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The hymenopteran family Scelionidae is a very large cosmopolitan group (over 3000 described species in some 160 genera) of exclusively parasitoid wasps, mostly small (0.5-10 mm), often black, often highly sculptured, with (typically) elbowed antennae that have an 9- or 10-segmented flagellum. Nowadays, it is considered to be a subfamily of Platygastridae.
They are generally idiobionts, attacking the eggs of many different types of insects or spiders, and many are important in biological control. Several genera are wingless, and a few attack aquatic insect eggs underwater.