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Quino Checkerspot Butterflies: Small, but Mighty

A century ago, millions of Quino checkerspot butterflies—their wings chequered with cheery red-orange, yellow, white and brown spots—swarmed the skies above Southern California in the United States. They thrived in the dry, scrubby landscape along the coast. Each about the size of a paper clip, the Quinos hatched in great numbers each spring.

Towards the end of the twentieth century, however, the development of farms and cities in the Los Angeles and San Diego areas in the state of California drastically reduced the butterfly’s habitat. By 1997, the Quino checkerspot population had declined to a tiny fraction of its historical numbers. That year, the United States designated the Quino checkerspot an endangered species.

The Quino’s situation continued to worsen. Many scientists believed it would soon be extinct. Wildfires burned much of its habitat, and temperatures were getting warmer and drier, making the environment more hostile to much of the flora in the area. These developments adversely affected the butterfly’s host plant, Plantago erecta, a small flowering plant commonly called the California plantain or dwarf plantain.

Scientists knew that Quino caterpillars relied on the dwarf plantain as a food source. Each spring, the adult female butterflies laid eggs on dwarf plantains. When the caterpillars hatched, they fed on the plantain leaves. However, in the hot, dry Southern California summer, the dwarf plantains wilted and died off. When this happened, the caterpillars responded by entering a state called diapause. They curled up into a ball and essentially stopped or slowed all bodily functions, just waiting for conditions to improve. Then, when normal winter rains came and the plantains bloomed again, the caterpillars revived and resumed eating. Once they’d grown large enough, the caterpillars entered the final stages of their life cycle, forming pupae and emerging as adult butterflies. This strategy worked well in most years, but as average temperatures rose and rainfall decreased, the plantains began dying earlier in the summer. The caterpillars weren’t getting sufficient food, and fewer developed into butterflies.

Biologists observed the situation with concern. Some recommended developing plans for ‘assisted colonisation’, or moving groups of the Quinos to new habitats where the plantains were healthier. But then the butterflies responded to the food shortage on their own. They set off for greener pastures.

Because the area where they lived was surrounded by developed cities and desert landscapes, the Quinos had limited options. They took off anyway, flying eastwards into the hills. They landed in mountainous open spaces east of the cities of Los Angeles and San Diego. They found no dwarf plantains there, but the Quinos adapted. The females began laying their eggs on the leaves of other plants, primarily the Collinsia concolor. These plants remained green longer into the summer months. When the caterpillars hatched, they successfully fed on the Collinsia leaves and enjoyed a longer feeding season. Quino checkerspots survived, and their numbers grew in their new home.

Scientists in the field were surprised when they began encountering numerous Quino checkerspots in the eastern hills. They were cheered to learn that these small insects had adapted to changing conditions. The Quinos demonstrated the resilience needed to survive by finding not only a new habitat, but a new food source, too.

Meanwhile, scientists at the San Diego Zoo had been raising Quino caterpillars in a laboratory as part of an effort to save the species from extinction. Working with the United States Fish and Wildlife Service, they released hundreds of caterpillars into protected areas around San Diego, hoping to rebuild the Quinos’ population in their historical range. Between the efforts of dedicated entomologists and the butterflies’ own actions, more of those colourfully chequered wings may soon be seen fluttering above the Southern California skies.