Sunny Day with Butterflies and Bees in Sutro Forest

One of the lovely things about Mount Sutro Forest is its changing moods. We posted pictures here of a foggy day recently, when the forest was ethereal and damp. But the previous afternoon, it was sunny in the forest. A perfect day for butterflies and bees.

We’ve seen bees working the blackberry bushes in the forest before, but this time they were so intent on their food gathering they let us get close and get photographs.

bee on blackberry flowers sutro forest 2So here it is, busy as a bee… of course.

bee on blackberry flowers sutro forestflowering_gum with bees susan walterWe know bees also forage on eucalyptus flowers, especially when other plants stop blooming.

Our trees are so tall that we haven’t yet succeeded in getting the photograph, but other photographers have.

In fact, someone recently sent us a link to the Israeli paper Haaretz, which report that in Israel, bee-keepers were able to save eucalyptus trees slated for removal. There, too, eucalyptus is a crucial source of sustenance for bees.


We were delighted to find quite a few gorgeous Anise Swallowtail butterflies – half a dozen or so.  They’re not common on Mount Sutro. This butterfly lays its eggs on fennel, which is unfortunately one of the plants the Natural Areas Program targets with its toxic pesticides.

anise swallowtail

On Mount Sutro – at least, UCSF’s portion of it – no pesticides are in use, but there’s no fennel either. These butterflies will have to hunt for other places to breed.

anise swallowtail body


Then we saw something we had never seen before. In a sunny patch, two Anise Swallowtails were flitting around. Eventually, one stayed and the other left. An Umber Skipper, a  little brown butterfly maybe a quarter of its size, started chasing the remaining Anise Swallowtail. It looked like a blackbird harassing a hawk, using its superior maneuverability. Eventually both of them settled on a twig, and we got this picture.

two butterflies - umber skipper and anise swallowtailWhat was happening, we wondered? We asked Professor Art Shapiro of UC Davis, an expert on California butterflies. Here’s what he said:

“In riparian habitat, both species use sunflecks as sexual rendezvous sites. (Anise Swallowtails also use hilltops in hilly terrain. Umbers don’t.)  Males and mateable females (generally virgins) are genetically programmed to find such places–butterfly “singles bars.” Both of these critters are males. Presumably the presence of the swallowtail in the same fleck might have deterred a female Umber from approaching; or perhaps it was a purely mechanical response to movement nearby; in any case it was almost certainly a direct or indirect example of interference competition for a limited resource–a sunfleck. Great picture!”

Who knew butterflies did that? They seem so pretty and so mindless  – but like all other creatures, they’re busy trying to survive and reproduce. Umber skippers breed on grass, including Bermuda grass. So if this one succeeds in finding a mate, they should be all set.


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2 Responses to Sunny Day with Butterflies and Bees in Sutro Forest

  1. milliontrees says:

    We recently visited Albany Hill to check on the eucalyptus forest because Jake Sigg claimed the trees there are dying of drought. We saw pairs of Anise swallowtail butterflies circling one another and briefly “connecting” in a sunny spot we now know to be a sunfleck. Interesting word. I wonder if it is derived from the word lek, which is used to describe the places where some bird species perform elaborate rituals to attract their mates.

    By the way, the eucalyptus forest on Albany Hill looks fine. We compared pictures of it with pictures we took two years ago at the same time of year. We couldn’t see any significant difference.

  2. Jacquie says:

    Great pictures and observations!

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