On one of our butterfly trails in Camp Gee Dee we found a group of Dark blue tiger – Tirumala septentrionis and the Double branded crow – Euploea sylvester butterflies feeding on roots of plants . These butterflies belong to the danaid family also known as the milkweed family , thrive on the juices of poisonous plants .
They feed on the toxic alkaloids found in certain plants.This action is supposedly to extract the chemical pyrrolizidine alkaloids from these plants to aid in their defense mechanisms and also to produce pheromones. When a hungry bird pecks on them, it triggers a fearful physiological reaction in the predator’s body. This result in predators learning this memorable aspect at first hand. Predators soon associate the patterns and habits of such butterfly species with unpalatability to avoid hunting them in future. A great deal of sexual selection happens based on this. Females select the most distasteful males to ensure a safety of the progeny.
The potential predators remember that the Danaids are unpalatable and avoid them . An interesting study by Dr Tom Eisner and his colleagues at Cornell University, U.S.A., working with the tiger moth . He observed that tiger moths are rejected by certain orb weaving spiders, which cut them from their webs rather than eat them. The Cornell researchers have shown that the moths are unpalatable to spiders and to birds because of the pyrrolizidine alkaloids the caterpillars gather from their food plants. The spiders will eat moths from caterpillars reared on an alkaloid-free diet, but find even their palatable items, such as mealworms, unacceptable as food when alkaloids have been added. Amazing to know how the predators have adapted .
The click of the Danaid eggfly female has bee downloaded from Wikimedia Commons
Few Interesting links on how a Single Gene Controls Mimicry Across Different Species
A link on how one butterfly species can gain its protective color pattern genes ready-made from a different species by interbreeding with it — a much faster process than having to evolve one’s color patterns from scratch