Butterflies rest on flowers at the Butterfly Pavilion of the Natural History Museum of Los Angeles County in Los Angeles, the United States, May 27, 2019. The butterfly exhibition at the Natural History Museum of Los Angeles County showcases hundreds of butterflies and the plants that surround them. (Xinhua/Li Ying)

A visitor takes photos of a butterfly at the Butterfly Pavilion of the Natural History Museum of Los Angeles County in Los Angeles, the United States, May 27, 2019. The butterfly exhibition at the Natural History Museum of Los Angeles County showcases hundreds of butterflies and the plants that surround them. (Xinhua/Li Ying)

Butterflies rest on leaves at the Butterfly Pavilion of the Natural History Museum of Los Angeles County in Los Angeles, the United States, May 27, 2019. The butterfly exhibition at the Natural History Museum of Los Angeles County showcases hundreds of butterflies and the plants that surround them. (Xinhua/Li Ying)

A butterfly rests on a photographer at the Butterfly Pavilion of the Natural History Museum of Los Angeles County in Los Angeles, the United States, May 27, 2019. The butterfly exhibition at the Natural History Museum of Los Angeles County showcases hundreds of butterflies and the plants that surround them. (Xinhua/Li Ying)

A butterfly is seen among flowers at the Butterfly Pavilion of the Natural History Museum of Los Angeles County in Los Angeles, the United States, May 27, 2019. The butterfly exhibition at the Natural History Museum of Los Angeles County showcases hundreds of butterflies and the plants that surround them. (Xinhua/Li Ying)

A butterfly rests on leaves at the Butterfly Pavilion of the Natural History Museum of Los Angeles County in Los Angeles, the United States, May 27, 2019. The butterfly exhibition at the Natural History Museum of Los Angeles County showcases hundreds of butterflies and the plants that surround them. (Xinhua/Li Ying)

A butterfly is seen on leaves at the Butterfly Pavilion of the Natural History Museum of Los Angeles County in Los Angeles, the United States, May 27, 2019. The butterfly exhibition at the Natural History Museum of Los Angeles County showcases hundreds of butterflies and the plants that surround them. (Xinhua/Li Ying)

A butterfly rests on flowers at the Butterfly Pavilion of the Natural History Museum of Los Angeles County in Los Angeles, the United States, May 27, 2019. The butterfly exhibition at the Natural History Museum of Los Angeles County showcases hundreds of butterflies and the plants that surround them. (Xinhua/Li Ying)

Butterflies rest on leaves at the Butterfly Pavilion of the Natural History Museum of Los Angeles County in Los Angeles, the United States, May 27, 2019. The butterfly exhibition at the Natural History Museum of Los Angeles County showcases hundreds of butterflies and the plants that surround them. (Xinhua/Li Ying)

A butterfly is seen on leaves at the Butterfly Pavilion of the Natural History Museum of Los Angeles County in Los Angeles, the United States, May 27, 2019. The butterfly exhibition at the Natural History Museum of Los Angeles County showcases hundreds of butterflies and the plants that surround them. (Xinhua/Li Ying)