Description

Micromus posticus, the golden-brown lacewing, is a species of brown lacewing belonging to the family Hemerobiidae in the order Neuroptera. Adults are physically larger than other species within the family, measuring between 7.0 mm and 9.5 mm in length. Adults possess two pairs of large, hairy, membranous wings, many-segmented beaded antennae and large golden eyes. Brown lacewings are frequently confused with green lacewings, which are members of the family Chrysopidae and are not always green. However, they can be distinguished by the presence of forked coastal cross veins of the wings, a characteristic unique to members of Hemerobiidae.

Larvae are elongate and tapered towards the rear end. Dorsal coloration is generally cream, gray, or white, with prominent sickle-shaped mandibles that curve inward. Eggs measure less than 1 mm in diameter. They are initially cream-colored, but turn dark pinkish brown shortly before larvae hatch.

At least eight similar species occur in the U.S. and at least 100 are described worldwide. Species identification requires detailed study of adult anatomy, especially wing veins and male genitalia. Online distribution records of the genus may not be accurate unless verified by specialists of Neuroptera.

Life Cycle

Micromus posticus is the most commonly encountered species within the genus in the U.S. and is common in Louisiana. Its distribution extends across North America from Massachusetts to Minnesota, south to Mexico, and extending as far north as Manitoba. The species occurs in a wide variety of habitats, including mixed forests, citrus groves, pecan orchards, vineyards, and fields of alfalfa, cotton and potatoes. Golden-brown lacewings undergo four distinct life stages: egg, larva, pupa, and adult. Larvae typically hatch three to four days after eggs are laid. Newly hatched larvae feed primarily on small aphids, drink from water droplets, or, in the absence of other food sources, may engage in cannibalism, consuming other larvae and eggs. Larvae progress through three growth stages (instars) that are distinguishable by increasing head capsule size. The first instar lasts one to five days, the second instar lasts one to two days, and the third instar, which is notably more active, lasts one to four days. Following the third instar, larvae form a loosely spun, two-layered cocoon within bracts or leaf folds, where they undergo pupation for two to five days before emerging as adults. Females lay eggs for approximately seven weeks, depositing around 1,000 eggs on fibrous substrates such as cotton fibers or spider mite webbing. Peak development occurs during the summer, with adults becoming common by early fall. Adult lifespan ranges from nine to 12 weeks, with males typically living longer than females.

Ecological Significance

Golden-brown lacewings are predatory in both larval and adult stages and feed predominantly on aphids. Aphid prey species include Aphis gossypii (cotton aphid), Myzus persicae (green peach aphid), Toxoptera citricida (black citrus aphid), Brevicoryne brassicae (cabbage aphid) and Monelliopsis pecanis (yellow pecan aphid). They may also feed on other insects, such as eggs of Pieris rapae (imported cabbage worm). Aphids are small insects that feed on plants by sucking sap out, causing extensive damage to crops if infestations are heavy. They also vector many plant diseases. Larvae of Micromus posticus have been documented consuming approximately 40 aphids each. Given the aphid feeding nature of the species, it is regarded as a valuable biological control agent. In fact, a closely related species, Micromus tasmaniae, has been successfully mass-reared for biological control purposes in Australia. However, using species for biological control in areas where they are non-native is ecologically risky. In some instances, Micromus posticus larvae have been observed preying on other beneficial species, including ladybug eggs and even consuming eggs of their own species. Additionally, adult golden-brown lacewings have been observed biting holes in the mummies of parasitized aphids to feed on the tiny wasps within, which are also valuable biocontrol agents. Predators such as golden-brown lacewings along with many other natural enemies of aphids are valuable natural control agents in agricultural systems. Unfortunately, they are highly susceptible to pesticides sprayed for aphid control. Expert scouting for both pests and natural enemies is required for science-based decisions in pest management that maximize conservation of natural enemies whenever possible.

References

Klimaszewski, J., and K.M. Kevan. 1988. The brown lacewing flies of Canada and Alaska (Neuroptera: Hemerobiidae) Part III. The genus Micromus Rambur. Giornale italiano di Entomologia 4: 31-76.

Miller, G.L., and R.D. Cave. 1987. Bionomics of Micromus posticus (Walker) (Neuroptera: Hemerobiidae) with descriptions of the immature stages. Proceedings of the Entomological Society of Washington 89: 776–789 (accessed 24 March 2025).

New, T.R. 2002. Prospects for extending the use of Australian lacewings in biological control. Acta Zoologica Academiae Scientiarum Hungaricae, 48(Supplement 2): 209–216 (accessed 24 March 2025).

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