Snakes produce kairomones that induce aggregation of unfed larval blacklegged ticks Ixodes scapularis (Acari: Ixodidae)

Abstract

We have observed in the field copperhead snakes with Ixodes scapularis larvae feeding near the head and cloaca opening. Results show that copperhead excreta acts as a host cue that causes a significant proportion of unfed I. scapularis larvae to stop crawling, curl their legs, and remain motionless in short range bioassays. Clustering of larvae on snake excreta-treated surfaces occurred within one hour and aggregations remained for up to 12 hours. Shed skins of copperheads also prompted arrestment of larval activity (i.e., mobility has stopped). Similar levels of arrestment were noted when testing shed skins and excreta from captive ball pythons (Python regius), Burmese pythons (Python moralus), Mexican cantils (Agkistrodon bilineatus), and variable kingsnakes (Lampropeltis mexicana), suggesting that chemical cues utilized by larvae are similar among snake species. Larvae reacted positively by arresting to uric acid (main purine component in reptile excreta) and squalene (main lipid on shed snake skin). Uric acid and squalene function as tick arrestants, not attractants; physical contact with these compounds is required in order for larvae to settle. Snakes defecate and molt outside dens. The conclusion is that snakes generate two tick kairomones, uric acid and squalene. These compounds promote off-host clustering of unfed I. scapularis larvae in areas likely to be frequented by snakes and their prey such as mice, small lizards, and ground-dwelling birds that serve as tick hosts.