Mystery Eggs on Mallow

9/10/2016

We have been finding what appear to be two kinds of eggs on wild mallow (Malva). At least one species involved is the Gray hairstreak (Strymon melinus); the other species could be the Common Checkered skipper (Pyrgus communis).

On 9/8, we found a fourth instar (mature) Gray hairstreak (Strymon melinus) caterpillar on wild mallow (Malva) in El Cerrito, CA. When we examined the particular plant more closely, we quickly realized that there were a series of eggs laid among it just by a glance. Most of them were already hatched with an obvious hole in the top where the caterpillar had exited, but we still managed to collect three fresh ones. We have found plenty of West Coast Lady (Vanessa annabella) caterpillars and eggs on mallow, their most preferred host plant in our region, which are easily recognizable, green, typical true nymphalid (Nymphalinae) shaped eggs and these were clearly not that.

What we initially assumed was that all of these new eggs were those of the Gray hairstreak since we had found the caterpillar. Gray hairstreaks are extremely common in our area (as well as elsewhere!) and we often see them around so it wasn't a big surprise that they are breeding here. However, upon taking a few photos of the eggs (yes, the quality of the photos isn't too great because our cheap camera has its limitations) two of the three (mystery egg 2) did not appear to resemble hairstreak (lycaenid) eggs exactly though they looked extremely similar. After quite a long time of investigating, we came to the conclusion that there were actually two different kinds of eggs.

Mystery egg 1

Mystery egg 2

Mystery egg 2 (refers to the white one; the green egg is that of the West Coast Lady [Vanessa annabella])

Mystery egg 2 zoomed in

Mystery egg 2 (refers to the white one; the green egg is that of the West Coast Lady [Vanessa annabella])

On 9/9, we collected three more fresh eggs, laid at a different location in Berkeley, CA, over a mile away from the ones that we found on 9/8. We have never monitored this site for butterflies. After taking a picture of these eggs, we again concluded that there were two different kinds of eggs (probably that same as the two kinds we found before, respectively). Unfortunately, we lost one of the eggs we found on 9/8 so we were down five eggs.

Mystery egg 1 is relatively flat, with a small greenish indent in the center; in our opinion, it looks like a fairly typical hairstreak (lycaenid) egg. They do not seem to be very firmly attached to the substrate. Mystery egg 2 is more spherical and has very obvious ridges, evident even in our poorly taken photos. They are more whitish or yellow in color. The eggs are about the same size as far as we can tell.

Mystery egg 1

Mystery egg 2

Today (9/10), one of the eggs that we found had hatched into what appears to be a Gray hairstreak. It is difficult to say for certain what kind of egg it came out of because there is a hole in it now and the details are vague but we think it was probably mystery egg 1, especially since mystery egg 1 looked more like a hairstreak egg. Coincidentally, while picking mallow leaves, we found another newborn Gray hairstreak without even knowing. We could not locate the hatched egg shell that this one came from. We also found five more eggs.

Because one of the two kinds of eggs has been confirmed to be that of the Gray hairstreak, the trouble now is figuring out the what else we have. Assuming that the newborn hatched out of mystery egg 1, our best guess for mystery egg 2 would be that of a skipper (Hesperiidae). Skipper eggs are typically spherical with the vertical ridges.

What really increased our suspicions today was that while we were looking for the eggs, we discovered Common Checkered skippers (Pyrgus communis) around the mallow. In fact, we even had the opportunity to catch one and it turned out to be a female. Of all the skippers commonly found in our region, Common Checkered skippers are the only one that we know of that feed on mallows as larvae. We shall see for sure once they hatch.

Newborn Gray Hairstreaks (Strymon melinus)

Hatched Gray Hairstreak egg

Mystery egg 1

Mystery egg 2

- Brian

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