I watched two presumed final instar caterpillars (on different plants), chew into the three main veins on the underside of a wood nettle (Laportea) leaf where they joined at the petiole and then actively drink the large clear fluid drop that quickly formed, held between the mouthparts and extended true legs. This caused the long thin leaf to very quickly droop and tent down over the caterpillar which then appeared to actively pull down on the leaf until it roofed over the caterpillar, when it began feeding from the basal edge of the leaf (all this while never changing its proleg foothold on the stem and petiole). I wonder what benefit balance this behavior might represent (hydration, gathering defensive chemicals or precursors, disarming leaf defenses, forming a camouflage shield?) Since the caterpillar clearly actively imbibed the fluid, it first seemed to me that toxics avoidance would be the weakest case unless, of course, the plant defenses would only be rallied upon wounding (unlike milky latexes that issue forth presumably already toxic?). In which case the larva might be wetting its whistle, disarming its opposition, and gaining shelter in one fell swoop.