African armyworm

Spodoptera exempta (Walker, 1856) · formerly or also: Laphygma exempta

viwavijeshi (vya Afrika) · Swahili, East Africa
chenille légionnaire africaine · French, Central and West Africa
black armyworm / nutgrass armyworm · English, Southern Africa and Australia

The African armyworm is a moth whose caterpillars appear suddenly in huge numbers after the first rains, especially following a drought, and 'march' across pastures and cereal fields, stripping them to the ground. Outbreaks can cover thousands of square kilometres. Because moths migrate on storm winds from one outbreak area to the next, national and regional forecasting services track them with trap networks and warn farmers.

African armyworm caterpillar on a grass leaf. Photo: ChriKo, CC BY-SA 4.0, via Wikimedia Commons.

Type: Insect · Insect (moth); outbreaks of caterpillars
Classification: Animalia › Insecta › Lepidoptera › Noctuidae
Main crops: Maize, Sorghum, Millet, Rice, Wheat, Pasture and rangeland
Found in: East Africa, Southern Africa, West and Central Africa, Arabia, Asia and Oceania
Chemical groups: IRAC 3A, IRAC 15, IRAC 31 (mode-of-action groups, not products)
Last reviewed: 2026-10-20

African armyworm scientific name, order and family

The scientific name of African armyworm is Spodoptera exempta (Walker, 1856), in the order Lepidoptera, family Noctuidae.

Older or alternative scientific names: Laphygma exempta.

Where it occurs

Sub-Saharan Africa, especially East and southern Africa, and the Arabian Peninsula; also present in parts of South and Southeast Asia, Australia and Pacific islands, where outbreaks are less frequent.

Region	Status
East Africa	Native; frequent, large outbreaks
Southern Africa	Native; regular outbreaks
West and Central Africa, Arabia	Present; occasional outbreaks
Asia and Oceania	Present; sporadic outbreaks

Symptoms and identification of African armyworm

Armyworm caterpillars crossing bare ground during an outbreak. Photo: ChriKo, CC BY-SA 4.0, via Wikimedia Commons.

The organism

Caterpillars change colour with crowding: at low density (solitary phase) they are green to brown and inconspicuous; in outbreaks (gregarious phase) they are velvety black on the back with thin pale lines along the sides and a pale or green underside, up to about 3 cm long. They lack the inverted Y and four-spot square of the fall armyworm. Moths are dark grey-brown with a wingspan of about 3 cm.

Signs in the crop, stage by stage

Crop stage	What you see
Seedling cereals and pasture	Sudden appearance of masses of black caterpillars that eat leaves down to the stems, often starting in pastures and grassy field edges.
Vegetative cereals	Large areas of crop eaten bare; caterpillars move in bands to neighbouring fields; leaves skeletonised by young larvae.
After an outbreak	Bare fields with frass; larvae disappear into the soil to pupate within two to three weeks.

Life cycle of African armyworm

Life cycle of African armyworm — diagram drawn by Laisha from the stages below. Durations depend on temperature.

Moths lay egg batches on grass leaves, often after migrating on winds associated with storm fronts. Larvae feed for two to three weeks and pupate in the soil. Each outbreak generation can produce moths that start a new outbreak downwind, so outbreaks move across a region during the rainy season.

Stage	Duration	Notes
Egg batch	About 2-5 days	Up to several hundred eggs per batch, covered with scales.
Larva (6 instars)	About 14-22 days	Black and gregarious at high density.
Pupa in soil	About 7-12 days	A few centimetres deep.
Adult moth	About 1-2 weeks	Strong migrant on wind.

Temperature

Development is fastest in warm conditions (about 25-30 °C); outbreaks are linked more to rainfall patterns than to temperature.

Generations

Several generations during the rainy season; outbreaks shift geographically from generation to generation.

Conditions that favour it

The first heavy rains after a dry period, when fresh grass growth and moth concentration by storm winds coincide; extensive grasslands near crops.

Economic threshold level (ETL)

There is no field-level numeric threshold in general use: outbreaks are sudden and devastating, so action is triggered by outbreak reports and forecasts from national armyworm services and by finding larvae in or next to fields.

Thresholds are local. They depend on crop price, control cost, variety and natural-enemy activity, so use the figure your local extension service publishes where one exists.

Damage and yield loss from African armyworm

Outbreaks can destroy cereal seedlings and pasture over large areas, forcing replanting and causing feed shortages for livestock; losses in affected fields can be total.

Monitoring

National and regional services run pheromone and light trap networks and issue outbreak forecasts based on moth catches and rainfall.
Check pastures and field edges after the first rains for young larvae, and report outbreaks to extension services.

How to control African armyworm (integrated management)

Control works best as a sequence: prevent, monitor, then act only when a threshold or a risk forecast says so, using the least disruptive option that works.

Cultural control

Act on forecasts: inspect crops daily when outbreaks are reported nearby and replant quickly if seedlings are lost.
Keep field margins of grass short where practical, and avoid leaving pasture adjacent to young cereals unmonitored.

Mechanical and physical control

Ditches dug in front of advancing larvae can trap them in small areas.

Biological control

Spodoptera exempta nucleopolyhedrovirus causes natural collapses of outbreaks and has been tested as a sprayed biopesticide with good results in East Africa; parasitoids, birds and predators also kill many larvae.

Host resistance

No resistant cereal or pasture varieties are available.

Chemical control of African armyworm — by mode-of-action group only

Laisha names chemical options only by their resistance-committee mode-of-action group (IRAC for insects, mites and nematodes, FRAC for fungi, oomycetes and bacteria, HRAC for weeds), never by active ingredient or product. What is registered differs by country and changes over time; the label and your local plant-protection authority decide what may be used, on which crop, at what rate and with what pre-harvest interval.

Insecticides are used during outbreaks, often through government campaigns, targeting young larvae. What is registered differs by country and changes over time; follow the label and your local plant-protection authority.

Scheme	Group	Mode of action	Notes
IRAC	3A	Sodium channel modulators (pyrethroids)	Fast-acting outbreak control.
IRAC	15	Inhibitors of chitin biosynthesis, CHS1 (benzoylureas)	Selective; young larvae.
IRAC	31	Baculoviruses	Nucleopolyhedrovirus where registered.

Resistance management

Resistance has not been a major issue because outbreaks are sporadic; rotate groups in repeated campaigns and use biological options where possible.

Look-alikes and how to tell them apart

Fall armyworm — Feeds in the maize whorl rather than marching in bands; inverted Y on the head and four dark spots in a square near the tail.
Cutworms — Grey-brown larvae that cut seedlings at soil level at night and hide in soil by day.
Desert locust hopper bands — Marching grasshopper nymphs with legs for jumping, not caterpillars.

Host range

Grasses and cereals: pasture and rangeland grasses, maize, sorghum, millets, rice, wheat, barley, teff and sugarcane seedlings; sedges such as nutgrass. Broadleaf crops are rarely attacked.

What is still uncertain

Forecast accuracy depends on trap networks and rainfall data that are incomplete in many areas.
The relative importance of outbreaks outside Africa is poorly documented.

Grow guides for its host crops

How to grow the crop well is the first line of defence. Laisha's free grow guides cover each crop from sowing to harvest:

How to grow Maize How to grow Sorghum How to grow Millet How to grow Rice How to grow Wheat

Not sure this is what you are seeing?Ask Laisha: describe the symptoms or send a photo, and get a reasoned first read with what to check next — for your crop, your stage and your region.Ask Laisha

Sources

Spodoptera exempta (black armyworm) datasheet — CABI Compendium. https://doi.org/10.1079/cabicompendium.29809
Spodoptera exempta (LAPHEX) — EPPO Global Database. https://gd.eppo.int/taxon/LAPHEX
Forecasting the severity of seasonal outbreaks of African armyworm — Bulletin of Entomological Research (Cambridge). https://doi.org/10.1017/S0007485300052366
Evaluation of Spodoptera exempta nucleopolyhedrovirus for the field control of African armyworm — Crop Protection (Elsevier). https://doi.org/10.1016/j.cropro.2007.04.005

Written by Laisha from the sources above, in its own words. This page is general reference, not a prescription: confirm identification locally and follow the label and your plant-protection authority.