Monarch butterflies are world-famous for their stunning annual migration. Because different milkweed species grow in various environments, monarchs can be found in a wide range of habitats, such as prairies, wetlands, pastures, parks, and gardens. For all monarchs, milkweed is an essential feature of their habitat. The North American population can be separated into two groups: eastern monarchs that overwinter in central Mexico, and western monarchs that overwinter primarily in central California. Monarchs are native to North and South America, but have spread to other regions including Europe and the South Pacific. While not typically fatal to monarchs, OE negatively impacts their survival, size, and life span, adding to the already monumental threats that monarchs face. OE infections occur when monarch larvae consume parasite spores that have fallen from an infected adult to milkweed leaves it is most often transmitted from adults to their offspring. A protozoan parasite called Ophryocystis elektroscirrha (OE) is the most-studied monarch parasite. While not all parasites kill their host, they almost always negatively affect them. Parasites are smaller organisms that live and multiply inside the host, snatching nutrients and resources away. Fly and wasp parasitoids often lay their eggs on monarch larvae, sometimes resulting in the monarch’s death. Parasitoids are specialized insects that lay eggs inside other insects and develop by feeding in or on their host. Though tiny, parasites and parasitoids also pose a threat to monarch survival. Their two main avian predators, black-backed orioles and grosbeaks, seem to be immune to monarch toxins and consume the insects in large numbers however, this may be due to the decay of monarch toxins during their migration and overwintering. Adult monarchs must be wary of birds, one of the most common natural causes of monarch mortality in their overwintering locations. As larvae, other invertebrates, including ants and wasps, will attack. Despite this defense, monarchs are still vulnerable to predation in all stages of life. As caterpillars and adults, monarchs have striking colors that warn other animals of their toxicity, resulting from their milkweed diet as larvae. Sadly, the future of these glorious creatures is in doubt-and the western monarch population is in an especially precarious state. They range from Mexico northward to Canada in two populations: one on the eastern side of the Rocky Mountains and a significantly smaller group on the western side. With their incredible migrations of up to 3,000 miles and annual overwintering aggregations in the trees of Central Mexico and California, monarch butterflies are celebrities among insects and true butterfly royalty. Monarch butterflies Danaus plexippus are perhaps one of the most recognizable butterfly species in North America, known for their bold black-and-orange markings and milkweed-fueled metamorphosis from egg to adult.
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