Eggs on Coast Live Oak- Duskywing (Erynnis spp.) Eggs?

We found a couple of nice looking eggs on Coast Live Oak (Quercus agrifolia) today at Albany Hill, but are having a hard time identifying them! So far we suspect a duskywing species (Erynnis), but there are several in our region that specialize on oaks.

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Albany Hill is, without a question, Albany California's greatest landmark for wildlife. After all, the rest of the city is suburban; and yet, we have only investigated the place a few times since it is far from where we live. The few times that we have been there, we were collecting Western Tiger Swallowtails (Papilio rutulus). On those trips, we encountered several other lepidopteran species (well, butterflies since we have always gone in the day) such as the Common Buckeye (Junonia coenia), Monarch (Danaus plexippus), Mourning Cloak (Nymphalis antiopa), Red Admiral (Vanessa atalanta) and other Vanessas, Cabbage White (Pieris rapae), Umber Skipper (Poanes melane), Fiery Skipper (Hylephila phyleus), among quite a few other smaller butterflies (mostly nymphalids and lycaenids). 

Today, we decided to venture back to Albany Hill not with any of these particular species in mind; we would simply catch whatever we thought would be worth catching. Like many summer days in the East Bay, today was quite cool and cloudy, with the temperature in the mid 60's and humidity around 50% when we went out around 2 PM. This was not at all good weather to hunt for butterflies since most such diurnal insects are programmed to roost when day time weather is unfavorable like this, but there was a hint of sunlight earlier so we took our chances. When we arrived, we could not see a single flying insect in sight -- not one butterfly or even a damselfly which we saw dozens of on the other trips. It was a bad call.

Nonetheless, we stayed around just in case we should see something. We found a Monarch roosting in a tree that darted out when we came by because me must have startled it. We also caught a Fiery Skipper that we immediately released because we have no use of such a species. We actually spent the bulk of our stay investigating the vegetation for eggs or caterpillars. Since the part of Albany Hill we were at was bordering Cerrito Creek, it was an excellent riparian area dense with willow (Salix), a host of a ridiculous number of lepidopterans in our region including a few of those that we have encountered at the hill. Mixed in were also a lot of evergreen coast live oaks (Quercus agrifolia), a much less popular host due to its divergence from its deciduous relatives (the foliage of many evergreen species, such as coast live oak, have evolved to be heavily defended against damage). None of the species we have encountered utilize it.

As we were searching, we found a single very young oak tree growing on the creek bed. It was a small tree and was actually putting on a substantial amount of new growth for this time during the season probably because the creek provided the necessary water (none of the trees growing away from the creek had any new growth whatsoever). There were several new, dark pink shoot tips. But that was not what initially interested in this plant; when we had first stepped upon it, we noticed a few fungal growths that we originally mistook for eggs (alas!). These fungal growths were more or less spherical, had a slight mottled appearance, could be easily detached from the leaf, and closely resembled some kind of Saturniid ova. However, when we looked closer, we realized that they could not possibly be eggs because they came in all different sizes, presumably because the smaller ones grow into the larger ones. Moreover, breaking them open did not yield any distinct egg shell or yolk piece at all; it was the same material all the way through the entire structure and it felt slightly rubbery rather than containing fluid. 

As we were investigating these fungal growths, however, we noticed a bright yellow dot, conspicuously located on one of the pink new growths which would become the highlight of this trip. This time, it really was an egg, presumably lepidopteran. It was about the size of aVanessa egg, very spherical, and ribbed (shown below). Upon closer examination, we collected four more eggs, laid exclusively on the tender leaves of the new shoot tips. When we were leaving Albany Hill, we noticed another, much larger oak tree on the other side of the creek that was also putting on new growth and discovered two other eggs. One was blackened on one side and may be dead while the other one is a dark orange and is likely in a later developmental stage than the other bright yellow ones.

​As discussed above, the evergreen coast live oak is a terrible host plant for most insects and it was the last tree at Albany Hill that we expected to find any eggs on. To defend against herbivory, this particular variety has incredibly tough and dry leaves adorned with spikes and seems quite indigestible. No wonder whatever laid the eggs has a preference for the tender new growths!

Upon returning, we flipped through our Lepidoptera field guides and did some quick internet searches to identify the eggs. Statistically speaking, most Lepidoptera found in the wild are moths as they constitute the majority of the order, but in this case we suspect a butterfly because the eggs were laid singly and strictly on new outer growing shoots which just doesn't seem very moth like (moths tend to be much more careless about where they lay eggs). So, we first looked at true butterflies (Papilionoidea), and the only few species in our region that specialize on oak are the California Sister (Adelpha californica) and a few random hairstreaks (Lycaenidae). However, we have never seen any California Sisters on any of our trips to Albany Hill and their eggs barely resemble ours, and the hairstreaks are far too small to lay eggs the size of ours and their eggs don't resemble ours anyhow. So, next we moved on the skippers (Hesperioidea), and we quickly found two likely candidates in the Erynnis genus (Duskywings): the Propertius Duskywing (E. propertius) and the Mournful Duskywing (E. tristis). They are very similar species that both commonly utilize live oaks and lay their eggs on the newest shoots. A few quick internet searches showed us eggs that look very similar to ours, though it is difficult to say for sure because they're so small are hard to see. Anyways, for now our best bet is that the eggs are that one of these two Duskywing species, though if they really are we probably won't be able to tell which one it is until they are adults.

- Alan, Brian