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. 2023 Jul 10;120(29):e2305871120. doi: 10.1073/pnas.2305871120

Fig. 1.

Fig. 1.

Venom apparatus of asp caterpillars. (A) Megalopyge opercularis late instar. (B) Megalopyge crispata late instar. (C) Clusters of droplets of venom (blue arrow) harvested from the tips of spines with parafilm, showing a grid-like pattern. (D) Characteristic grid-like pattern of the lesion after natural envenomation by M. opercularis. Image by Dirk M. Elston (3) reproduced with permission. Panels E–I show scanning electron micrographs of an M. opercularis exuviae. (E) Cluster of venom spines (vs) among plumose hairs (ph). (Scale bar, 100 µm.) (F) Tips of two spines showing characteristic longitudinal striations. (Scale bar, 10 µm.) (G) Base of the venom spine (bvs) showing connection to the cuticle. (Scale bar, 50 µm.) (H) Venom spine broken near the tip showing trilobed cross-section due to longitudinal striations. (Scale bar, 25 µm.) (I) venom spine broken closer to base showing circular cross-section. (Scale bar, 50 µm.) Panels J–N show light micrographs of slices through formalin-fixed M. opercularis. (J) Longitudinal section through pigmented plumose hairs showing socketed connection at base. (Scale bar, 100 µm.) (K) Near-longitudinal section showing slender spine joining bulbous base or cone that merges with cuticle without a socket structure. Arrows indicate the transitional ring of the spine shaft where the cellular surround of the central lumen terminates. (Scale bar, 50 µm.) (L) Cross-section through venom spines and plumose hairs close to tips. (Scale bar, 100 µm.) (M) Cross-section through bases of plumose hairs (circled yellow) and venom spines (vs). “Dots” (orange arrow) indicate possible neuronal insertions. (Scale bar, 50 µm.) (N) Cell mass beneath scolus, showing canals (dark red circles) and large elongate secretory cells (gray circles). (Scale bar, 50 µm.) Panels O–R show µ-CT data. (O) Transverse slice through M. crispata late instar, showing canal-like structures through cuticle (blue arrows) and end-apparatuses of secretory cells (yellow arrows). (Scale bar, 1 mm.) (P) Three-dimensional reconstruction showing exocuticle with venom spines (red), endocuticle (green), and secretory cell end-apparatuses (yellow). Three spines have been labeled pink, their venom canals dark blue, and the secretory cell end-apparatuses they attach to light blue. (Q) View of three labeled spines within surrounding structures. (R) Closeup view of three labeled spines with surrounding structures.