When we think about ticks, we mostly concentrate on their ability to vector disease. This is especially true of Ixodes scapularius, or the black legged tick or the deer tick, which is responsible for transmitting up to sixteen different diseases. Ixodes scapularis is most notorious for its ability to spread Borrelia burgdoferi, which is the bacterium that causes Lyme Disease. However, what we often don’t consider is the way that ticks interact with their fellow arthropods. Ticks, particularly the nymphs, are common prey of other arthropod predators such as spiders and ants. This type of biological control could be the key to unlocking new means of tick management, as previous studies have documented that the presence of ants can negatively affect tick abundance. However, it was not clear on how ticks could identify that ants were present in an area.  

 

So how do ticks “crack the code” when it comes to avoiding potential predators? This study sought to understand some of the mechanisms concerning predator avoidance behavior in ticks, specifically looking at how Ixodes scapularis responded to the semiochemicals, or the communication signals that Formica oreas, or thatching ants, produced.

To test tick avoidance of ant semiochemicals, the ticks were offered a choice test between two chambers that were lined with filter paper. One chamber featured 20 ants that were permitted to walk around the chamber for 16 hours, while the other was the control chamber that only featured filter paper without any arthropod exposure. The ticks were allowed 20 hours to “respond” to the choice test being offered to them, and their final location was noted. Most ticks who responded to the choice test exhibited avoidance behavior of filter paper that had been previously touched by Formica oreas workers. 

 

The researchers then looked at which chemicals may be causing the avoidance behavior by dissecting the poison gland and the Dufor’s gland of the Formica oreas workers. Both glands are found in the abdomen of the ant and are important for secretion of semiochemicals, meaning that they’re essential organs for ant communication. As previous studies had shown, the semiochemicals produced from the poison gland and the Dufor’s gland were different, with the poison gland producing formic acid and the Dufor’s gland producing hydrocarbons. Ticks were offered choice tests of semiochemicals isolated from the poison gland alone, the Dufor’s gland alone, and both glands combined. Ticks did not exhibit any avoidance behaviors with the semiochemicals derived from the poison gland alone, or the Dufor’s gland alone, but did show avoidance behavior to the chemicals when they were combined. The researchers duplicated this experiment using synthetic compounds derived from the poison gland (which was formic acid), and the Dufor’s gland (which was hydrocarbons). Once again, the formic acid and the hydrocarbons by themselves did not elicit a response from the ticks, but the formic acid and the hydrocarbons combined lead to the ticks avoiding that filter paper.  

 

Lastly, the researchers also examined what kind of response the ants would have to these derived semiochemicals. Ants were presented with two options: a piece of filter paper that had been soaked in the synthesized semiochemicals, or a piece of filter paper that had been soaked in dichloromethane as a control. In the choice test with Formica oreas workers, the workers were more likely to interact with the filter paper with the synthesized semiochemicals, which showed that the ants responded to the synthesized semiochemicals in the same way that they would respond to the naturally produced semiochemicals. In particular, these synthesized chemicals elicited an alarm-recruitment response, which called more ants to the area with the filter paper with the synthesized semiochemicals. Makes sense that ticks want to avoid an area with more ants potentially coming to it! 

This study documented that ticks have a clear avoidance response to ant semiochemicals. By paying attention to and spying on ant semiochemicals like formic acid and ant hydrocarbons, the ticks can potentially avoid predation by ants, and like James Bond, live to Die Another Day. Additionally, formic acid and hydrocarbons are extremely common communication signals to many ant species, which suggests that Ixodes scapularis may be spying on not just this species of ant, but many different species. Interestingly, these two species rarely interact with each other, as Formica oreas is generally restricted to the northwestern parts of North America, while Ixodes scapularis is mostly restricted to the eastern part of North America. However, given the adverse reaction the ticks had to this particular species, it suggests that tick avoidance is likely tuned to many ant species. 

This study presents potential for a new generation of tick repellents, that could easily be synthesized from ant semiochemicals. Low concentrations of formic acid are approved for use in cosmetics, meaning that we could see clothing-based and topical tick repellents made from synthesized ant semiochemcials eventually down the line. Overall, what I think this study proves is that we need to dedicate a little more attention to the antics of ants and ticks to determine new repellent strategies for tick management. 

Article by Laura Rosenwald, BCE

References: 

Burtis, J.C., Pflueger, C.  2017. Interactions between soil-dwelling arthropod predators and Ixodes scapularis under laboratory and field conditions. Ecosphere, Vol. 8, Issue 8. E01914. https://doi.org/10.1002/ecs2.1914 

Zingg, S., Dolle, P., Voordouw, M.J. et al. 2018. The negative effect of wood ant presence on tick abundance. Parasites Vectors 11, 164. https://doi.org/10.1186/s13071-018-2712-0 

Gooding Claire E., Pinard Charlotte, Gries Regine, Devireddy Anand and Gries Gerhard 2024 Blacklegged ticks, Ixodes scapularis, reduce predation risk by eavesdropping on communication signals of Formica oreas thatching antsR. Soc. Open Sci.11231355231355

Podcast