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Hi. I've found a possible black wasps in my back garden today and looks like it could be nesting under 1 of the flag stones, i only noticed it after seeing something out of corner of my eye an when I got closer, it lookd like it had stung and paralysed a spider which it was dragging into its nest. I managed to catch the wasps in a plastic container so I could take a couple of pics cos never seen or heard about any before in this country until today. I've released it back into the garden but is it safe to leave in garden or should I try to catch again an try re-locating it?

As mentioned earlier in this thread, it's nigh on impossible to clearly identify without some close up observation. However, most adult wasps are, I think, nectar eaters using "livestock" to feed their larvae.

This came from Wikipedia

Spider wasps are solitary wasps that use a single spider as a host for feeding their larvae. They paralyze the spider with a venomous stinger. Once paralyzed, the spider is dragged to where a nest will be built – some wasps having already made a nest.

Wasps can sting, so I suppose you need to weigh up the pros and cons. If you've got kids that might get stung it might be necessary to remove it. It would seem that these wasps need quite a hefty sting to stop a spider and so stings can be quite painful.

Or it may go by itself. By all accounts they're solitary creatures, so having done its job getting food for the next generation it may have already flown away. You then need to decide what to do with that.

If you can give it some distance, it might be really interesting to watch.