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Polysphinctini (20 species in the British Isles) are parasitic on spiders, both young and old. Many young Polysphinctini overwinter as larvae on the young spider host or in the hosts nest.
Most Polysphincta and other genera of spider parasitoids place the egg dorsally or laterally at the base of the spider abdomen, the host is temporarily paralyzed and the firmly fixed eggshell is utilized by the developing larva as a means of maintaining its attachment to the host body.
There are approximately 11 species in this genus.: P. atavina · P. boops · P. dizardi · P. gutfreundi · P. longa · P. mascoi · P. nielseni · P. purcelli · P. rufipes · P. tuberosa · P. vexator
Polysphincta tuberosa (Ichneumonidae: Pimplinae) is unusual in being a koinobiont ectoparasitoid - allowing the host to continue development but living outside the host's body. The adult lays a single egg on the front of a spider's abdomen - the host is often the common white & yellow/green spider Araniella cucurbitina. The position of the egg makes it impossible for the spider to remove it using its legs or mandibles and makes rubbing it off very difficult. When the egg hatches the larva stays in the same position and pierces the host's skin to drink its body fluids. In its first weeks the larva remains quite small (<=2mm) but this is because it is ticking over, waiting for the host to get big enough. Once it senses the host is the right size it will suck the spider dry over night and grow to 5-6mm in length! The larva then spins a silk cocoon and pupates - the adult hatching after a couple of weeks.
info from chrisraper.org.uk
