PestFacts WA

How to distinguish Fall armyworm caterpillars from other endemic caterpillars

With the recent detection of a fall armyworm (FAW) moth at Geraldton it is important that growers and consultants are able to distinguish fall armyworm caterpillars from other common caterpillars that may appear similar in appearance. For example, budworm caterpillars that are commonly found in the grainbelt can appear in variable colours, similar to the FAW caterpillar.

Distinguishing fall armyworm caterpillars from the usual armyworm caterpillars

Common armyworm caterpillars have three white stripes on their collar. The FAW differs from our endemic species of armyworm by having a spotted pattern of dots and a distinctive inverted white Y (see figure 1) which the common armyworm caterpillars do not have (Figure 2). FAW can also be found on pulse and canola crops which are not hosts for common and southern armyworm.

Figure 1: Defining characteristics of the fall armyworm caterpillar. Image courtesy of: DPIRD.

Figure 2: Characteristics of the common armyworm caterpillar. Image source: GRDC’s Insects of Southern Australian Broadacre Farming Systems Identification Manual and Education Resource 2nd Edition.

Distinguishing fall armyworm caterpillars from budworm caterpillars

FAW caterpillars can be confused with the native and lesser budworm caterpillars. FAW caterpillars, like budworm caterpillars, can appear in a range of colours. However, budworm caterpillars do not have a distinctive Y marking on the head area, as seen in Figure 3.

Figure 3: Characteristics of native budworm, corn earworm and lesser budworm caterpillars. Image source: GRDC’s Insects of Southern Australian Broadacre Farming Systems Identification Manual and Education Resource 2nd Edition.

What should you do if you suspect you have found FAW?

If you find a caterpillar that you suspect to be FAW please collect a sample. Place the caterpillar into boiling water for approximately 5 minutes as this denatures enzymic activity. Then place the caterpillar into 70% ethanol or methylated spirits and contact DPIRD entomologist Dusty Severtson on  +61 (0)427 196 656 to arrange for identification.

You can also take clear close-up photos of the caterpillar and plant damage and submit a report using the MyPestGuide Reporter app or contact DPIRD’s Pest and Disease Information Service (PaDIS) by email or phone +61 (0)8 9368 3080. Samples may then be requested as the only way to make a definitive identification for FAW is from examining a physical specimen. DPIRD entomologists cannot make a definitive identification from images.

For more information on FAW refer to DPIRD’s;

• Fall Armyworm in Western Australia page
• Fall armyworm larval identification guide fact sheet
• How to identify fall armyworm video
• 2020 PestFax Issue 10 Fall armyworm detected in the WA grainbelt article.

For more information contact Dustin Severtson, Research scientist, Northam on +61 (0)427 196 656. 

Article authors: Cindy Webster (DPIRD Narrogin), Svetlana Micic (DPIRD Albany) and Alan Lord (DPIRD South Perth).