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Spider w/ parasititic larva? - Araneus diadematus

Spider w/ parasititic larva? - Araneus diadematus
Cowichan Valley, British Columbia, Canada
August 26, 2012
Size: ~4-5mm body length
Found and photographed in its web on a young Douglas-fir near the edge of the yard. My first time actually seeing a spider with a tiny parasitic larva attached! (I assume that's what's going on?)

I'm pretty confident the spider is one of the Araneus diadematus juveniles which are omnipresent around here right now, but is there any way to ID the larva? Unfortunately I was called away before I could take any close-ups of it, and the crop I've posted is pretty bad. If there's a possibility of getting somewhere with a higher quality shot, I can try to find the spider again tomorrow.

Larva here

Info Page
I've placed this image on the info page. Thanks.

Moved to A. diadematus
Moved from Spiders. Yes, I agree. I don't see a lot of parasitic larvae on these, so that's a nice find.

Moved from ID Request. Just thought I should get a second opinion on A. diadematus because the cross is missing..

Polysphincta larva…
The ichneumon wasp genus Polysphincta are parasitoids of many adult spiders, some of which even overwinter as larvae on the spider or in the spider's nest.

See reference here.

Very interesting. I imagine this spider would mature next year, so maybe the larva will overwinter with it, then. Thanks!

The spider is doomed, and at this time of the year I wouldn't be surprised if the larva takes only a couple more weeks to pupate (at which time it kills and eats the rest of the spider), though that depends on your climate.

Since the spider has no chance, you should capture it and keep it in a large container. It will go about its normal business of capturing and feeding on insects as the larva feeds on it. Right before the larva pupates it injects hormones into the spider which cause it to make an uncharacteristic tangled web in which the larva will hang as a pupa. After the web is built the larva kills and eats what it can of the spider, the then spins a cocoon around itself. If you keep it in the jar it will later emerge from the cocoon (in a week or two?) as an adult insect. At that time you can get pictures and post them to BG for an ID.

It's an interesting process to watch. I've done it with a few larva-parasitized spiders I've come across. The larvae I observed grew quickly.

Here is the adult wasp that developed from one of the larvae I was watching: