From Destinypedia, the Destiny wiki
Supplicants are a unique variant of Vex Harpy with the ability to self-destruct, first appearing in the Vault of Glass Raid. They return in the expansion Shadowkeep, where they were employed by the Sol Divisive during the Garden of Salvation Raid and the Vex Offensive. Supplicants, once again, make a return during Season of the Splicer in the reworked Vault of Glass raid, but this time being employed by the Sol Collective.
Supplicants typically appear in groups, and their primary method of attack is to quickly fly up to their target and damage them by exploding when they get too close. In the Vault of Glass, Atheon, Time's Conflux will summon them in groups of three whenever it goes into stasis. In the Garden of Salvation raid, Supplicants will spawn from the side pathways during the third encounter. It is recommended that they be eliminated as quickly as possible when they spawn.
List of appearances