Eggs, caterpillars, pupa, and adult of Phryganidia californica.
The California oakworm or oak moth (Phryganidia californica), returned to the UC Berkeley campus for the second year in a row.
In June 2019 the Essig Museum received a call from a reporter at the Daily Cal asking about moths flying around oak trees on campus. Normally people do not notice the moths, but they certainly notice the onslaught of caterpillars eating the leaves of coast live oaks (Quercus agrifolia), and occasionally other oak species. By August many trees on campus were stripped bare. But by the end of October they recovered. In May-June 2020 we are witnessing the return of the oak moth.
The same tree at Sproul Hall: defoliated (August 15, 2019), recovered (October 3, 2019)
Oak moths typically have two generations per year – one in the spring and one in the fall. As of June 2020 we are seeing the spring caterpillars emerge as adult moths and laying eggs. These eggs will turn into caterpillars that will continue to defoliate trees in August and September. The caterpillars seem to focus on individual trees, rather than attacking all trees equally. This probably has to do with where the females lay their eggs, but the defensive chemistry of the oak trees may play some role.
This chemistry may also play a role in protecting the caterpillars and moths from birds and other predators. Many non-toxic moths and caterpillars hide during the day and feed at night. But oak moths and their caterpillars are very active during the day and do not seem to attract flocks of birds. Their main predators seem to be parasitoid wasps.
Feeding damage by Phryganidia caterpillars.
Once finished feeding on a tree, the caterpillars lower themselves by silk threads that can blow them to another tree to continue feeding, or two the ground where they will wander in search of a place to pupate. In nature these caterpillars would find a crack in the tree bark or side of a rock to anchor their pupal case (which looks more like a butterfly chrysalis). On campus these caterpillars can form masses on the sides of buildings, and sometimes crawl into utility access tubes.
Masses of caterpillars at Campbell Hall in August 2019.
As if the oak trees are not suffering enough, this year is looking like a big year for tussock moths as well. Females of the western tussock moth are flightless and crawl a short distance from their cocoon to lay large masses of eggs. Caterpillars have distinctive tufts of white or cream hairs that can sometimes irritate skin.
Tussock moth caterpillar and cocoons on coast live oak.
Have you ever touched the wings of a moth or butterfly and gotten some “powder” on your fingers? That powder is actually tiny scales, like on a fish or lizard, or like the feathers of a bird. These scales give butterflies and moths their scientific name Lepidoptera (from the Greek Lepido = scale, and ptera = wing). Each scale can be a different color and when placed next to each other, the mosaic makes up the color patterns we see. Some are brightly colored to warn that this species does not taste good (aposematism), or look like distasteful species (Batesian mimicry), while others look like eye spots to startle predators (image to the left), and still others form a camouflage pattern to blend in with their background.
Most colors are caused by pigments that form inside the individual scales and reflect light through holes on the scale surface (image to the right), while others, especially blues, are structural and result from light refracting off of ridged surfaces, like looking at the underside of a DVD. For more information on how blue (structural) colors are formed on butterflies watch KQED’s Deep Look episode “
Edward S. Ross (1915-2016) was a pioneer of close up photography. Ed received his PhD in 1941 with the Department of Entomology at UC Berkeley, where he was a teaching assist for E.O. Essig. Before finishing his degree he was offered the position of Curator of Entomology at the California Academy of Sciences in San Francisco in 1939, and two years later became chair of the entomology department, a position he held for 41 years. Initially Ed was interested in Histerid beetles, but soon switched to webspinners (Embiidina), a group for which little was known at the time. His studies took him around the world, particularly to the tropics where webspinners are most diverse. During his travels Ed photographed arthropods, plants, mammals, people, and natural landscapes. His images appeared in numerous publications including National Geographic Magazine, Insects Close Up, and Insects and Plants. In 2018, Ed’s collection of ~100,000 35mm slides were generously donated to the Essig Museum of Entomology by his wife, Sandra Miller Ross, to be digitized and made available for research, education, and outreach. Once digitized, the images will be available through 
Ride, walk, or jog along the 
You have probably noticed a lot of these critters around town lately; they seem to be just about everywhere this time of year. These eye-catching little beasts go by many names, including “Cross Orb-Weaver,” “European Garden Spider,” and “Pumpkin Spider,” among others,1,2 but their proper scientific name is Araneus diadematus. (Note: common names like “Garden Spider” or “Pumpkin Spider” may refer to a number of different spider species, which is understandable given that there are an estimated 47,000 (or more)3 spider species on earth! Since we have not come up with 47,000 unique common names for all of these species, it is best to use scientific names to avoid confusion.)
not to hurt large vertebrates like us. And while a bite from one of these guys might be painful and cause a small localized reaction8 (much like a bee sting), the chances of being bitten are so slim that it is a non-issue. These spiders are not the least bit aggressive; they like to keep to their webs and mind their own business, and would only bite as a last resort (i.e. if they were about to be squished). So next time you walk through a huge web that a resident A. diadematus thoughtfully constructed right in front of your door, do not panic – the spider is running for the hills as we speak. If you are lucky, your little 8-legged buddy might stumble into your hands and let you take a closer look!
