Bug Day (8) Checkerspot

This post inaugurates Bug Week on chavezpark.org. Unless other matters interrupt the schedule, you will see:

  • Bug Day (8) Checkerspot today
  • Bug Day (9) Sandhill Skipper June 24
  • Bug Day (10) Checkered Skipper June 25
  • Bug Day (11) Miserable Mining Bee June 26
  • Bug Day (12) Jumping Spider June 27
  • Bug Day (13) Warrior Grasshopper June 28
  • Bug Day (14) Potato Mirid June 29
  • Bug Day (15) Black-tailed Bumblebee June 30
  • Bug Day (16) Checkered Beetle July 1
  • Bug Day (17) Aphids and Ladybug July 2
Variable Checkerspot (Euphydryas chalcedona)

The Variable Checkerspot (Euphydryas chalcedona), also known as Chalcedon Checkerspot, is a West Coast native engaged in a chemical arms race with the plants it feeds on and the birds that feed on it. In order to make itself unattractive as bird food, its larvae feed on plants that are rich in catalpol, a compound that tastes nasty to birds. However, many of those same plants produce a phenolic resin containing formaldehyde that is repulsive to checkerspot larvae and reduces their growth and survival chances. The plants manage to concentrate the resin in their newer, greener leaves, which the larvae prefer. The larvae that feed on the older, drier leaves avoid the poison but get inferior nutrition. And so it goes. However, in Cesar Chavez Park, we haven’t so far located the well-defended host plant Diplacus aurantiacus (Sticky Monkeyflower) that the checkerspot usually favors. We do have this butterfly’s Plan B, the California Bee Plant (Scrophularia californica), where the larvae can feed without encountering formaldehyde, where catalpol is present, and where the adult’s only food source, nectar, is abundant.

The checkerspot’s sex life begins when males find a cluster of females, usually near nectar-rich plants. The male doesn’t engage in any special courtship display. He chases the female and attempts to curl his abdomen forward and insert it between the female’s hindwings. If she holds still for this, copulation begins, and the pair may stay locked together for an hour or more. The male injects the female with a compound containing his sperm plus a rich complex of nutrients that represents about seven percent of the male’s body weight. He also injects a plug that hardens in a few hours, preventing additional males from inseminating the female. But females quickly seek another mate and may hold the sperm packages of many males, with only the most recent one fertilizing her eggs. Fortunately she has a second genital opening through which she ejects her eggs. She quickly deposits clusters of her eggs on the chosen host plant. The larvae remain dormant during the winter — sometimes for several years — and develop into butterflies in the spring. Life expectancy of adult checkerspots is about 15 days. Carpe diem.

This native species is closely related to the federally threatened Bay Checkerspot butterfly, which used to be abundant in the hills around San Francisco Bay. The Variable (or Chalcedon) butterfly photographed (above) at Cesar Chavez Park is the only member of the Checkerspot genus reported here. Perhaps with more native planting, more Checkerspots of all kinds will make their homes in the park.

More about them: Wikipedia

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