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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 a 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.