The butterflies of the Phengaris genus (also known as Maculinea) are known to be brood parasitic. During the fourth instar, the caterpillars leave their food plant and mimic ant larvae, causing the ants to take them back to their nest as if they were ant larvae that had escaped.
While in the nest, the caterpillars mimic ant larvae by means both of surface chemicals and acoustic mimickry (including, I understand it, mimicking sounds made by queens!) After pupating, the pupa continues to engage in acoustic mimickry, although I can't find any reference to whether it does (or even could!) engage in continued chemical mimickry.
But I can't find anything in the literature regarding the adult butterfly's emergence from the pupa and exit from the ant nest. A non-academic book and some web pages claim that the alcon blue (Phengaris alcon) and mountain alcon blue (Phengaris rebeli) adults are no longer engaged in any form of mimickry at this point, and may be attacked by the ants. These accounts differ as to how likely an attack is, how much danger the butterfly is in, and the level of protection afforded by the butterfly scales.
The webpages I mention belong to a University of Copenhagen researcher (Dr. David Nash) who has published work in this field. This suggests that the claim is probably correct.
That said, none of the peer-reviewed publications coauthored by him appear to mention it, and each of the two webpages creates a different impression as to the level of danger involved:
"If an ant tries to bite the butterfly it will only get a mouthful of scales." states one, suggesting that there is little the ants can do to harm or hinder the butterfly. But the other states "The adult has to get out of the ant nest quickly to prevent the ants killing it."
The book is written by someone else. It cites three papers, which do discuss the larvae/pupae and ants. But none of these have any information regarding this specific topic.
A paper by Elfferich provides some information in the case of Phengaris nausithous, the so-called "dusky large blue". The author states: "The butterflies always emerged between 00.00 and 06.00 and walked out of the nest ... During the night there was only a little ant activity and there was no real aggressive behaviour ... we may conclude that no pheromone to reduce aggression of the ants is produced by the butterfly."
Some published books (not from the academic literature) claim that the "large blue" (Phengaris arion) continues acoustical, and (according to one book) chemical mimickry. Far from being in danger, two of the books claim that they are escorted outside by ants as though they were acting as a bodyguard!
I believe that this is probably true. The reason for this is that two of the books (pub. 2008 and 2010 were describing discussions between the authors and Jeremy Thomas, an Oxford professor who has published research in this field. In fact, Professor Thomas's research identified the butterfly's dependence on ants, the reasons for its decline in the UK, and he was able to reintroduce the species after it became extinct in the UK. The other book (pub. 2014) mentioned Professor Thomas repeatedly, and described a book by him as "One of the essential wildlife books".
Even so, I don't have access to material in which Professor Thomas or any of his colleagues actually state this instead of just being mentioned by others. So it's still second hand information covering only one Phengaris species.
And to complicate matters further, in a paper that predates the three books, Thomas and other researchers stated that Phengaris arion and Phengaris teleius (scarce large blue) adults "show no interaction with ants after eclosion from pupae in the outer cells of Myrmica nests, from which they emerge while the ants are quiescent in the early morning".
Does anyone know of any peer-reviewed sources which confirm, for the various species, whether:
- The adult butterfly continues to engage in mimickry?
- Whether this is chemical, acoustic, or both?
- The ants are more likely now to realise it's an intruder, and may attack it?
- How likely this is?
- How much danger are the butterflies in, if so?
- Some accounts claim that the alcon/rebeli has scales which make it impossible for attacking ants to grasp them. Others refer to the scales protecting them from being bitten. If these attacks are a risk, how well is the butterfly protected and do attacks from angry ants still get through?
I've looked at too many papers to list here, but my sources include:
Barbero F, Thomas JA, Bonelli S, Balletto E and Schönrogge K. (2009). Queen Ants Make Distinctive Sounds That Are Mimicked by a Butterfly Social Parasite. Science 06 Feb 2009: Vol. 323, Issue 5915, pp. 782-785. DOI: 10.1126/science.1163583
Thomas JA, Schönrogge K and Elmes GW. (2005). Specialization and host associations of social parasites of ants. In: Insect Evolutionary Ecology: Proceedings of the Royal Entomological Society's 22nd Symposium (Fellowes M.D.E., Holloway G.J. and Rolff J., Eds). 475–514
Als TD, Nash DR, and Boomsma JJ. (2001). Adoption of parasitic Maculinea alcon caterpillars (Lepidoptera : Lycaenidae) by three Myrmica ant species. Animal Behaviour, 62, 99-106. https://doi.org/10.1006/anbe.2001.1716
Akino T, Knapp JJ, Thomas JA and Elmes GW. (1999). Chemical mimicry and host specificity in the butterfly Maculinea rebeli, a social parasite of Myrmica ant colonies. 266 Proc. R. Soc. Lond. B. http://doi.org/10.1098/rspb.1999.0796
Elfferich NW. (1998). New facts on the life history of the dusky large blue Maculinea nausithous (Lepidoptera: Lycaenidae) obtained by breeding with Myrmica ants in plaster nests. DEINSEA 4: 97-102. ISSN 0923-9308
Elmes GW, Thomas JA and Wardlaw JC. (1991). Larvae of Maculinea rebeli, a large‐blue butterfly and their Myrmica host ants: patterns of caterpillar growth and survival. Journal of Zoology, 224: 79-92. doi:10.1111/j.1469-7998.1991.tb04789.x
Elmes GW, Thomas JA and Wardlaw JC. (1991). Larvae of Maculinea rebeli, a large-blue butterfly, and their Myrmica host ants: wild adoption and behaviour in ant-nests. Journal of Zoology, 223: 447-460. doi:10.1111/j.1469-7998.1991.tb04775.x