Crawling, flying and slithering about the United States are thousands of insect species. Identifying these insects is complicated because most of them have a larval stage that looks completely different from how they will look as an adult. You can identify larvae through careful observation and a process of elimination. Cross-check observations against written descriptions and illustrations. Take photographs to avoid removing the larva from its environment or damaging it through handling. Find your first clue to identity in the larva's habitat. Find further clues in the size, shape, colour and eating habits.
Take a digital photograph of the larva if possible. Include a ruler next to the larva to record the size. If you have no ruler, place another recognisable object next to it to indicate the relative size. If you have no camera, record the size in your notebook.
Carefully scoop up the larva into the lidded container. Do not handle more than necessary. Provide some dirt and plant material from its habitat. Use a container of water from the habitat for aquatic larvae.
Note where you found the larva --- on water or land? If you found it on land, then you can exclude dragonflies, damselflies, mayflies and caddis flies. For non-aquatic larvae, list the type of habitat -- garden, field or forest; soil conditions and whether it was found alone, in a nest of similar larvae or associated with any adult insects.
Sketch the larva's shape. Many are distinctive. Note whether legs are present and if they are functioning legs -- as on a caterpillar --- or vestigial (partially formed).
Use the magnifying glass to study colour, markings and surface texture. Note whether it has a soft skin or a hard shell, lumps, spines, "horns" or hairs. Many beetle larvae and fly maggots are white or semi-transparent and are found underground. A grub with legs and markings will likely be a caterpillar. Record your findings. Make sketches if you have no camera. Return the larva to the place you found it.
Consult the insect book. Use the clues you have gathered to guide you to the right chapter. For example, if you have a large, white, curled-up grub with vestigial legs that was found underground, go to beetles. If you have an aquatic larvae with large jaws, go to the section on dragonflies.
Find an online identification source if you prefer. The University of Kentucky Entomology Department is spearheading provision of photographs of larval stages that are often omitted from insect identification tools.
Carefully compare the larvae (or your photograph and notes) to the illustrations and descriptions provided.
Find the best match using all the clues gathered from your close inspection. The published identification guides should give size and other data that will confirm or disprove your identification.
Do not always expect to identify the exact species. Insects are so varied and numerous that for more accurate identification you may need to consult a trained entomologist.