The seven-spotted ladybug sports a bright red with black dots to signal that it is toxic and unpleasant to the taste: it is aposematism, a warning coloring which dissuades predators from biting it before they even taste it.
The mechanism: reflex and bitter bleeding
When it feels threatened, the ladybug practices "reflex bleeding": it releases by the joints of its legs droplets of yellowish hemolymph, loaded with alkaloids such as coccinelline. This liquid is bitter and toxic to many birds and small mammals, which spit out the insect and learn to avoid its livery. Red and black, very contrasting colors visible even from a distance, serve precisely to memorize this unpleasant experience: a predator that has tasted it once will then avoid any similar silhouette.
This system only works if the signal is reliable: a ladybug that deceives about its toxicity would quickly lose its effectiveness. This is why the coloring is stable and recognizable within the same species, contrary to popular belief.
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Seven points, one species, not one age
Contrary to widespread belief, the number of points on the elytra does not indicate the age of the insect: it is genetically fixed and characteristic of the species. Coccinella septempunctata always bears seven, whatever its age; other species of ladybugs display two, fourteen, or even none, with different patterns. The color may fade slightly just after metamorphosis then settles permanently within a few hours.
Beyond its chemical defense, this ladybug provides a valuable agricultural service: larvae and adults are formidable predators of aphids, a single one being able to consume several dozen per day, which makes it a natural auxiliary appreciated for limiting the use of insecticides on crops.
