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Pest Control

Mexican Bean Beetle vs Ladybug: Count the Spots

Sixteen spots in three rows and a coppery body means bean beetle. Ladybirds are rounder, glossier, and are not the ones eating your leaves.

By Zakaria 2 min read Save to Pinterest — opens Pinterest in a new tab
Ladybug leaf
Photo: katerinavulcova, Pixabay Content License, via Pixabay
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Sixteen spots in three rows, coppery and matte means bean beetle. Seven glossy red spots means you are about to squash something useful.

Side by side

Adults
Mexican bean beetleLadybird
SpotsExactly 16, in rows of 8, 6, 27 or fewer, no fixed pattern
ColourCoppery orange-brown, matteRed or orange, glossy
Size6–7 mm5–8 mm
On whatBean leaves, feedingAnywhere there are aphids
DietLeavesAphids
Larvae — the easier call
Mexican bean beetleLadybird
ShapeOval, fatElongated, alligator-like
ColourBright yellowDark grey or blue-black with orange marks
TextureBranched black-tipped spinesSmooth with small bumps
WhereUndersides of bean leaves, in groupsHunting across foliage

If you only remember one thing

Spiny yellow larvae on a bean leaf is as close to definitive as garden identification gets. Ladybird larvae look like tiny alligators and are never bright yellow and spiny.

The damage pattern

Both adults and larvae feed on leaf undersides, scraping tissue from between the veins. The result is a lacy, skeletonised leaf with the vein network left intact — quite distinctive, and nothing a ladybird does.

Heavy populations defoliate plants and will move on to pods and stems. Several generations a season means damage accumulates through summer.

Organic control that works

  1. Handpick every few days — adults, spiny larvae, and the clustered yellow eggs on leaf undersides
  2. Row cover until flowering keeps them off young plants
  3. Clear crop debris at the end of the season — adults overwinter in it
  4. Rotate where beans are grown
  5. Pediobius foveolatus, a parasitic wasp, is used as a biological control where pressure is heavy

Handpicking sounds feeble and is genuinely effective at garden scale, because the eggs are laid in visible clusters of forty or so and removing one cluster removes forty beetles.

Other lookalikes in the same group

  • Squash beetle — closely related, larger spots, feeds on cucurbits
  • 28-spotted / hadda beetles (Epilachna spp.) — attack potatoes and aubergines in other regions

The pattern holds throughout: a ladybird-shaped beetle with many spots and a dull finish, sitting on damaged foliage, is worth identifying before you decide it is a friend.

Common questions

How do you tell a Mexican bean beetle from a ladybug?

Count the spots and look at the colour. Mexican bean beetles have exactly sixteen black spots arranged in three neat rows of eight, six and two across a coppery orange-brown back that is slightly duller and more matte than a ladybird's. Common ladybirds have seven spots or fewer in no particular arrangement and a glossier red shell. Behaviour settles it too: if the beetle is sitting on a bean leaf that is being skeletonised, it is almost certainly the pest, because ladybirds are there for aphids and do not eat leaves.

What are the yellow spiky larvae on my bean plants?

Mexican bean beetle larvae. They are bright yellow, oval, and covered in branched black-tipped spines, and they feed on the undersides of bean leaves in groups, which is where most of the damage comes from. Ladybird larvae look entirely different — elongated, dark grey or blue-black with orange markings, and alligator-shaped rather than spiny and round. Finding spiny yellow larvae on beans is as close to a definitive identification as you get.

What damage does a Mexican bean beetle do?

Both adults and larvae feed on the undersides of leaves, scraping away the tissue between the veins and leaving a lacy skeletonised appearance that is quite distinctive. Heavy infestations can defoliate plants, and the beetles will also feed on pods and stems when leaf material runs out. Yields drop sharply on badly affected plants, and the damage accumulates because there can be several generations in a season.

How do you control Mexican bean beetles organically?

Handpicking is genuinely effective in a garden. Check leaf undersides every few days and remove adults, the yellow spiny larvae, and the clusters of yellow eggs, which are laid on the underside in groups of forty or so. Row cover until flowering excludes them from young plants, clearing crop debris at the end of the season removes overwintering adults, and rotating where beans are grown helps. Where populations are heavy, the parasitic wasp Pediobius foveolatus is used as a biological control.

Are there other ladybird lookalikes that eat plants?

Yes, and they belong to the same subfamily. The squash beetle is closely related and looks similar with larger spots, and feeds on cucurbits. Worldwide there are other leaf-eating Epilachna species, often called 28-spotted or hadda beetles, which attack potatoes, aubergines and related crops. The general rule holds: a ladybird-shaped beetle sitting on damaged foliage with many spots and a duller finish is worth identifying before you assume it is a friend.

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