Snake scent gland secretions repel and induce contact toxicity in ants

Abstract

Embedded in the tail base of all snakes is a pair of scent glands from which typically foul-smelling secretions are expelled when snakes are disturbed. The tendency of predatory ants to avoid snake cloacal fluids, and the abundance and structural diversity of potentially insecticidal carboxylic acids identified in scent gland secretions (SGS), prompted speculation that SGS function to deter ants. We examined the deterrent properties of the SGS of the Middle American burrowing python (Loxocemus bicolor) in fumigation, repellency, and contact-toxicity behavioral assays against workers of the red imported fire ant (Solenopsis invicta) and a species of carpenter ant (Camponotus floridanus), thus representing the two major ant sub-families, Myrmicinae and Formicinae, respectively. We also examined responses by S. invicta to the SGS of representative booid, pythonid, colubrine, elapinine, and crotaline snakes. None of the SGS samples affected the two ant species in fumigation tests. However, in repellency bioassays, ants given a choice between a droplet of water or sugar water versus a diluted droplet of SGS overwhelmingly avoided the latter, typically exhibiting rapid antennation from within a few mm, then retreating. Pure or diluted SGS applied directly to ants induced a high percentage of paralysis and death. Some treated ants exhibited symptoms of contact toxicosis but recovered within a 4-h observational period. Our results and reports of the responses of predatory ants to the Texas blindsnake (Rena dulcis) point to the scent glands as an ancient and widespread source of ant deterrents.