Which worms are which?

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
Figure 1: Black cutworm

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)

Common Armyworm
Figure 2: Armyworm (common or true)

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

Corn earworm (Helicoverpa zea)

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

Time of the year:

  • early June – mid-August
Western Bean Cutworm
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)
  • Western Bean Cutworm
    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)
Fall Armyworm
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:

  • Typically late August – September, but as early as July
Fall Armyworm
Figure 10: Fall Armyworm, highlighting square pattern of dots on last abdominal segment

Comparison of key features

Comparison of Key Features

More to come?

Which worms should I add to my cheat sheet? What tips do you have for ID? Let me know in the comment section.

Additional resources:

Photo: Heads of armyworm, fall armyworm, and corn earworm

Differentiating Black Cutworm, Fall Armyworm, and True Armyworm (www.aganytime.com)

Other Cutworms, Too Early for Black Cutworm (Purdue Pest & Crop)

Western Bean Cutworm and Its Look-Alikes (www.cornpest.ca) (pdf)

Whorl-feeding Worms in Late Corn (Purdue Pest & Crop) – This article has excellent photos comparing corn earworm and fall armyworm.

It’s All In The Ears Now (Field Crop News) – Several good photos, especially one comparing the heads of Corn Earworm and Western Bean Cutworm.

Western Bean Cutworm Management Strategy for Field Corn (OMAFRA)

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