Phytophagous insects in five orders, 50 families, 101 genera, and 114 species constitute the insect fauna ofMimosa pigraL., a weed introduced into northern Australia from tropical America. Most insect species attackingM. pigrain Australia were rarely or only occasionally encountered, are native or naturalized, polyphagous, and feed externally on the woody stems and mature foliage. Seventy-one species (62.3%) were known to breed on the plant, but only 13 (11.4%) were endophagous. No species were endophagous on flowers, fruit, seeds, or leaves. Thirty species (26.3%) are known pests of cultivated plants. Insects introduced into Australia for the biological control ofM. pigrawill find largely unexploited food sources, especially on new growth or inside the reproductive structures.