Caught a Female Papilio rutulus

Today we were relieved to find that the western tiger swallowtail (Papilio rutulus) that we caught is a female.​

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After capturing six male western tiger swallowtails (Papilio rutulus) at Albany Hill since last summer and witnessing a number of others exhibiting characteristic "male-like" patrolling behavior,  we were starting to really lose hope that we would ever be able to locate a gravid female. Of course, in the past we have consistently witnessed what were or could have been females flying in the city area as close as our backyard, but these were always chance occurrences that we could not have been prepared for. What we really just needed was to discover some place that was popular to female swallowtails, or at least to both sexes (not exclusively male like the hill),  so that we could come prepared on a designated day with net and other equipment. 

​Yesterday afternoon after what at first seemed to be another one of these odd chance occurrences, we suddenly began to get clued in that the section of Cerrito Creek along the bay trail blocks before Albany Hill might just be this type of female heavy location. At about 5:30 or so, having just come from the post office with absolutely no field equipment or even a bag, we witnessed what we were positive was a female Papilio rutulus fly out from deep within the willow (Salix)  thickets and land extremely calmly on a nearby tree. Our basis for this classification on the absurd amount of blue lining on the hindwings that was practically nonexistent on any male we have ever encountered. It also caught us off guard at how the butterfly was so incredibly tame, sitting in its resting spot, unlike a patrolling male that only ever lands for a sip of nectar. Unfortunately, even after using a hooded jacket as a makeshift butterfly net, we weren't able to capture this one (although we did manage to pin it to the ground for a few seconds before it came to its senses and dashed away). 

Coupled with the fact that we had actually found a Papilio rutulus egg along this section of Cerrito Creek less then a week before this observance, it was becoming more and more clear that this was a place, despite being surrounded by tall buildings and a busy shopping plaza, was an established habitat for the species. And from what we have encountered thus far, it is only logical to say that it is this place that is frequented by gravid females and not males whereas at Albany Hill it seems to be precisely the other way around. One is a distinct breeding ground while the other is a distinct mating ground where males gather and virgin females know to visit once before heading out and actively avoiding such grounds where they run the risk of getting harassed.

We basically confirmed this when we went out to the same spot today during the peak of the afternoon (3 PM) and found what was clearly a different, second female fly out from what was vaguely the direction of Albany Hill and into the willows of the creek before landing on some type of conifer. Exactly like the previous individual, this female was extremely tame on the tree and probably would have stayed there for a while if we didn't immediately nab it with our net, which (thankfully) we had brought with us this time. 

This female evidently has some age considering that its layers of scales appear thin (it does seem to be a rather pale individual to begin with though, typical of the spring brood), it was losing a tale even before we caught it, and its abdomen is a bit skinny. It has most likely already laid some eggs in its lifetime which, when trying to get butterflies to lay in captivity is highly advantageous because you don't have to wait for a number of things to happen. Just based on past experience, wild-caught females butterflies that have already been laying eggs in the wild (often they are captured while in the act!) are usually very cooperative in captivity unlike freshly paired captive raised females. Therefore, we do hope that we are able to get this female to oviposit on willow cuttings once we have the cage set up by tomorrow afternoon. Already a hot sunny day today, it is supposed even hotter tomorrow and this coming week due to winds blowing east from inland which should help tremendously in our efforts. 

Authors
Brian Liang

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