He was my host he was my guest — Gall Fly

He was my host-he was my guest, 1
I never to this day
If I invited him could tell,
Or he invited me.

So infinite our intercourse 5
So intimate, indeed,
Analysis as capsule seemed
To keeper of the seed.
(F.1754/J.1721)
[1] He, guest:: a guest-fly, or gall-fly, an inquiline. Gall-fly will make galls on plants for breeding. host, guest:: two gall-flies shared a gall; they can be both guest and host.
[2] I:: a gall-fly.
[7] capsule:: the gall looks like a pod.
[8] keeper, seed:: the gall is their breeding pod.

These larve inhabited elongate, pod-like galls, formed on the ends of the branches of the Pistacia terebinthus. These galls contained many hundred Aphides, and appeared to be formed by those insects. . . . "other insects which habitually breed in the galls formed by the true gall-makers, and which, as they feed on the substance of the gall itself, and only occasionally or incidentally destroy the gall-making insect, may be appropriately considered as Inquilines or Guest-flies." ─ The Entomologist's Annual, Volume 13 (1867)