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Hi,
Yesterday I saw this young Araneus diadematus spider in my garden. I took a photograph because of its nice colours and then noticed a yellow "swelling" on the side of its abdomen that is obviously a larva. I know Pompilid wasps burying paralyzed spiders with an added egg, but I did not know that unburied lively spiders can be attacked by parasitic larvae. Which insects can be such parasites?
Thanks for any information, Sundew

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it is probably an Ichneumonoidea wasp.

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Pompilidae wasps only paralyze them... and then they give the spider to their larvae... and the spider is ate alive (it is like a dead-alive)...
Sphecidae wasps predate on spiders, for example. And Ichneumonoidea wasps parasite the spiders.
In diptera, only the famous Acroceridae flies parasite them. Acrocerids are really true ENDOparasitoids of spiders.

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Reminds me of a polysphinctine pimplid larva, but the ones I have seen were always on the anterodorsal part of the abdomen. Nice photos