I know of no other single nectar source locally better than the long white blossoms of the Cali-fornia buckeye. It blooms from about the first week in May to the third week in June, differing greatly from site to site.

Observing buckeye trees on sunny days in Pine, Mitchell, Donner, Curry and Dan Cook Canyon was very productive. Binoculars are often necessary for seeing the butterflies (especially the hairstreaks) at the tops of these trees. The com-mon (chalcedon) checkerspot is often the most numerous butterfly on these blossoms. Some-times up to 200 individuals can be found on a single large tree! Other species you might en-counter on the California buckeye in the Mount Diablo area include: Mourning Cloak, Red Admi-ral, Lorquin's Admiral, California Sister, Northern Checkerspot, Editha Checkerspot, California Tortoiseshell, West Coast Lady, Painted Lady, Buckeye, Satyr Anglewing (more common at Las Trampas), Callippe Fritillary, Monarch, California Ringlet, Cabbage Butterfly, Alfalfa Butterfly, Large Marble, Great Copper, Echo Blue, and Acmon Blue, Gold-hunter's Hairstreak, Hedgerow Hair-streak, Dryope Hairstreak, Great Purple Hairstreak, California Hairstreak, the Farmer, Umber Skipper, Mournful Dusky-wing, Propertius Dusky-wing, Anise Swallowtail, Pale Swallowtail, Western Tiger Swallowtail, Two-tailed Swallowtail, Pipevine Swallowtail (more common at Las Trampas Wilderness) etc.

I often wonder if the nectar of this plant is different from other plants, for the butterflies at these blossoms seem unnaturally tame. I once had a California Sister crawl from a buckeye blossom to my fingers, where it perched for several seconds while trying to probe with its orange-colored tongue.This seemed unusual for a normally wary species. Perhaps the nectar has an intoxicating or narcotic effect as it is poisonous to bees.

When looking for butterflies, choose a sunny day with a temperature of 55° F or greater (usu-ally between 10 AM and 3 PM). Very few butter-flies fly when it is cool, foggy or rainy. A pair of binoculars is very useful, especially those that can focus 10' or closer. Collecting is prohibited at Mount Diablo State Park and all East Bay Regional Parks.

Other good nectar plants in spring for butterflies on Mount Diablo include Yerba Santa (per-haps the next best species after California Buckeye), Coyote Mint (excellent), Narrow-leaved Goldenbush, Yarrow, and Oregon Sunshine (Eriophylium lanatum). In the higher parts of Mount Diablo, where California Buckeye is rarely or never found, these plants can be particularly productive when searching for butterflies (especially for a number of rarer species).

At lower and middle elevations butterflies sometime seek nectar in spring at Brodiaea and its allies, Lu-pines, Milk Thistle (excellent) vari-ous yellow mustards (especially winter cress) and Mule Fat (Baccharis viminea). In summer and fall some of the best nectar sources include the blossoms of Toyon, Narrow-leaved Milkweed (excel-lent), Bull Thistle (excellent), Yellow Star Thistle, Hedge Mustard, Nude Buckwheat and Gum Plant (Grindelia Camporum).

Female butterflies often can be found if one knows the host plant for its eggs. For some butterflies, like the small-veined (mustard) white, the season is very short (spring only). It seems to prefer Milkmaids for both its host plant and as a nectar source.

Pipevine Swallowtail is rare away from its only host plant -Dutchman's Pipe (Aristolochia californica). In the Mount Diablo area this plant is probably only found at Diablo Foothills Regional Park. Callippe Fritillary's only host plants are violets and is somewhat restricted to their range.

Male butterflies of many species can be encountered at either hill-tops of at moist areas 0 soil or sand. "Hilltopping" and "puddling" in male butterflies appears to be re-lated to breeding activities. Swal-lowtail butterflies are the classic ex-ample of hilltopping butterflies where the males defend a territory. The summit of Mount Diablo is a good place to see the male Pale Swallowtail and Two-tailed Swal-lowtail. Puddling in butterflies is very widespread and usually in-volves newly hatched males.

On May 15, 1992, I hiked up Donner Canyon to Falls Trail. It was about 70 to 75 degrees at 12:10 P.M. when I reached where Donner Creek crosses the trail near an old bathtub. Along the edges of the creek and at an adjacent seep I saw an incredible gathering of mostly newly-hatched male butterflies. These included Two-tailed Swallow-tail (5) Pale Swallowtail (4) Echo Blue (20), Acmon Blue (1) Mylitta Crescent (1) Editha Checkerspot (1) Chalcedon Checkerspot (5), Califor-nia Sister (2) California Tortoiseshell (2) and The Farmer (60). When I returned around 3 or 3:30 P.M. most of these butterflies were gone. Most of these butterflies were easily approached and could have been photographed if only I had a camera.

Two handy books are California Butterflies (Garth and Tilden - UC Press) and A Field Guide To Western Butterflies (Tilden and Smith - Houghton Miffin Company).

This article appeared in Mountain News - Spring and Summer, 1993