…Could be the name of a Halloween party cover band, don’t you think? But in fact, these are the common names for Pyraloidea adults and larvae, respectively. Pyraloidea is the third largest superfamily of the Lepidoptera, and is comprised of two families – Pyralidae and Crambidae. Together, there are about 16K species worldwide.
Within the group, there is incredible diversity of feeding habits. Larvae feed on corn, rice, and other grains and grasses, ferns, fruit and vegetable crops, potted tree seedlings, and even excretions of sloths and bats. Some species have larvae that are fully aquatic – very rare indeed for a baby moth or butterfly! Common names “CRANBERRY GIRDLER” and “GRASS-VENEER MOTH” also reflect feeding behavior.
Adults are called ‘snout-moths’ because of the long, upturned labial palps on the mouth region of the head (FIGs. 1 and 2).
Adult snout moths are slender and hold their wings folded over their back when at rest. Wing patterns vary by species. These moths fly low and usually in a zig-zag pattern; this habit can be useful when scouting.
Larvae are slender, white to cream-colored caterpillars with tan heads. They have 3 thoracic (true) prolegs and 5 abdominal prolegs and can therefore be confused for cutworms (earning them a spot on my blog here!). Figure 3 shows identifying characters of webworms. The comparative ID guide for cutworms can be viewed here.
Larvae vary in color from black to green to tan depending on food source, species, and age. Raised, sclerotized areas of the integument look like brown ‘spots’ along the body. The spots become more prominent with age but be careful: cranberry girdler’s spots are the same color as the integument and therefore not obvious. Mature larvae range from 5/8 to 3/4 inch long.
DAMAGE & MONITORING
Cranberry girdler is more difficult to detect and control than other, related sod webworms because it typically feeds at or below the thatch layer. This species is sometimes called ‘subterranean webworm’. Digging and sifting through soil is one way to detect the presence of larval webworms, but if an infestation is suspected, the most effective way to confirm it is to pour 2 gallons of a soap solution over an area of about 1 square yard. This irritates the larvae and causes them them to come to the surface. 5 webworms per square yard is considered to be an action threshold in most grasses.
Sod webworm seems to thrive in drought conditions, so regular watering can help reduce the risk. Various products are registered, consult the PNW Insect Management Handbook for suggestions. Mid-summer is the best time to apply treatments, because larvae overwinter deep in the soil column and therefore are harder to reach in fall and spring.