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Pest of the Month - Mimosa Webworm

Mimosa Webworm, Nebraska Extension Acreage Insights September 2017.
Mimosa Webworm

Mimosa webworms are web building caterpillars that infest mimosas (plants, not the drinks) and honeylocust trees. The caterpillars web foliage together to create a silken home from where they can skeletonize leaves. As they feed, patches of the tree’s leaves will brown taking on a “scorched” appearance.

Pest description

As adults, mimosa webworms are dull colored moths. They have a half inch wingspan and are grey in color with small black dots on their wings. Their eggs are small, oval, and white but will turn rose-colored as they near hatching. The caterpillars are about an inch long when mature. In terms of color they are gray to dark brown with five white stripes and a brown head. If disturbed they will drop down from trees on a silken line.

Life history

Adults emerge in late May or early June to begin mating and laying eggs. These first eggs and caterpillars will fully mature into moths by the end of July or beginning of August. These early summer moths that emerge will mate and begin a second generation of caterpillars that feed until September. Once the second generation finishes feeding, they will leave the tree and construct a pupae on nearby buildings or trees in order to overwinter. These cocoons will produce moths the next spring to begin the cycle anew.

Integrated pest management tactics

The mimosa webworm prefers thorn-less varieties of honeylocust. Avoiding cultivars like “Sunburst” will help to prevent dealing with the webworm in the future. Preferable cultivars would be “Shademaster” or “Imperial”. Owners who are proactive can scout their trees and use a pole pruner to remove visible nests in June or July. There are insecticidal options as well including; bifenthrin, carbaryl, chlorantraniliprole, cyfluthrin, and malathion amongst others. Organic control options include spinosad and Bt products applied in June to control caterpillars while they are small. Thorough coverage will be needed no matter what is applied and an arborist may be needed in some cases. Spray for first generation larvae in June and second generation larvae in August.

Image of Jonathan Larson
Jonathan Larson
Extension Educator - Entomology

Jonathan Larson is the Nebraska Extension entomologist for Douglas and Sarpy counties. His main focus is lawn and landscape pests but he also helps with bed bugs, roaches, and any other home invader that has six or more legs. Jonathan has his Bachelor of Science in Entomology from Purdue University, and his Ph.D. in Entomology from the University of Kentucky.

Contact Jonathan at:
Douglas/Sarpy County Extension
8015 W Center Rd.
Omaha, NE 68124-3175
(402) 444-7804