The biologies of Zagrammosoma americanum Gir. and other small chalcid parasites are being studied at the Belleville laboratory. During these investigations a cage was required that would: (1) permit microscopic observation, with a minimum of disturbance to the insect, (2) allow ready introduction and removal of food and host material, without danger of the insects escaping, and (3) have aeration holes through which the interior could be sprayed. The description of a cage that satisfies the above requirements follows.