Having landed on a (typical pea-like) flower, the syrphid is grasping the corolla "wings" (lower, outer petals) and preparing to probe with its proboscis for nectar or pollen within the slit along the upper edge of the "keel" (i.e. the two tightly appressed innermost petals, within which are hidden the stamens, pistil, and nectaries).

[Note: See this diagram if you're unfamiliar with the flower part terms used above. Overall the diagram would "read" better if they had flipped the cross-section of the keel "left-to-right" since, in reference to the flower profile at upper left, the ovary is attached to the base of the flower.]