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On this page I will discuss in turn:
One night in early September of 1995 I was walking on my field site when I noticed that something unusual was going on at one of the Aphaenogaster cockerelli nests there. Instead of just a few workers hanging around the nest entrance, there were large numbers and many were carrying larvae, pupae, and even immature reproductives.
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While the night was certainly a very pleasant one, it somehow seemed unlikely that the adult ants had brought their offspring out to enjoy it. Anyway, I took some pictures and was ready to leave when suddenly ants began scattering from the nest entrance. Almost simultaneously a western blind snake (Leptotyphlops humilis) popped out of the nest and wriggled off into the night.
This was actually the third time that I had seen a blind snake associated with ants on or near my plot. The first time was in the late summer of 1993. On that occasion I had come out to a place where the night before I had watched a Neivamyrmex colony go into bivouac near a large creosote bush.
The second time I saw a blind snake was much less eventful. On a late summer evening after a rainstorm one came up out of Crematogaster opuntiae nest. I kept the snake for a few weeks, photographed it, and then released it.
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Western Blind Snake. To |
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It is not by coincidence that all these snakes were seen going into and out of ant nests. In addition to termites, snakes in this genus frequently prey on ant eggs and larvae (Reid 1963; Watkins et al., 1967; Baldridge and Wivagg 1992).
Unfortunately, I was unable to find anything in the literature about the natural history of L. humilis. It is perhaps informative, though, to consider some of the behaviors that have been documented for a related species,L. dulcis (the Texas blind snake). Watkins et al. (1967) observed that these snakes actively seek Neivamyrmex colonies by following their trails. They hypothesized that L. dulcis finds Neivamyrmex colonies by following the pheromone trails these ants lay down. To explore this they compared these snakes' behavior on Neivamyrmex and distilled water trails. Not only were the snakes much more likely to follow the Neivamyrmex trails, they also behaved differently. Snakes in the Neivamyrmex treatment frequently reared their heads (apparently an olfactory orientation behavior) while they never did this in the distilled water treatment. The snakes also did this when termites or ant brood were put into their containers.
Another interesting aspect of the predatory behavior of L. dulcis is how it avoids being attacked by ants. Going into an ant nest nest can be a dangerous thing; ants are often fierce in defense of their homes. Many bite invaders and some even sting them. Apparently, there may be two separate ways in which L. dulcis protects itself (Gehlbach et al. 1968). First, if a snake is attacked by ants it immediately discharges feces and a clear, viscous liquid that ants find quite repulsive. The snake then writhes in this secretion while simultaneously tilting the individual scales on its body in a direction perpendicular to its body axis (apparently this often results in a slight color in the animal). This last action creates little pockets all over the snake's body that presumably catch and retain the repulsive secretion. After a snake is thoroughly covered by this secretion ants refuse to attack it for for 3-30 minutes.
The second way in which blind snakes protect themselves is less understood but possibly more ingenious. Gehlbach et al. (1968) noted that L. dulcis individuals often move down army ant trails without the ants taking any apparent notice. They also observed that a snake is only attacked once if kept in a laboratory ant colony. From these two observations, Gehlbach et al. (1968) argue that blind snakes may also occasionally acquire certain ant odors which curtail further attacks. Such a strategy would be most effective if individual snakes typically prey on a particular ant colony for an extended period of time.
While a little is known about how blind snakes hunt ants, there is very little information on how ants resist their attacks. The observation that A. cockerelli workers will remove larvae from their nest when it is invaded may be the first example of an effective response by ants to blind snake predation. I should also point out that in November of 1994 I observed an Ephebomyrmex pima colony where the workers also brought their larvae and pupae to the surface. Whether these ants were responding to an invading blind snake is not known, and whether bringing offspring to the surface is a general response to blind snake predation remains to be seen.
Baldridge, R.S. and D.E. Wivagg. 1992. Predation on imported fire ants by blind snakes. The Texas Journal of Science 44: 250-252.
Gehlbach, F.R., J.F. Watkins II, and H.W. Reno. 1968. Blind snake defensive behavior elicited by ant attacks. Bioscience 18: 784-785.
Reid, J.R. and T.E. Lott. 1963. Feeding of Leptotyphlops dulcis dulcis (Baird and Girard). Herpetologica 19: 141-142.
Watkins, J.F. II, F.R. Gehlbach, and R.S. Baldridge. Ability of the blind snake, Leptothyphlops dulcis, to follow pheromone trails of army ants, Neivamyrmex nigrescens and N. opacithorax. The Southwestern Naturalist 12: 455-462.
Copyright (c) 1998 Barry Sullender
Rice University
All rights reserved