Which worms are which?

Dennis Van Dyk

10 years ago

I’m just terrible at recognizing people that I don’t know very well — coming up with their name or even where I know them from (as I think many in the vegetable industry have noticed). So embarrassing — I’m definitely in the wrong line of work. And then I also have to try to be able to identify all kinds of crop pests, too, although that’s usually not as hard for me. But I do find it challenging to remember which worm is which sometimes, so here’s a cheat sheet I use. Maybe it will help you, too. They are listed in approximate order of appearance.

Black cutworm (Agrotis ipsilon)

Distinguishing features:

Colour ranges from gray to almost black
Indistinct narrow stripe along the centre of the back
Granular skin texture (see closeup in Purdue Pest & Crop article)
Dark-coloured head
Four pairs of abdominal prolegs, plus one pair at back end

Time of the year:

early May – mid-June

Armyworm, common or true (Mythimna unipuncta)

Distinguishing features:

White-bordered stripes running along the body
Dark, diagonal bands at the top of each abdominal proleg (four pairs); plus one pair of prolegs on back end
Yellow-brown head with a network of fine, dark lines

Time of the year:

late May – early July

Figure 3: Armyworm (common or true), highlighting bands on prolegs

Corn earworm (Helicoverpa zea)

Figure 4: Corn Earworm, highlighting light coloured, freckled head

Distinguishing features:

Alternating dark and light stripes along back
Stripe down each side of the body
Range in colour from pink to green to olive-brown to brown
Light-coloured, often orange-freckled head — see a photo gallery of corn earworm, with photos showing the range of variation of the head at OSU Vegnet
Four pairs of abdominal prolegs, plus one pair at back end
Small bumps with spiny hairs

Figure 5: Corn Earworm, highlighting small bumps with spiny hairs

Time of the year:

early June – mid-August

Figure 6: Western Bean Cutworm, highlighting rectangles behind head

Western bean cutworm (Striacosta albicosta)

Distinguishing features:

In tiny first and second instar larvae, spots with short hairs and dark-coloured head
Early instars move like inchworms
Four pairs of abdominal prolegs, plus one pair at back end
Large gap between true legs and prolegs (see photo comparisons on this www.cornpest.ca pdf)
In older larvae, absence of stripes, spots, or hairs and a pair of dark rectangles just behind the head (see photos on Purdue website)
Figure 7: Western Bean Cutworm

Older larvae are tan to pink in colour

Time of the year:

July-August

Variegated cutworm (Peridroma saucia)

Distinguishing features:

A line of yellowish dots along the back
Smooth skin
Mottled gray to brown colour, usually with some orange stripes; pale underside
Net-like pattern on head
Four pairs of abdominal prolegs, plus one pair at back end
Curls into a C-shape when disturbed

Time of the year:

July – August (small overwintering population may be present in May-June)

Figure 8a: Variegated cutworm

Figure 8b: Variegated cutworm

Figure 9: Fall Armyworm, highlighting Y pattern on head

Fall armyworm (Spodoptera frugiperda)

Distinguishing features:

White, inverted “Y” on the front of the head
Faint net-like pattern on head
Green to tan to almost black
Set of pale stripes along back; darker stripes along each side
Elevated spots with spiny hairs; four spots on last abdominal segment form a square
Four pairs of abdominal prolegs, plus one pair at back end; no black bands on prolegs
See a fall armyworm photo gallery at OSU Vegnet

Time of the year: