"Nature Abhors a Vacuum"

Long-Jawed Spider and Common Green Darner Exuviae, July 17, 2021

As part of my study of the Homer Lake Wetland dragonfly population this year I have been collecting the shed exoskeletons ("exuviae") left behind by the adult dragonflies that emerge from the wetland. These are useful both as rough indicators of the numbers of dragonflies emerging as well as the species of dragonflies successfully emerging. Interestingly, as in the photo above, there are often spiders hanging around or even possibly inside some of the exuviae I collect. In almost all cases there is no evidence that the dragonfly was preyed upon by the spider -- the exuviae is empty and there is no sign of the adult dragonfly, so it seems that it emerged successfully and finished its process and flew off -- though there are a couple of exceptions. No, in most cases it seems that the spiders hanging around the exuviae are either there coincidentally or else they are interested in the empty exuviae itself. In the case of the long-jawed spiders, as in the photo above, I suspect that the presence of the spider near the exuviae is purely coincidental. These spiders are very common in the wetland so one occasionally ending up near an exuviae is to be expected.

In other cases, however, it seems likely that the spiders are actually intending to or in the process of making use of the empty exuviae as a place to hide out. There has, in fact, been research done on jumping spiders in California using dragonfly exuviae (paper here). My observations are mostly anecdotal but occur with enough frequency that there certainly seems to be more than a random connection for some of these spider species. Below are photos of some of my observations with comments included under each. All photos are from the Homer Lake Wetland and taken this Summer.

This common green darner exuviae has had its grip on this arrowhead leaf reinforced with spider web. It appears that a spider had an interest in making sure this exuviae did not fall off of the leaf. The exuviae itself was empty indicating that the adult dragonfly had exited successfully, so this was not a case of the immature naiad being attacked and bound by web. 

I make my way around the wetland two or three times a week to collect exuviae in a plastic bucket. I often subsequently find spiders in the bucket or the exuviae stuck together with spider web which wasn't there when I collected them. Either the spiders were on the exuviae and I put them in the bucket without noticing them and without them jumping off or they were INSIDE the empty exuviae when I collected it and came out after the exuviae was in the bucket. Pictured above are two different spiders that showed up in the bucket on August 18 along with some darner exuviae pieces (they sometimes come apart when removing them from the plants). The exuviae are plenty big enough for either of these spiders to take refuge inside.

Another "stow-away" spider found in my collection bucket on August 21. Like the spider on the right in the photo above, this spider appears to be a young six-spotted fishing spider. As noted in the blog post on six-spotted fishing spiders, these spiders are quite common at the wetland and other local bodies of water (and they are so-named for six spots on the underside, not the spots on top of the abdomen, which number more than six!) 

A pretty little jumping spider I found in the collection bucket on August 22, one day after collecting exuviae (and the day after I found the spider above in the bucket). It seems most likely that I collected this spider inside an exuviae the same day I collected the spider in the photo above this one, but this one took longer to come out of hiding.

On the abdomen of this common green darner exuviae found August 27, 2021, just beneath the joint in the hind leg is a young six-spotted fishing spider (click photo to view larger). If my hypothesis is correct, it may have been exploring for an entrance into the exuviae or perhaps the whole process is more serendipitous: maybe the young spiders come across exuviae as they are hunting and happen to find the openings and take advantage of them as hiding places. 

A larger six-spotted fishing spider acting rather possessive of a saddlebags exuviae on the underside of an arrowhead leaf at the wetland, September 3, 2021. On this same day I also found another six-spotted fishing spider holding onto a darner exuviae. In both cases I had to (gently) convince the spiders to leave in order to collect the exuviae for the research I am doing.