Kleptoparasite

This morning was a good time for insect photography–it was chilly enough that a lot of things that normally would have jumped, flown, or scurried away were sluggish enough that they let me get my lens right in their faces and take as many shots as I wanted until I was satisfied with the results.  A few examples:

This 5 mm-long moth is a member of the genus Caloptilia (Gracillariidae).  There are over 60 species in North America, and as larvae they typically start out as leafminers and then exit the leaf, completing their development in a cone-shaped roll they create at the edge of the leaf.  I’m not sure which one this is, though to my eye it looks similar to C. rhoifoliella, which feeds on sumac.  I’ve always gotten a kick out of the upright, dignified-looking posture of these moths, and this is the first one I’ve seen in person (besides the one I found in my friends’ kitchen last week).  This second shot better shows the stylish frills on its front legs, as well as the outrageously long antennae that it would alternately tuck back along its wings (as shown above) and swing about in the air.

I found a harvestman resting perfectly still on a tree trunk…

…and was impressed by all the little spikes I found when I zoomed in on its face:

Joe Warfel tells me it’s an Odiellus pictus (Phalangiidae).  Nearby, a beautiful sheetweb spider (Linyphiidae: Drapetisca alteranda) was slowly devouring an aphid:

This leafhopper (Cicadellidae: Coelidia olitoria) had a nice color scheme:

…And then I came to this spider web.  This is one that is distinctive enough to identify to species without looking at the spider itself: the filmy dome spider (Linyphiidae: Neriene radiata), named for the dome-shaped sheet in the middle of its web.  The spider hangs upside-down from the top of the dome, waiting for flying insects to get caught up in the maze of threads above it, and when they make their way down to the top of the dome, the spider grabs them.

Except the spider in this web was not a filmy dome spider.

It was a kleptoparasitic cobweb spider (Theridiidae: Argyrodinae), which makes its living by wandering into the webs of other spiders–in some cases spinning its own little web there–and stealing the prey caught in the other spiders’ webs.  In cases where the other spider is substantially larger, I suspect the cobweb spider (less than 3 mm long) is mostly taking insects that are too small to be of interest to it.  Several times this year I have seen these little spiders wandering around in the periphery of orbweavers’ webs, but this is the first time I’ve seen one in another type of web.  It’s also the first time I can remember seeing an unoccupied filmy dome spider web.  These webs are elaborate structures that are inhabited by their makers indefinitely, so it wouldn’t make sense for the spider to put all that time into spinning the web and then just wander off.  I looked around a little and spotted the spider resting on a twig nearby–it’s actually partially visible in the bottom right corner of the shot of the web.

I’m not sure why it would be outside its web.  Maybe it figured it was too cold and windy to catch any bugs anyway, and it might as well hang out somewhere where it was less obvious to predators, so it left its guest to be blown around in the breeze.

About Charley Eiseman

I am a freelance naturalist, endlessly fascinated by the interconnections of all the living and nonliving things around me. I am the lead author of Tracks & Sign of Insects and Other Invertebrates (Stackpole Books, 2010), and continue to collect photographs and information on this subject. These days I am especially drawn to galls, leaf mines, and other plant-insect interactions.
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5 Responses to Kleptoparasite

  1. Dave says:

    I’ve seen members of the Argyrodinae eating their hosts, even when the host spider was much larger than them, so maybe the filmy dome spider is hiding from the klepto. As I recall, pretty much the full range of spider harassing behaviours occur in the Argyrodinae from wandering spider predators to full-time silk and small prey thieves and many of the latter aren’t above eating the hosts if it is convenient. I can remember watching one that had been inhabiting a tent spiderweb (Cyrtophora moluccensis – their webs are very large and last for months) for a week or so and then eating the host when it was halfway through a moult.

  2. Nick says:

    Great macro shots!

  3. Lynne Kelly says:

    Fascinating blog, wonderful photos and really interesting observations. Thanks also to Dave for his reply. Love this blog!

  4. Pingback: A Winter Visitor | BugTracks

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