Greek mythology has it that the lesser deity Zelus, who, with his brother Nike, stood by Zeus’ side and enforced his edicts, embodied the traits of envy, jealousy, and zeal. While watching assassin bugs, one has to admire and perhaps even envy their stealth and cunning in stalking and capturing prey. Witness the mighty assassin bug known as the wheel bug as it dispatches a hapless caterpillar:
After sizing up its prey, the wheel bug strikes with astonishing speed.
Not all assassin bugs rely on sheer power to subdue their victims. In a previous episode we met the milkweed assassin bug Zelus longipes. Hiding motionless in a flower-head or slowly moving about a leaf, it employs hairs on its front legs known as sundew setae to snare its prey. Specialized glands produce a highly viscous and sticky substance that coats these specialized hairs. Should small prey items like flies or wasps that might otherwise escape unharmed make contact with a clutching foreleg, they may become stuck in this gummy secretion and cannot escape. Once captured, the prey is impaled with a hungry beak that injects proteolytic enzymes, predigesting the contents of the victim. The liquefied contents of the prey are sucked into the digestive tract of the assassin bug with the aid of a tiny muscular pump in the assassin bug’s head.
Older Zelus nymphs and adults are able to produce the sticky goo used to capture prey but a clever study demonstrated that hatchling nymphs lacked the sticky droplets used to snare prey. However, mother Zelus is a good provider. When she deposits her eggs on the surface of a leaf, she leaves behind a coating of viscous fluid on each egg. One of the first tasks undertaken by the hatchling nymphs is to gather the sticky fluid and spread it onto their legs. Armed with an innate calling to capture prey and sticky legs to seal the deal, young Zelus embark on a life of predation amongst the flowers and foliage in the garden.
Zelus nymphs hatch from barrel-shaped eggs deposited by their mother. Watch closely as hatchlings dab the egg mass with their legs to collect the sticky fluid used to help them capture prey.
Tiny predators with sticky legs evoke awe in me.
Bug of the Week thanks Rebeccah Waterworth for providing Zelus eggs, video and images used in this episode and for the inspiration behind this story. The fascinating article “Observations on the sticky trap predator Zelus luridus STÅL (Heteroptera,Reduviidae, Harpactorinae), with the description of a novel gland associated with the female genitalia” by C. Weirauch provided insight into the nature of this zealous predator.