A few years ago Tim Manolis discovered in California that the jumping spider Sassacus vitis uses these translucent cavities as roosting sites and nurseries. The ultimate in green housing! He has since found two other species using dragonfly exuviae: Sitticus palustris and the ant-mimicking Peckhamia (near americana), although the latter may not be a regular user. It turns out that this behavior was known in Europe although it doesn’t appear that it has been investigated very thoroughly. Tim seems to be the only person in North America that is really looking into this and he would love to be informed if you find exuviae being used by jumping spiders (you can contact me and I’ll relay your information to him).
How can you tell when a dragonfly exuvia is being used by a jumping spider? The two that I have found so far I discovered by accident: I collected exuviae and then later found little jumping spiders wandering around the interior of the vials. A closer look at the exuviae revealed silk “tunnels” descending into the abdomen from the opening on the thorax.
Silk threads on the outside of the exuvia may be a clue, but I imagine some silk may be left by non-occupants just passing through too. You may be able to peer into the exuvia through the thoracic opening and see the silk-lined interior and a big pair of jumping spider eyes peering back (or at least glimpse some other body part). If you can’t see into the interior of the exuvia, try looking at it with a light source (the sun or a flashlight) shining from the other side like in the photo below. The dark blob in the abdomen is a jumping spider.
The photographed exuvia below—a Spiny Baskettail (Epitheca spinigera) at Lake of the Woods, was the second one that I’ve found with a jumping spider in residence. Like I said above, I only realized it after I noticed the spider wandering around in the vial that was holding the exuvia. After a short stroll it crawled back inside and that’s when I took the photo.
The first time I found a spider-occupied exuvia, it was that of a Four-spotted Skimmer (Libellula quadrimaculata) at Camas Prairie in the northern Oregon Cascades earlier this summer. I sent that occupant to Tim Manolis and he determined it to be Sitticus palustris. I’m hanging on to my latest find to see if tiny spiderlings emerge—it takes about three weeks for eggs to hatch according to Tim, and this spider seems to be spending a great deal of time in the exuvia as though it was guarding a clutch. Once I see whether “jumplets” are produced or not, I’ll send the adult to Tim so he can determine the species.
So, if you happen to come across dragonfly exuviae, see if you can find spiders within. Tim Manolis wants to know about them—especially from areas outside of Oregon and California since he currently only knows about spider-occupied exuviae from those two states. Information he is interested in includes the dragonfly species that left the exuvia behind and whether any spider eggs are inside (i.e. was the exuvia used for roosting or for nesting). If you can ship the adult spider to him he’ll be doubly appreciative and include the exuvia if you don’t know which species it is. If you don’t know how to reach Tim, contact me and I’ll put you in touch.
Thanks to Tim Manolis for providing lots of helpful information used in this post, and to the fine folks at BugGuide.net for their web site.
The spider eventually exited the exuvia and constructed a silk “hammock” in the vial. It turns out that it was a male using the the exuvia while molting. I sent the spider to Tim Manolis and it appears to be Sitticus palustris.