Large Milkweed Bugs

Alert reader and careful insect observer Patrick O'Malley sent the picture below showing a particularly large cluster of large milkweed bugs (Oncopeltus fasciatus).  In my experience, large milkweed bugs have become much more abundant in the past few years than they were previously.  I don't know why that is.  Maybe gardeners are paying more attention to milkweed plants now that they are searching for monarch caterpillars.  Or maybe this previously southern and eastern species is surviving better in Iowa because of warmer winters.

Whatever the reason, finding milkweed bugs on milkweed seed pods in the last half of summer is not cause for alarm.  The orange and black milkweed bugs feed on sap from the seed pods without disturbing monarch butterfly caterpillars and other insects that may be on other parts of the plant.  

Milkweed bugs are harmless unless you are saving seeds to propagate in your butterfly garden; the milkweed bugs may further reduce already-low germination rates.

Random thought: milkweed bugs are brightly colored as a warning to would-be predators (warning coloration).  Milkweed bugs accumulate toxins from the milkweed plant which might harm a predator that tries to eat more than two.  Predators learn to avoid distasteful prey, and the bright colors reinforce the memory.  "Don't eat another one!"

cluster of large milkweed bugs on milkweed leaves and pods


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