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How to identify it
- All five species are small flea beetles, 3 to 4 mm long, that walk or jump on their enlarged hind legs when disturbed even though they can fly. Their root-feeding larvae do the same damage, so identification depends on the adults.[1]
- Brown-legged flea beetle (A. lacertosa) adults are shiny black and about 3 mm with largely reddish-brown legs, sometimes with dark patches on top of the hind thighs. The black flea beetle (A. czwalinai) is the other black species and has solid black hind thighs. The black species emerge earlier in spring than the brown ones.[1]
- Black dot flea beetle (A. nigriscutis) adults are just over 3 mm, orangish brown, and usually carry a black dot on the back near the front edge of the wing covers. The other brown species, A. cyparissiae and the more orange A. flava, look much like it, and color differences among the brown species are often unreliable.[1]
- Larvae are slender, whitish grubs with a brown head, 1 to 6 mm long, found only by digging and cutting open spurge roots. Adults are easiest to spot around spurge shoot tips through the summer.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Glyptina flea beetles | Twelve native brownish flea beetles, some of which turn up in leafy spurge stands east of the Rockies. They are only 1 to 2 mm long, against 3 to 4 mm for Aphthona.[1] |
Where it lives
All are European. The black dot flea beetle was first released on leafy spurge in Canada in 1983 and moved to the United States from 1989; the brown-legged flea beetle was released in several states from 1993, often in mixed-species lots. Both are now widespread and abundant on leafy spurge across the United States. In Minnesota, almost every county takes part in leafy spurge biocontrol and the brown-legged flea beetle is the species that has proven particularly effective.[1][2]
Biology and life cycle
Each species has one generation a year. Larvae overwinter in the roots and resume feeding on young roots in early spring as the spurge starts to grow, then pupate in the soil.[1]
Adults are active from early to late summer, feeding on spurge leaves and flowers as the plants bolt, bloom and set seed. Females lay many eggs in the soil through the growing season, and the hatching larvae burrow into the roots, feeding on root hairs and young roots through three larval stages.[1]
The species sort themselves by site. The brown-legged flea beetle does best in moderately dense spurge on loamy soils and tolerates both dry and wet ground in the United States, but not very sandy or clay soils. The black dot flea beetle prefers sparse spurge on dry sites with sandier soil, succeeds in open, warm, very dry places with light soils, and is scarce or absent on moist, sheltered, heavy ground.[1]
Black dot flea beetle populations can be held back by a bacterium that skews the sex ratio toward females.[1]
Damage and signs
- Larval feeding on root hairs and young roots cripples root function and stunts the stems, and at some sites opens the roots to soil pathogens; adult feeding on leaves and flowers cuts the sugar the plant can store in its roots. It is the larval root feeding that damages or kills the plant.[1][2]
- Together the brown-legged and black dot flea beetles are significantly reducing leafy spurge density at the local level in most regions of the United States, though they fail at some sites. In Minnesota control is successful at many sites statewide and takes 3 to 10 years depending on the size of the patch, the density of spurge and the weather, with small controlled areas usually appearing first.[1][2]
- In an Idaho trial along streams where herbicides are restricted, releasing 50 beetles per flowering stem in two consecutive years cut spurge biomass and crown and stem density by 60 to 80 percent at all three sites, while 10 per stem gave inconclusive results.[3]
- Nontarget feeding is minor: no effects are reported for the brown-legged flea beetle, and spillover feeding by black dot adults on the native Euphorbia robusta in Wyoming had no effect on that plant's populations and faded as leafy spurge declined.[1]
Health risk
These are plant-feeding flea beetles and weed biological control agents; none of these sources describes any risk to people.[1][2][3]
Control
Prevention
Match the beetle to the site: brown-legged flea beetles for moderately dense spurge on loam, black dot flea beetles for sparse spurge on dry, sandy ground. Heavy, moist, sheltered sites suit neither well.[1]
Biological control
The flea beetles are the control. Minnesota's Department of Agriculture and DNR run a statewide leafy spurge program in which beetles are collected from established sites and released at new ones; expect control to take 3 to 10 years.[2]
Where an established population can be collected in large numbers, heavy releases of about 50 beetles per flowering stem in two successive years have suppressed small, isolated spurge patches along streams where herbicides cannot be used.[3]
Common questions
- How do I tell the leafy spurge flea beetles apart?
- Start with color. Black bodies mean A. lacertosa (reddish-brown legs) or A. czwalinai (solid black hind thighs). Brown bodies mean A. nigriscutis (usually a black dot on the back), A. cyparissiae or the more orange A. flava, but the brown species are hard to separate by color alone.[1]
- The adults are everywhere but the spurge is still there. Are they working?
- Adults on the shoot tips are a sign the larvae are in the roots, which is where the damage happens and where it cannot be seen without digging. Control typically takes 3 to 10 years, and small cleared patches appear before the whole stand goes.[1][2]
- Will these flea beetles attack my garden plants?
- They are specialists on leafy and cypress spurge. No nontarget effects are reported for the brown-legged flea beetle, and the only spillover recorded for the black dot flea beetle was light adult feeding on a native spurge in Wyoming with no effect on its populations.[1]
Sources
- North American Invasive Species Management Association (PDF hosted on Bugwood), “Milan (Bureau of Land Management), West (USDA ARS), Bourchier (Agriculture and Agri-Food Canada) and Randall (USDA Forest Service). Spurge Biocontrol Agents: History and Ecology in North America. In: Winston, ed., Biological Control of Weeds in North America, NAISMA-BCW-2024-40-SPURGES-A (2024).” bugwoodcloud.org/resource/files/29180.pdf (accessed 2026-11-10)
- Minnesota Department of Agriculture and Minnesota Department of Natural Resources, “Biological Control of Invasive Plants in Minnesota (Chandler, Skinner and Van Riper).” files.dnr.state.mn.us/natural_resources/invasives/biocontrolofplants.pdf (accessed 2026-11-10)
- Journal of Economic Entomology (Entomological Society of America), “Progar (USDA Forest Service), Markin, Milan, Barbouletos and Rinella. Inundative release of Aphthona spp. flea beetles (Coleoptera: Chrysomelidae) as a biological 'herbicide' on leafy spurge in riparian areas. Journal of Economic Entomology 103: 242-248 (2010), doi:10.1603/ec09294.” doi.org/10.1603/ec09294 (accessed 2026-11-10)
- iNaturalist, “Aphthona lacertosa taxon page (order and family).” www.inaturalist.org/taxa/455493 (accessed 2026-11-10)