Moth Night at Skyline Gardens – June 2019

This past month has been full of scouring hill and dale to keep ahead of Italian Thistles and Wild Oats, and we’ve done a great job of that with our thistlecatchers and our mowing. Although we’ve just entered Summer, for the next month we are still weeding to catch such invaders as Rose Clover, Scattergrass, and Spurge before they ripen and throw their seeds. This will save us tons of work come the rains. As to wildflowers, right now the Sticky Monkey and Farewell to Spring are just glorious, as are the big, red Cobweb Thistles. Soap Root flowers, literally by the thousands, open fresh each day as dusk approaches.

Speaking of evenings, in May, we did an early season Moth Night to wrap up our UC Berkeley DeCal class. Moth nights are best on warm, still evenings. We got the opposite – a cold, foggy, windy one. We set up our sheets and UV lights in the lee of the wind in three places along the Skyline Trail between Steam Trains and the old bench at Siesta Nose.

We were visited by over fifteen moth species, but curiously, these were almost all large moths. We guessed this was because the larger ones are stronger fliers and better able to navigate tough moth conditions. The smaller ones were just not out (or able to find us) in the fog and the wind.

Tetracis cervinaria Geometrid
Tetracis cervinaria Geometrid. Photo by Ken-ichi Ueda.

Several beautiful ones did find us. First, here is one of the Geometrid moths:This one, Tetracis cevinaria, is about two inches across. The golden wings are highlighted by a purple stripe. They are native to western North America. As far as we know, this one does not yet have a common name, but the caterpillars feed on native Prunus species. 

Next we have the Vestal Tiger Moth (Spilosome vestalis). These are pure, snow white and fuzzy. Vestal Tiger Moths live on the West Coast of North America, mostly in dense forests. One of their larval food plants is Alders, and there are many Alders growing along the banks of Siesta Creek, down in the valley.

 
Vestal Tiger Moth. Photo by Ken-ichi Ueda.
Tiger Moth
Tiger Moth. Photo by Cat Chang.

These moths have black spots on their abdomens, but most strikingly, they have a boss of bright scarlet fuzz on each front fore-leg. Here’s a close up of that. The black dots on the abdomen and the scarlet fore-legs are diagnostic for this species.

Towards the end of the evening, we were visited by one, large Sphinx Moth, also known as Hawk Moths or Hummingbird Moths. These are very large moths, sometimes mistaken for Hummingbirds. They resemble Hummingbirds in their flight patterns, as they hover over flowers while nectaring. This one, the White-lined Sphinx Moth (Hyles lineata) is nearly three inches from head to tail, and makes quite a sound. They occur all across North America.

White-lined Sphinx Moth (Hyles lineata)
White-lined Sphinx Moth (Hyles lineata). Photo by Ken-ichi Ueda.
Sphinx moth on thistle
Sphinx moth on thistle. Photo by Greg Lasley via iNaturalist.

They are known as “long-tongued nectar foragers.” The very long “tongue” is used for feeding from large thistles and Evening Primrose flowers, among others. Here’s a Sphinx Moth in action, hovering above a big thistle flower head, and you can see the long tongue inserted deep inside. This photo is from iNaturalist, taken in the Hill Country west of Austin, Texas, and we thank Greg Lasley for a great shot. I’m not sure of this thistle species, perhaps a native Texas one, but I’m willing to bet that these moths also feed on our giant, red Cobweb Thistles up on the ridge at Skyline Gardens.

Hawkmoth caterpillar
Hawkmoth caterpillar. Photo by Eric Wrubel.

Although I’ve seen Sphinx Moths elsewhere, I did not know they occurred in lowland California. The mystery was deepened by hearing that their larval food plants are primarily in the Evening Primrose family. Somehow, I could not imagine enough Clarkia, Epilobium, or California Fuchsia to sustain them in our local area.

Then, last week, a group of us were down in Siesta Valley looking at Sedges (Carex) and since these are mostly water-loving, we visited Siesta Springs along the De La Veaga Trail. Eric Wrubel, a Carex expert who works for National Parks over in Marin, was our Carex guide for the day. Lo and behold, he spotted this whopper caterpillar on a stem of a water-loving species of Epilobium, probably E. ciliatum, which grows very profusely at the springs. Look at the size of this one, as big or bigger than your pinkie finger! (Thanks, Eric, for the find and the photo.)

Of course, it all makes sense now, mystery solved; one more link in the web of life.

Glen Schneider