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How to Identify Butterfly Larva

Adult butterflies are some of the most colorful and striking insects in the world, but so too are their larval stages -- caterpillars of diverse shape and patterning. Usually smaller than the equally varied caterpillars of the related moths, butterfly larvae are usually seen feeding as they swiftly gain size, molting off old exoskeletons as they outgrow them. After a number of repetitions of this process -- sometimes appearing strikingly different between molts -- the caterpillar ensconces itself in a chrysalis to undergo the evocative transformation into a winged, mature butterfly. Identifying caterpillars is made much easier with the help of an illustrated butterfly reference, when you can compare photographs or paintings to the tiny, slow-moving, handsomely colored creature you're examining.

Things You'll Need

Butterfly field guide
Plant field guide

Instructions

- 1
  Gauge the caterpillar's size. This is often less diagnostic for caterpillars than for butterflies, as there is a great variability to larva dimensions. It may be a rough guide. The two-tailed swallowtail butterfly's caterpillar, for example, can be more than 2 inches long -- on the large end for butterfly larva. Those of one of the gossamer-winged butterflies will usually be substantially smaller.
- 2
  Consider the caterpillar's coloration and pattern. This, too, can vary within a given species. Many butterfly larva show different color morphs, and their hues and patterns may shift with progressive moltings. But the intricacies of the caterpillar's coat are one of the most important clues to its identification. Take note of banding, spots and stripes -- or uniform, solid coloration, whatever the case may be.
- 3
  Look at the caterpillar's body for distinctive physical features. Some, like the Gulf fritillary, sport spines. Others, like some of the harvester butterfly larvae, may appear almost hairy. Still others may have relatively smooth exoskeletons.
- 4
  Identify the caterpillar's host plant. You will frequently find butterfly larvae on the plants they predominantly feed on and eventually attach their chrysalises to. Monarch caterpillars famously feast on milkweed, though some other caterpillars, including those of certain kinds of tiger moths, also enjoy these leaves, so don't automatically assume a larva on this plant is a monarch. Caterpillars of copper butterflies often favor dock, while certain swallowtails favor trees or vegetables.

Insects & Science