Calling nestmates to the rescue

A blog post highlighting the article by K. Miler & K. Kuszewska in Insectes Sociaux

Written by  Krzysztof Miler

Pit-building antlion larvae are predatory neuropterans which co-occur with some sand-dwelling ants, their main prey. The ants evolved rescue behaviours as means of avoiding antlion predation: when an ant stumbles into the pit and is captured by an antlion larva, its nearby nestmates may act to free it. No one knows how exactly that happens.

ant lions

An example of the “antlion zone” with several antlion larvae pits (conical traps). When an ant stumbles inside one of these pits, its near-by nestmates may come to rescue. Photo: K. Miler [Błędowska Desert, Poland].

In 2002, Czechowski and his co-authors [1] observed that some species of ants rescue their nestmates from the pits of antlion larvae. Since their discovery, several papers about this phenomenon have been published. However, no one knows how exactly rescue behaviour is elicited. The main hypothesis states that when an ant stumbles into the pit of the larva and gets captured, it sends some kind of signal (“call for help”) which summons its nearby nestmates to the site of capture and triggers their rescue behaviour, but the form of this signal remains unknown.

I recently published a paper saying that soon-to-die ants stop calling for help and thus elicit lower levels of rescue than longer-lived individuals [2]. Prof. Martin Collinson tweeted shortly after my publication: “Moribund ants do not call for help. They’re probably too knackered to use their little ant smartphones.” But the call for help likely doesn’t come from a tiny smartphone.

If rescue is indeed elicited by a call for assistance, then in my study species, Formica cinerea ants, the “call for help” signal is most likely chemical, originating from one of glands releasing volatile substances. Together with my colleague, Karolina Kuszewska, we performed two experiments to test whether mandibular gland excretions elicit rescue behaviour. We focused on mandibular glands because they were obvious candidates due to their other communication functions in ants.

In the first experiment, we impaired communication of some ants via their mandibular glands and checked whether they were rescued less frequently than other ants with unchanged mandibular communication skills. In the second experiment, we dissected some ants and checked whether the content of their mandibular glands applied onto dummy-ants made of pieces of toothpicks would elicit rescue from nearby (real ant) nestmates.

Apparently, mandibular glands have nothing to do with the elicitation of rescue behaviour in F. cinerea. Blocking the release of excretions of mandibular glands has no effect on rescue frequency, and applying the content of these glands onto dummies elicited no rescue towards them. Our study is the first one to look into the mechanism of the “call for help” signal. We plan to perform another set of experiments looking into gaster-tip glands, aiming at finding out whether the mechanism of rescue behaviour in ants is as we currently assume it is. We expect that we won’t find a tiny Bluetooth device either.

An ant captured by an antlion larva summons its nestmate to the site. The rescuing ant grabs the victim by its leg and pulls, holding on even when the antlion larva starts to bury deeper in the sand to prevent losing its victim as a result of this rescue action. Unfortunately for the victim, the rescuing ant is not successful. Video: K. Miler [Jagiellonian University, Poland].



[1] Czechowski et al. 2002, Ann Zool 52:423-431.

[2] Miler 2016, PLoS ONE 11:e0151925.

Find out more in Hollis et al. 2015.

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