The video above shows how aphids defend themselves against ladybird beetle larvae (and presumably other predators) by secreting glue-like droplets:
As the ladybird approaches, aphids pour out of the gall and grab the predator by their jaws and legs. It’s a suicide defence. The aphids secrete massive amounts of waxy liquid from their bodies, which quickly solidifies and glues the ladybird to the plant. Unable to walk or bite, the ladybird dies and the aphids go with it.Found at Not Exactly Rocket Science, which has more details (and congratulations to that blog for winning the "Top Quark" award for best science writing in 2010.