Caterpillars and caterpillar-like larvae

 
  Hort Snacks - June 2013
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 Identifying Characteristics | Setae | Density of Hair | Body Features | Facial Features | Colours and Patterning | Other Features | Common Features of Various Caterpillar Families - Part 1 | Common Features - Part 2 | Common Features - Part 3 | Caterpillar-like Larvae

There are dozens of different insects that are found on and/or around horticultural crops which may or may not attack the crops. Some are aggressive and voracious and others just nibble at the fringes. Some are just present.

Caterpillars are the immature form of butterflies and moths, which fall in the order Lepidoptera. Caterpillars feed on all plant parts and grow rapidly through several stages until they enter a pupation stage.

Caterpillars have soft, segmented bodies, which are divided into 3 parts or segments. Each segment possesses a number of specific anatomical characteristics, which allows identification and differentiation. The 3 segments include:
1) Head – well-defined, toughened or sclerotized head capsule
2) Thorax – three segments bearing 1 pair of true legs per segment
3) Abdomen – ten abdominal segments with 3 to 5 pairs of fleshy/stubby prolegs (1 pair is typically on the last [anal] segment)



Caterpillars differ in a number of features or characteristics, giving them their variation in appearance. Some caterpillars are smooth and hairless, while others have differing lengths and densities of hair or spines. Colouration can also vary, as well as whether they have any striping, spotting or other distinctive features. If you get really up close and personal with a caterpillar, you can also tell the difference between species using more detailed or hard to see features, such as how the hooks on their anal proleg are arranged or what their face is shaped like.

Identifying Characteristics

Some of the identifying characteristics include:

Setae

Setae (sing = seta) – hair-like sensory projections from the skin of the caterpillar. Setae can range from long and flexible to short and stout or even inconspicuous. Some setae are on top of a projection of different shape or size. There are typically a minimum of 6 setae per side of each abdominal segment. The appearance and orientation of groups of setae (and number of setae per group) can be used for identification. Specific differences can be used to identify closely related species.

Differences in setae

Solitary
Solitary on projection
Projection with more than 1 seta
Disc-like area bearing parallel setae
Discs bearing divergent setae
Hair pencils – narrow cluster of long setae
Spinules – minute circular spines on surface of the caterpillar
Drawings by Robert Spencer

Density of Hair

No hair or inconspicuous
Dense hair
Sparse hair density
Tufts of hair
Drawings by Robert Spencer

Body Features

Prothoracic shield – a plate that may or may not be present on the top of the first thoracic segment; may be darkened

Spiracles – breathing holes on the side of the body, on all abdominal segments and the first thoracic segment. Appear as holes or dots along the sides of the caterpillar. Some species are quite distinctive (spiracles may be coloured, shaped a specific way or positioned uniquely).

Crochets – grasping hooks or hook-like structures on the ends of the prolegs. Length and arrangement of crochets can vary.

Complete circle
Semi-circle
Double rows
Single row
Drawings by Robert Spencer

Facial Features

Face grooves (technically referred to as adfrontal and epicranial suture) – can be used to differentiate certain types of caterpillars. The position or orientation of the frontal triangle is also used.

Front view of head
Drawing by Robert Spencer

Mandibles – jaws; Structure can vary somewhat, allowing differentiation between species.

Colours and Patterning

Body colour – can vary, including solid colours of different shades, such as black, brown, grey, blue, green, red, orange, yellow, white, etc.

Patterning – may be longitudinal or latitudinal (think racing stripe versus bumblebee), or may vary in shape or colour.

Solid colour
Camouflage
Spotted
Slashed
Banded
Striped
Drawings by Robert Spencer

Other Features

Other features – some species have dorsal horns, knobs, spikes, eyespots, etc.

Dorsal (back) horn or tail on segments
Knobs
Lashes
Head horns
Spines
Split tail
Example of a caterpillar with spines and a striped colouration
Example of a caterpillar with a tail (tuft) and various tufting and arrangement of setae
Drawings and Photos by Robert Spencer

Common Features of Various Caterpillar Families - Part 1

The following table outlines some of the common features of a number of families of caterpillars within the Order Lepidoptera, as well as the key characteristics of some species that are frequently or occasionally observed in this area. Please note: this is not a complete list of all pest species that occur in this area.

Family
Common Characteristics
Important Species - Common Names
Key Characteristics
Arctiidae
Very hairy appearance (long secondary setae); crochets on prolegs in single line
Saltmarsh caterpillar
Reddish brown, with yellow to brown bodies covered in short bristles and long whitish secondary setae; yellowish-brown head;
Woolly bear caterpillar
Body covered with dense tufts of stiff hair; reddish brown with black at both ends – other variations may have different coloured stripe.
Various Tussock moths
Dense clumps of “tussock” hairs on back (approximately 4 clumps); long setae; long pencils may be present
Yellow woolly bear caterpillar
(Photo by wikimedia.org)
Woolly bear caterpillar
(Photo by smithsonianscience.org)
Tussock moth caterpillar
(Photo by Robert Spencer)
Pieridae
Ringed body segments; many short secondary setae (velvety appearance); crochets in a single line parallel to midline
Imported cabbageworm
Light green larvae; narrow yellowish line on the back and a broken line on the sides; short white hairs gives a velvety appearance
Imported cabbageworm larva
(Photo by MAFRI)
Sphingidae
Large, fat, smooth, brightly coloured with inconspicuous setae; may have a distinct dorsal spine/horn on one abdominal segment; 4 ventral prolegs with crochets arranged in a single line; abdominal segments have wrinkles which give appearance of subsegments
Hawk moths, sphinx moths and hornworms
Medium to large and stout; 5 pairs of prolegs; lack hairs or tubercules; often have a dorsal horn; Some are green to brown, with “countershading” colouration; some are conspicuously coloured with spots on a dark background; diagonal slashes are common
Tomato hornworm
Large larvae; greenish to dark reddish brown; conspicuous v-shaped greenish-white marks on abdomen facing forward and slightly down; green anal horn; black spiracles within v-shaped mark (at point of mark).
Later stage tomato hornworm larva
(Photo by insects.about.com)
Sesiidae
Clearwing moths (wasp-like adults); larvae typically bore or burrow into host
Squash vine borer
Creamy white with brownish heads; prothoracic shield is yellowish; 4 pairs of less conspicuous prolegs with 2 rows of crochets;
Papilionidae
Larvae have a fleshy defensive organ (called an osmeterium) which is pushed out to emit an unpleasant odour;
Parsleyworm; Swallowtails
Large, smooth larvae; green to yellowish colour, with black lines and yellow or orange spots across segments; retractable “Y” or “V”-shaped defensive gland on the top of the 1st thoracic segment

Common Features - Part 2

Family
Common Characteristics
Important Species - Common Names
Key Characteristics
Gelechiidae
Small; light, inconspicuous primary setae; 4 ventral prolegs; variable crochets; many are internal-feeding insects
Potato tuberworm
Small, creamy-white to greenish or pinkish white larvae; very dark coloured head, prothoracic shield and true legs; crochets are in a complete circle;
Tomato pinworm
Small larvae; yellowish green to purple-black; purplish spots; head = dark with dark line on each side; yellowish prothoracic shield; crochets are in a semi-circle;
Peach twig borer
Reddish-brown with pale to white segments giving a ringed appearance; head and thorax dark brown to gray
Plutellidae
Diamondback moth
Small pale green to cream coloured larvae; conspicuous dark setae on all body segments; crochets are in a complete circle;
Diamondback moth larva
(Photo by Canola Council of Canada)
Noctuidae
Primary setae only; groupings of setae vary; crochets in single line
Cabbage looper
Move with a looping motion; pale green to blue-green; 3 pairs of wavy white stripes on top and sides of body;
Tomato fruitworm /
Corn earworm
Large larvae; vary from light green-yellow or pink to deep brown or almost black on the back; bottom side is usually light coloured; prominent dark tubercules (outgrowths); dark microspines on skin;
Cutworms
Pale to dirty brown; solid coloured or mottled; skin covered with microscopic bumps; differ from armyworms based on facial structure
Armyworms
Greenish-brown heads with lots of dark streaks and interlacing lines; backs are greenish-brown to black; paired dark markings; prolegs have dark diagonal band on outside
Cabbage Looper larvae
(Photo by U of Florida)
Red-backed cutworm larvae
(Photos by Robert Spencer)

Common Features - Part 3

Family
Common Characteristics
Important Species - Common Names
Key Characteristics
Pyralidae / Crambidae
Few or no secondary setae; groups of setae vary; 4 pairs of ventral prolegs; crochets in complete circle
Webworms
(garden webworm, beet webworm, etc.)
Greyish-green/yellow larvae; depending on species, may have either darker stripes down body or spots; beet webworms have two white or cream-colored stripes on either side of a black center line and two rows of paired circular marks down either side of the back
European Corn Borer
Dirty white larvae; backs are dark grey-brown to light brown; brown/black mottled head;
Tortricidae
Tortrix moths
Codling moth
Codling moth larvae are yellow with black heads
Ugly nest caterpillar
Yellowish-green bodies with small dark spots and dark heads, thoracic shields and anal shields
Large aspen tortrix
5 pairs of prolegs; yellowish or pale green bodies turning darker as they get larger and older; black heads, thoracic shields and anal patches; 2 rows of paired spots along the back of the body
Strawberry leaf roller
Slender, green or bronze to grayish brown larvae; brown-headed
Oblique-banded leafroller
Yellowish-green turning darker with age; black or brown head and thoracic shield
Lasiocampidae
Forest tent caterpillar
Black, hairy larvae; broad bluish lateral bands and narrow broken orange and brown lines on the body, with white/creamy-white keyhole-shaped marking on the back.
Geometridae
A.k.a. “inchworms”, “loopers”, “spanworms”; lack prolegs in centre of body, therefore move by clasping front legs and then lifting back end forward, clasping and repeating; often resemble twigs; seldom hairy
Fall cankerworm
Light green with white lines to brownish-green with dark band on back; 3 pairs of abdominal prolegs (1 rudimentary)
Spring cankerworm
3 pairs of prolegs; mottled yellow-green to blackish; may have yellow lateral stripes; pair of outgrowths end of the abdomen
Bruce spanworm
Stout bodied; 2 pairs of abdominal prolegs; colour ranges from light green to dark gray; 1 prominent and 2 less prominent yellowish stripes on each side of body or broad white stripes on side; dark brown to blackish heads

Caterpillar-like larvae

There are a number of species of insect that have larvae which resemble caterpillars (also known as eruciform larvae – caterpillar-like). Many of these are within the Order Hymenoptera, Suborder Symphyta (a.k.a. sawflies). There are a few characteristics that can be used to tell the difference between a true caterpillar (Lepidoptera) and a caterpillar-like larva. Why does it matter whether it is a caterpillar or a sawfly larva? This is because some pesticides are very specific to caterpillars (Lepidoptera) and will not work on sawfly larvae. For example, Bt (Bacillus thuringiensis) only works on caterpillars.

Lepidoptera – Butterflies, skippers and moths
Hymenoptera – Sawflies
Fake eye spots
Eye visible
Head end sometimes difficult to tell from tail end
Head obvious
3 pairs of jointed thoracic legs (true legs)
3 pairs of jointed thoracic legs (true legs)
5 or fewer pairs of prolegs (including anal proleg)
Enough pairs of prolegs to spell “SAWFLY” (6 or more pairs of prolegs
Anal claspers (anal proleg) always present
Anal claspers sometimes present
 
 
 
 
For more information about the content of this document, contact Robert Spencer.
This information published to the web on May 29, 2013.