Bug of the Week: Seed Beetles

Ever wondered what makes holes in mesquite pods like these?


Here’s a hint:


See those tiny beige beetles feeding on the screwbean mesquite flowers?


Those are seed beetles. Other common names are pea or bean weevils, although they aren’t really weevils.

When I was in college we called them bruchids, because they belonged to the family Bruchidae. Now they have been moved to the leaf beetle family (Chrysomelidae) and are in the subfamily bruchinae. (Source: BugGuide)

The adult beetles lay their eggs in seeds, often of legumes like mesquite. The larvae are tiny grubs that feed inside the seeds. The larvae pupate, and when the time and conditions are right, the adult beetles chew out leaving a neat round exit hole.


Seed beetles are useful laboratory animals because they require little care.

For example, check out this animal behavior experiment on the movement of seed beetles that investigates whether seed beetles prefer to move horizontally or vertically.

Who knows where studying a tiny beetle can lead…


  1. Margarethe Brummermann

    Nice! Few people pay attention to Bruchids, sorry Bruchinae. I’ve collected and photographed about 12 spp so far in AZ. They are small but interesting. I just published a blog chapter about beetle larvae in AZ, but for practical reasons I had to stick to spp. that are not hidden inside seeds. Check it out!

  2. Roberta

    Very nice article on a subject that usually doesn’t get much attention. You have some awesome photographs.

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