Description of mimosa webworms
The mimosa webworm (Homadaula anisocentra) is an occasional pest of honeylocust trees in Iowa. Caterpillars feed on the foliage and tie the leaflets together in tightly compressed, protective webs. Affected foliage gradually turns brown. There are two generations of caterpillars per year. Extensive damage is most obvious following the second generation in August.
Life cycle of mimosa webworms
Mimosa webworm moths emerge in early June and lay their eggs on the leaves of the honeylocust trees. The first generation caterpillars are usually present from mid-June to early July. Moths emerge again in mid- to late July and lay eggs for a second generation of caterpillars that feed from early to late August. Caterpillars grow to almost 1 inch in length. They are grayish-brown to light orange and have five light-colored stripes running the length of the body. Caterpillars often drop from infested trees on thin strands of silk.
Damage caused by mimosa webworms
The occurrence of mimosa webworm and the amount of damage vary greatly from tree to tree and from year to year. The Sunburst variety of the thornless honey locust is most susceptible to webworm attack. Extensive damage has not been common during the past decade but scattered, isolated reports of noticeable damage have been reported. Damage from the mimosa webworm is seldom serious to otherwise healthy, well-established trees. The webs and browned foliage are unsightly and caterpillar silk hanging from the trees may be annoying. The damage is more aesthetic than serious.
Management of mimosa webworms
Chemical control for mimosa webworm is rarely warranted. A treatment after foliage has turned brown is ineffective and a waste of time. Such late treatments do more harm than good by destroying the natural enemies of the pest rather than the pest itself. Sprays must be applied at the start of the caterpillar period and before webbing is apparent to be effective (mid-June and again in early August).
Do you live in Iowa and have an insect you would like identified?
The Iowa State University Plant & Insect Diagnostic Clinic will identify your insect, provide information on what it eats, life cycle, and if it is a pest the best ways to manage them. Please see our website for current forms, fees, and instructions on preserving and mailing insects.
Contact information for each states diagnostic laboratory for U.S. residents. If you live outside of Iowa please do not submit a sample without contacting the Plant & Insect Diagnostic Clinic.