Biting behavior of beneficial beetles: Quantification of coccinellids

The tendency of aphidophagous coccinellids to bite humans is a subject that has seen little study in the scientific community. Most accounts of coccinellid bites are little more than anecdotal speculation at best. But with the introduction of adventives species, these stories have greatly increased in frequency and seemed to warrant further investigation. Coccinellids of various species were collected in the wild, separated based on species, and subsequently reared in colonies in the lab. Trials were conducted by placing 40 coccinellids of a single species that were given either: 1) no food or water or, 2) aphids and water ad libitum, placed into a transparent enclosure with the experimenter’s hand and forearm. Coccinellids we’re marked with unique, distinguishing marks using Testor Paint and were allowed to roam freely. The movement, bite frequency and severity with which they bit into the skin was recorded using a comprehensive data system. Large adventives species such as Coccinella septempunctata were distinguished by a significantly higher propensity to bite and exhibited a startling blood feeding behavior that is not yet clearly understood. Native species such as Adalia bipunctata were in some trials, equally likely to bite as was Coccinella septempunctata but they did not exhibit the blood feeding behavior likely as a result of their inability to break through the skin. Coccinellids were consistently observed feeding in clusters. One bite seemed to trigger more in a localized area. Coccinellids without access to prey or water were significantly more likely to bite in most species implying that the purpose of biting is to acquire water or nutrients.