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How to identify it
- Adults are rounded, very convex, ladybug-shaped beetles with 16 black spots, eight on each wing cover in three rows across the body. Length is about 6 to 8.5 mm by Cornell's measure, 1/4 to 1/3 inch by Clemson's, and about 5/16 inch (8 mm) by Purdue's.[1][3][5]
- Newly emerged adults are yellow; older and overwintering adults are coppery brown.[1][6]
- Larvae are bright yellow, oval and soft-bodied, with six rows of branched spines tipped in black. Grown larvae reach about 8 mm, or 1/3 inch.[1][3][5]
- Eggs are yellow, about 1.2 mm long, and laid standing on end in clusters on the underside of leaves.[1][6][2]
- Pupae are yellowish orange and fastened to leaves, stems or pods by the larva's old spiny skin.[1][5]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Lady beetles (beneficial) | Lady beetles look very much like it and are close relatives, but they eat aphids and other insects, while the Mexican bean beetle eats bean foliage.[2][1] |
| Squash beetle | The other lady beetle that feeds on vegetable crops. It goes after squash-family plants; Clemson's example was a spiny larva under a cucumber leaf.[4] |
Where it lives
Native to Mexico, it was found only in the western United States until it was introduced into Alabama in 1920; by 1938 nearly every state east of the Mississippi had populations. Purdue notes it is frequently found in parts of the Midwest, including southern Indiana.[1][5]
Biology and life cycle
Adults spend the winter in ground cover in sheltered places such as hedgerows and woods next to fields, and in the Northeast move into bean plantings in June. Purdue adds that they also overwinter in soybean crop debris.[1][2][5]
Some adults leave their overwintering sites when the earliest beans come up, while others wait nearly two months. Females feed for a week or two before laying eggs.[3]
Eggs hatch in 5 to 14 days depending on temperature. Larvae feed for about 2 to 5 weeks, pupate on the plant, and adults emerge about 10 days later.[1][3]
Egg to adult averages 33 days in Cornell's figures, about a month in Clemson's, and 30 to 40 days in summer but closer to 60 when it is cool in UMass's.[1][3][2]
Cool, moist weather favors heavier infestations, while hot weather suppresses the beetle; numbers usually grow with each generation, so later plantings and late summer see the most damage.[1][2]
When disturbed, adults 'reflex bleed', releasing blood that carries a defensive alkaloid shown to deter spiders and ants. Newly emerged adults build up the compound within days; eggs and larvae lack it.[7]
Damage and signs
- Larvae and adults feed on the underside of leaves between the veins. The leaf tissue dies in a lace-like pattern, and patchy yellow and brown areas can show on the upper surface.[1][2][6]
- Larvae usually do more damage than adults. On soybean the leftover veins often fall out in wind or rain, leaving large ragged holes.[5]
- Snap and lima beans are favored hosts; dry beans and soybeans are also attacked, and when numbers are high the beetles feed on stems and pods too.[2][1][3]
- Heavy infestations can cut yields by 20% to 50%. UMass notes that feeding damage over 10 to 20% can cause yield loss, and plants are most sensitive while pods are filling.[1][2]
- The beetle also spreads several soybean viruses, including bean pod mottle virus, and in choice tests it was more attracted to virus-infected soybeans than to healthy ones.[8]
Health risk
It is a plant pest. The sources describe damage to bean foliage, stems and pods, and none describes it biting people.[1][2][3]
Control
Prevention
Plant very early or in late summer to miss the peak of damage, which comes in July and August. An early-planted trap crop can draw overwintered adults so that control can be focused there.[1][3]
Reflective metallic or white plastic mulch reduces beetle numbers and feeding compared with black plastic or bare ground. Clemson lists the snap bean varieties 'Wade' and 'Black Valentine' as resistant or tolerant.[2][1][3]
Keep them out
Cover bean rows with row cover to keep beetles out until harvest, or for as long as practical.[2]
Sanitation
Destroy crop residue promptly after harvest, by working it into the soil, composting it, or mowing, disking or flaming on a farm, to cut the number of beetles that overwinter.[2][3]
Traps and physical control
On a small scale, check leaf undersides for yellow egg clusters, larvae and adults and remove them by hand, since most of the population is on the foliage.[1][3]
Biological control
Pediobius foveolatus, a tiny (1 to 3 mm) non-stinging parasitic wasp, lays its eggs in bean beetle larvae; about 25 wasps emerge from each parasitized larva. It is sold for release, works best released when the first eggs hatch, and must be released every year because it does not survive the winter. UMass suggests at least 10 to 15 parasitized larvae ('mummies') for a home garden.[2][1]
Pesticides
UMass suggests treating only above about 20% defoliation before bloom or 10% during pod formation, with good coverage of lower leaf surfaces, and keeping sprays away from Pediobius releases. Follow the label of any product used.[2][1]
In Virginia snap beans, neonicotinoid-treated seed controlled the beetle only when beetles arrived within 2 to 3 weeks after planting; otherwise it gave little benefit.[9]
Where sources disagree
Generations per year: NC State says one on soybean in North Carolina; Cornell says two in the Northeast and Purdue two overlapping generations in the Midwest; UMass says two or three; Clemson says usually three in South Carolina, sometimes a partial fourth.[6][1][5][2][3]
Egg cluster size: Cornell and UMass give 40 to 50 eggs, Clemson 20 to 50.[1][2][3]
Adult size: Cornell gives 6 to 8.5 mm, Clemson 1/4 to 1/3 inch and Purdue about 5/16 inch (8 mm).[1][3][5]
Common questions
- Is this a good ladybug or a bad one?
- If it's copper-colored with 16 black spots and you find it on beans with lacy leaves, it's likely the Mexican bean beetle, a close relative of lady beetles that eats bean leaves rather than other insects.[2][1]
- What are the fuzzy yellow bugs under my bean leaves?
- Probably Mexican bean beetle larvae. They are bright yellow with rows of black-tipped spines, and they feed on the leaf undersides alongside the adults.[1][3][5]
- Why are my bean leaves turning lacy?
- Mexican bean beetles feed on the underside of leaves between the veins, and the remaining leaf tissue dies in a lace-like pattern.[1][2][3]
Sources
- Cornell University, New York State Integrated Pest Management, “Mexican Bean Beetle, Epilachna varivestis (Vegetable IPM Fact Sheet, December 2025).” cals.cornell.edu/integrated-pest-management/outreach-education/fact-sheets/mexican-bean-beetle-epilachna-varivestis-vegetable-ipm-fact-sheet (accessed 2026-11-11)
- UMass Amherst Center for Agriculture, Food, and the Environment, “Mexican Bean Beetle (vegetable fact sheet).” www.umass.edu/agriculture-food-environment/vegetable/fact-sheets/mexican-bean-beetle (accessed 2026-11-11)
- Clemson Cooperative Extension Home & Garden Information Center, “Bean & Southern Pea Insect Pests (HGIC 2203).” hgic.clemson.edu/factsheet/bean-southern-pea-insect-pests/ (accessed 2026-11-11)
- Clemson Cooperative Extension Home & Garden Information Center, “What Is It? Wednesday: Squash Beetles (Ballew 2023).” hgic.clemson.edu/what-is-it-wednesday-squash-beetles/ (accessed 2026-11-11)
- Purdue University Department of Entomology, Field Crops IPM, “Mexican Bean Beetles (Soybean).” ag.purdue.edu/department/entm/extension/field-crops-ipm/soybean/mexican-bean-beetles.html (accessed 2026-11-11)
- NC State Extension, “Mexican Bean Beetle in Soybean (Soybean Insect Factsheets).” content.ces.ncsu.edu/mexican-bean-beetle-in-soybean (accessed 2026-11-11)
- Experientia, via PubMed, “Defensive alkaloid in blood of Mexican bean beetle (Eisner et al. 1986).” pubmed.ncbi.nlm.nih.gov/3753941/ (accessed 2026-11-11)
- Genome Biology and Evolution, via PubMed, “A sweet story: Bean pod mottle virus transmission dynamics by Mexican bean beetles (Smith et al. 2017).” pubmed.ncbi.nlm.nih.gov/28204501/ (accessed 2026-11-11)
- Environmental Entomology, via PubMed, “Effects of thiamethoxam-treated seed on Mexican bean beetle, nontarget arthropods, and crop performance in southwestern Virginia snap beans (Nottingham et al. 2017).” pubmed.ncbi.nlm.nih.gov/29069307/ (accessed 2026-11-11)
- iNaturalist, “Epilachna varivestis taxon page (order and family).” www.inaturalist.org/taxa/219319 (accessed 2026-11-11)