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.
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.
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.
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).