ENTFACT-017: Identify types of insect larvae |Download PDF
by Lee Townsend, extension entomologist
College of Agriculture at the University of Kentucky
Insects develop from egg to adult in a process called metamorphosis, which can generally be classified as gradual or complete. The gradual metamorphosis consists of three stages - egg, nymph and adult. Nymphs generally look very similar to the adult stage, except they are smaller and wingless if the species has winged adults. Common examples include bed bugs, grasshoppers, and cockroaches.
About 75% of all insect species go through the four stages of complete metamorphosis - egg, larva, pupa and adult. The larva is a specialized feeding stage very different from the adult. Fortunately, there are only a few basic larvae types and they are relatively easy to spot. Often insect identification must be based on the larval stage due to the absence of adults. Being able to recognize the types of larvae can tell you a lot about the insect. For example, is it a herbivore, predator, or scavenger? Are management or control practices required? This post aims to help you make a number of decisions to identify the basic type of insects you have.
Insect metamorphosis: Gradual (left) and complete (right)
basic terms:
- Kopf- usually a dark capsule, often hard on the front of the body. It may be partially covered by the rib cage. In some larvae, a hard or prominent head may be absent or entirely hidden.
- Breast– three segments immediately behind the head. Each usually has a pair of segmented legs attached. These segments can be merged instead of being separate and distinct.
- Abdomen- eight to ten body segments immediately after the thorax.
- segmented sternums- three pairs of segmented segments or
jointed legs that meet at the body segments immediately behind the head. - meaty legs- usually short, often paired, unsegmented processes of the lower abdomen, which are used for movement.
this keyit is like a path with a series of forks along the way. At each fork, a choice is made that leads to an answer. The last item will be a drawing of one of the most common species of larvae, which your specimen should resemble.
Begin- The first decision on the way to identification is whether or not the larva has segmented sternums. If so, stay in the first section of the key. If not, go to the second page.
SECTION 1: Larvae with segmented sternums and fleshy forelimbs
Look at the belly to see relatively different pairs of meaty legs. Caterpillars (order Lepidoptera) are immature stages of butterflies and moths; they have 5 pairs or fewer (Box 1). These herbivores have chewing mouthparts. Caterpillars often have "hair", spines, or a distinctive coloration. Those with 4 or fewer pairs of these legs are called "loopers" or "inchworms" because of their characteristic way of crawling.
Larvae with fleshy pairs of legs on all abdominal segments (Box 2) are called sawflies (order Hymenoptera). They are usually found in clusters on deciduous or evergreen trees.
Larvae with segmented sternums but no fleshy forelimbs
Larval types with segmented sternums but no fleshy ventral legs are shown in boxes 3 and 4. These types are found in many beetle species (Coleoptera) and some lacewings (Neuroptera). The decision at this point is rather subjective. Larvae with relatively long sternums and relatively streamlined, often pointed bodies are shown in Box 3. These predators are active crawlers that hunt their prey. Typically, they have relatively flat heads and prominent, forward-facing jaws. Examples are a) lacewings, b) ladybugs and c) ground beetles.
Larvae in Box 4 have shorter, thicker sternums, a more boxy head, and a broader abdomen. They can crawl but tend to be slow and deliberate. Soft, white-bodied forms like the white larva and caterpillar live in sheltered locations, while leafeaters and scavengers tend to have harder, more sheltered bodies. White grubs (a) are often found in soil, rotting organic matter, rotting logs, etc. Wireworms (b) have hard, cylindrical bodies. Many species live in the soil, feeding on seeds or roots or decaying wood. The caterpillar larvae (c) live in the soil and feed on plant roots. Like the Colorado potato beetle, leaf beetle larvae (d) resemble caterpillars without fleshy ventral legs. They feed exposed in the foliage. The larvae of the hairy carpet beetle (e) are scavengers that feed on plant and animal products. They can be found in stored products or in natural fibers such as cotton or wool.
Types of Insect Larvae Image Key: Section 1 (Click on the image to enlarge)
SECTION 2: Larvae without segmented sternums
These are highly specialized larvae; Most live in water, soil, wood, or decaying organic matter. Some species have prominent, usually dark, heads, while others do not.
Legless larvae with distinct heads
Most of these larvae are beetles or flies (Diptera). Each of the images represents a larval type.
5 - Weevil larvae can be found on plants, plant tops, seeds, nuts or with plant roots in the soil. The underside is usually flat while the top is rounded, giving them a humped appearance.
6- Mosquito larvae are found in water or moist organic bedding. There is a single fleshy leg at the front and back of the body. They are the immature stages of several mosquito species.
7- Mosquito larvae (wigglers) are very different. The thorax is wider than the abdomen and many species have a distinct trachea at the end of the abdomen. These larvae live in still water.
8 – Drain fly larvae have narrow, strap-like plates on top. They live standing
standing water and particularly infrequently used drains.
9 - Fungus gnat larvae are similar to sand gnat larvae but lack fleshy legs. They live in damp and decaying environments.
organic matter, especially accumulations of leaves or dead grass.
10 – The soldier fly larva has a flattened, gray, palm-shaped body with a prominent conical head from which it protrudes.
forward. They are common in compost heaps and decaying organic matter.
Head mostly hidden or no distinct head
These larvae either have no clearly visible head or the head is almost completely retracted onto the thorax. These are fly larvae that, with one exception, live in wet or damp rooms.
11 - Crane fly larvae usually have fleshy lobes at the end of the abdomen. The prominent head is completely hidden in the thorax. These filthy gray larvae live in decaying organic matter.
12 – Rattail larvae have long, prominent tails that are extendable breathing tubes that allow them to live in very stagnant water.
13 – Flat-headed borers have a distinct wide area behind their head and a long, smooth white body. The dark head is retracted into the thorax, but part of it is usually visible. These borers thrive on twigs, twigs and logs.
14 - Round head drills are similar to flat head drills but lack the broad area behind the head.
15 – Fly larvae are headless and have a cream to white body, tapering sharply at the head and blunt at the back. Many flies have these types of larvae, including blowflies, house flies, and fruit flies.
16 - Predatory larvae of aphids are headless, tend to have green colored bodies and migrate to leaf surfaces where they feed on aphids. They are good trackers and resemble small caterpillars but lack any distinctive head and legs.
Types of Insect Larvae Image Key: Section 2 (Click on the image to enlarge)
There are thousands of variations on these basic forms, but it is usually possible to identify their basic features and place the specimen in one of the main groups. Contact your local Cooperative Extension office for help identifying the larvae.
The life cycle drawings are from:
Virginia Tech - Department of Entomology
University of New Mexico - Entomology
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Images: University of Kentucky Entomology unless otherwise noted