Monarchs, Milkweed Bugs, Orange Assassin Bugs, and recently Margined Leatherwing Beetle are all insects I have observed on my inaturalist account within the same habitat. They all feature similar orange and black warning coloration. I have been wondering what causes this. I looked it up and mostly found posts explaining to gardeners what these bugs are. Does anyone know if this is directly caused by the milkweed in a similar way to how flamingos ingest shrimp causing their coloration? Or is this a convergent warning system to convey that they carry the same poison? I am very interested in the reason for this.
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I believe your latter guess is the correct one.
Beyond just convergence, it is a form of Müllerian mimicry where all the species share the same signaling of their toxic nature. Each bears a reduced burden of associative learning by predators, because predators don’t have to learn multiple warning systems through trial and error when they all share the same warning system.
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Thank you so much!
This will be one of the mysteries of nature. The answer to the question above I think is no. The insects mentioned evolve from preceding forms and the ancestors of these insects do not always subsist on milkweeds. There is a co-evolution factor. I’ve orange colour Assassin bug species over here found generally in parks. Milkweed species exist but not native to the region. Wild vines of the Apocynaceae family are present. Assassin bugs are predators of insects. These prey insects are not found on milkweeds. so the orange colour Assassin bugs are not associated with milkweeds over here. The Assassin bugs are classified in Heteroptera…/Reduviidae… The true bugs I casually call them stinkbugs, because they tend to produce an offensive odor if handled or just being around them. Insects can derive their defence system from the food they eat, as in the case of the butterflies. We know they take up pyrrolizidine alkaloids from flowers and plant sap. The other species of bugs like Dysdercus cingulatus have orange red and black colours too.These feeds on plants in the Malvaceae family many of which do not produce toxic compounds. Somewhere along the line of True bug evolution, a primitive species probably accquired the trait, the orange and black colour patterns, partly with inputs from the food they eat, the predators they encountered, and sometimes due to sexual selection, which is a part of natural selection.
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