A lady beetle that has turned vegetarian. The adults are coppery orange with 16 black spots and look like large ladybugs; the larvae are bright yellow and covered in branched spines. Both chew the underside of bean leaves, leaving the upper skin as a lacy, see-through window that dries and falls out. Snap and lima beans are the favourites. Row covers, early trap plantings and pulling infested plants do most of the work in a garden, and the parasitoid wasp Pediobius foveolatus can be bought and released each summer.
Larva and adult Epilachna varivestis on a snap bean leaf. Photo: pending.
Adults are oval and dome-shaped like any lady beetle, about 6–7 mm (1/4 in) long in Florida's Featured Creatures; Maryland Extension gives 1/3 in. They start out straw-yellow, then darken with age to coppery orange-brown, with eight black spots on each wing cover — 16 in all, in three rows. The Maryland extension describes the rows as 6, 6 and 4 across the back. Adults are slow, drop to lower leaves or the ground when disturbed, and ooze drops of an offensive yellow fluid from their leg joints.
Telling it from a ladybug: the eating is the giveaway — this beetle is on the bean leaves, not on aphid colonies, and the leaves are lacy where it sits. The larvae settle it. Predatory lady beetle larvae are alligator-shaped, black and spiny with bright spots; Mexican bean beetle larvae are oval, yellow and covered in large forked spines. The only other plant-eating lady beetle most gardeners meet is the squash beetle, which feeds on squash, pumpkin and cantaloupe and has fewer spots — seven, in Kentucky Extension's description.
Adults and larvae feed on the underside of the leaf between the veins and leave the upper skin intact. That skin dies and turns papery, so the leaf looks like lace, and the dead patches later fall out. The larvae do more damage than the adults. Heavy infestations can strip plants completely, and in bad years beetles also eat flowers and small pods. Bean plants tolerate some leaf loss, but the sources differ on how much: Maryland Extension says up to 20% before yield falls, while UMass Extension says feeding damage over 10–20% can cause yield loss.
Adults spend the winter in leaf litter, hedgerows and woodland edges, and fly to beans as the weather warms — seeking out snap and lima beans from mid-May in Florida's Featured Creatures account, and usually moving into fields in June in Massachusetts. After a week or two of feeding, each female lays 500–600 eggs in clusters under the leaves. Larvae feed for two to five weeks, then fasten themselves under a leaf to pupate. Numbers usually grow with each generation, and UMass Extension notes they may not reach damaging levels until August. There are one to three generations a year, and generally two in the mid-Atlantic.
Snap and lima beans are the preferred hosts, and wax beans are especially favoured. Florida's Featured Creatures notes that lima beans are less preferred than snap beans. Cowpea, black-eyed pea, soybean and mung bean are poorer hosts but are still damaged when they grow near snap or lima beans. The beetle has also been recorded on alfalfa and clover.
We found no published home-garden number. Maryland Extension says beans tolerate up to 20% leaf loss before yield drops; UMass Extension says damage over 10–20% can cause yield loss. The commercial threshold UMass Extension suggests is more than 20% defoliation before bloom, or 10% during pod formation, when plants are most sensitive. If you plan to release Pediobius, do not wait for a threshold: release when the first eggs hatch.
From early summer, turn bean leaves over and look for the yellow egg clusters, the bright yellow larvae and the lacy windows they make. Adults and larvae are easy to spot. If you plan to release Pediobius, the date the first eggs hatch is the date that matters.
The parasitoid wasp Pediobius foveolatus is the biological control that UMass and Maryland Extension recommend buying and releasing. It lays its eggs inside the beetle larvae, which die and turn into brown mummies. It comes from India and fails to overwinter in the US, so it must be released every year. Florida's Featured Creatures notes that early, widespread annual releases can suppress the beetle on soybean. The New Jersey Department of Agriculture's beneficial insect lab rears and sells it, supplies it to New Jersey bean farms and community gardens, and credits the lab with more than 100,000 acres of soybean protected from the beetle. UMass Extension reports a good track record in the mid-Atlantic and among New England growers who have tried it. Florida's Featured Creatures counts at least 17 predators of the eggs, larvae and pupae, and it shows the spined soldier bug eating a larva.
In a garden, keeping beetles off the plants and destroying infested plants does more than spraying. Maryland Extension's advice is built around row covers and trap plantings.
Rating: the effect on this pest's natural enemies if a spray hits them or they feed on treated plants. REI is the re-entry interval on farm and greenhouse labels; home labels usually give none, so follow the label.
Sanchez-Arroyo, Mexican bean beetle, UF/IFAS Featured Creatures EENY-15 (1997, rev. 2015)
University of Maryland Extension, Mexican Bean Beetle – Vegetables (2023)
UMass Extension Vegetable Program, Mexican Bean Beetle (Hazzard, Brown & Cavanagh, 2013)
University of Kentucky ENTFACT-702, Ladybugs
NJ Dept. of Agriculture, Phillip Alampi Lab: Mexican Bean Beetle Outreach Project (2026)
UC IPM Pest Management Guidelines: Cucurbits — Squash Bug; Asparagus — Asparagus Beetles (REIs)
UC IPM, Bee Precaution Pesticide Ratings (pyrethrins, carbaryl)
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
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