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 (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

Corn earworm (Helicoverpa zea)

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

Time of the year:

• early June – mid-August

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)

• 

  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 (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

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)