ENTFACT-017

RECOGNIZING INSECT LARVAL TYPES

By Lee Townsend, Extension Entomologist

Insects develop from egg to This key is like a path with a series of forks along the
adult in a process called way. A choice is made at each fork that will send you
metamorphosis which may toward an answer. The end point will be a drawing of
be generally classified as one of the common larval types that should resemble
either gradual or complete. your specimen.
Gradual metamorphosis has
three stages – egg, nymph, Start- The first decision along the identification path
and adult. Nymphs generally look much like their adult is whether or not the larva has segmented thoracic
stage except for being smaller and lacking wings, if the legs. If it does, you stay on the first page of the key.
species has winged adults. Common examples include If it does not, then go to the second page.
stink bugs, grasshoppers, and cockroaches.
Larvae with segmented thoracic legs and fleshy
About 75% of all insect prolegs
species go through the four Look at the abdomen for relatively distinct pairs of
stages of complete fleshy legs. Caterpillars (Order Lepidoptera) are
metamorphosis - egg, larva, immature stages of butterflies and moths; they have 5
pupa, and adult. The larva or fewer pairs (Box 1). These plant feeders have
is a specialized feeding chewing mouthparts. Often, caterpillars have “hairs”,
stage that looks very spines, or distinct coloring. Those with 4 or fewer
different from the adult. pairs of these legs are called “loopers” or
Fortunately, there are just a “inchworms” because of the distinctive way that they
few basic larval types and they are relatively easy to crawl.
recognize. Often, insect identification must be based on
the larval stage because no adults are present. Being Larvae with pairs of fleshy legs on all abdominal
able to recognize larval types can tell you a lot about segments (Box 2) are called sawflies (Order
the insect, For example, is it a plant feeder, predator, or Hymenoptera). They often occur in groups on
a scavenger? Are any management or control practices deciduous trees or evergreens.
necessary? This publication is designed to help you to
follow a series of choices in a process to recognize the Larvae with segmented thoracic legs but no fleshy
basic type of the insect that you have. prolegs
Larval types with segmented thoracic legs but no
Basic terms: fleshy abdominal legs are shown in Boxes 3 and 4.
Head – usually a dark, often hard capsule at front of These types are found in many species of beetles
body. It may be partly covered by the thorax. In (Coleoptera) and some lacewings (Neuroptera) The
some larvae, a hard or distinct head may be absent decision at this point is more subjective. Larvae with
or completely hidden. relatively long thoracic legs and a relatively
Thorax – three segments immediately behind the streamlined, often pointed bodies are shown in Box 3.
head. A pair of segmented legs usually is attached These predators are active crawlers that hunt prey.
to each. These segments may be fused together Usually, they have a relatively flat heads and
rather than being separate and distinct. prominent forward-pointing jaws. Examples are a)
Abdomen - eight to 10 body segments immediately lacewing, b) lady beetle, and c) ground beetle.
following the thorax.
Segmented thoracic legs – three pairs of segmented or Larvae in Box 4 have shorter, thicker thoracic legs, a
jointed legs that are found on the body segments more box-shaped head, and wider abdomen. They
immediately behind the head. can crawl but tend to be slow and deliberate. Soft,
Fleshy legs- usually short, often paired, unsegmented white bodied forms, like the white grub and
extensions from the underside of the abdomen that rootworm, live in protected places while leaf feeders
are used for movement. and scavengers tend to have harder, more protected
bodies. White grubs (a) often occur in soil, decaying
organic matter, rotting logs, etc. Wireworms (b) have hidden within the thorax. These dingy gray larvae
hard, cylindrical, bodies. Many species live in soil live in decaying organic matter.
feeding on seeds or roots or in decaying wood. 12 – Rat-tailed maggots have long distinct tails that
Rootworm larvae (c) live in the soil and feed on plant are extensible breathing tubes which allow them to
roots. Leaf beetle larvae (d), like that of the Colorado live in very stagnant water.
potato beetle, resemble caterpillars without fleshy
abdominal legs. They feed exposed on foliage. Hairy 13 – Flatheaded wood borers have a distinct wide
carpet beetle larva (e) are scavengers that feed on area behind their heads and a long white, soft body.
plant and animal products. They may be found in The dark head is withdrawn into the thorax but part
stored products or natural fibers, such as cotton or of it usually is visible. These borers live in tree limbs,
wool. branches, and stems.

Larvae with no segmented thoracic legs (Page 2) 14 – Roundheaded wood borers are similar to
These are highly specialized larvae; most live in flatheaded borers but do not have the wide area
water, soil, wood, or in decaying organic matter. behind the head.
Some species have distinct, usually dark heads while
others do not. 15 – Fly maggots have no head and a cream to white
body that is distinctly tapered at head and blunt at the
Legless larvae with distinct heads rear. Many flies have this larval type including blow
Most of these larvae are beetles or flies (Diptera). flies, house flies, and fruit flies.
Each of the pictures represents a larval type.
16 – Aphid predator maggots are headless, they tend
5 – Weevil grubs can be found in plants, plant tips, to have green tinged bodies and are found wandering
seeds, nuts, or with plant roots in the soil. The on leaf surfaces where they feed on aphids. They are
underside usually is flat while the upper side is good crawlers and resemble small caterpillars but
rounded, giving them a humpbacked appearance. lack a distinct head and legs of any sort.

6- Midge larvae occur in water or moist organic There are thousands of variations of these basic forms
litter. There is a single fleshy leg at the front and back but it is usually possible recognize its basic features and
of the body. They are the immature stages of varies to place the specimen in one of the main groups. Help
species of gnats. with larval identification is available thru your local
Cooperative Extension office.
7- Mosquito larvae (wiggler) are very distinctive.
The thorax is wider than the abdomen and many Life cycle drawings are from:
species have a distinct air tube at the end of the http://everest.ento.vt.edu/~idlab/vegpests/vegi/stinkb
abdomen. These larvae live in still water. ug.green.jpeg
http://www.entomology.umn.edu/cues/4015/morpology
8 – Drain fly larva have narrow, strap-like plates /complete.jpg
across the upper surface. They live in standing,
stagnant water, and especially seldom used drains.

9 – Fungus gnat larvae resemble midge larvae but do

not have fleshy legs. They live in moist, decaying
organic matter, especially accumulations of fallen
leaves or dead grass.

10 – Soldier fly larva has a flat, gray, palm-shaped

body with a distinct tapered head the protrudes from
the front. They are common in compost piles and
decaying organic matter.

Head mostly hidden or no distinct head

These larvae either do not have distinct visible heads
or the head is withdrawn almost completely into the
thorax. They are fly larvae that with one exception
live in wet or moist areas.

11 – Crane fly larvae often have fleshy lobes at end

of their abdomens. The distinct head is completely