effect on caterpillars and not on other insects or animals.

    The key here is to remember that it ONLY kills caterpillars, those members of the Lepodoptera Family of insects. Since sawfly larvae do not fall into that category, Bt will NOT work on European sawfly, mountain ash sawfly or any other of their kind.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.


Types of Insects

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