A leafhopper assassin bug (Zelus renardii) flips over a spotted cucumber beetle (Diabrotica undecimpunctata) to pierce underneath its protective elytra. Despite the common name, this assassin bug species feeds on a variety of insect prey. As young nymphs they primarily prey on aphids, thrips, and small beetle larvae, but by the time they are adults almost any appropriately-sized arthropod is incorporated into their diet. Changes in prey preference include more frequent predation on lacewing larvae, a fellow competitor that shares aphids as a food resource (termed intraguild predation). Because lacewings cause greater mortality rates for aphid populations, assassin bugs in high abundance contribute to increases in aphid herbivory (and can create problems for aphid biological control). When arthropod prey is scarce, Z. renardii is also known to consume plant tissues (phytophagy), which may be linked to its success as an invasive species in Europe.
Predatory strategies of assassin bugs differ depending on prey type. For quick and agile small prey, assassin bugs remain motionless, relying solely on an ambush. Larger and more slow-moving prey are instead stalked, with careful preparation for how to best grapple and stab the unlucky wanderers. Salivary enzymes injected through the proboscis are fast-acting and paralytic, completely subduing prey within a minute or two. Although assassin bugs (and hemipterans, broadly) may appear to have a rather unsophisticated method of feeding— just a stab and slurp— there is actually much more going on than meets the eye. Serrated mandibular stylets cut up the prey’s cuticle much like a pair of kitchen knives, and interior maxillary stylets deliver venom and digestive enzymes prior to ingestion of the liquified contents. While most predatory insects consume the entirety of their prey, reduviids are adept in extracting only the tissues of highest nutritional value, simply tossing away the chitinous husks.
Photographed in situ [1]; two-image focus stack