Lyttini

Associating with the Spanish fly
Published 12 December 2023

The classification of the blister beetles has been subject to numerous revisions over the years, with the status of many subgroups remaining uncertain. Perhaps the most uncertainty of all has surrounded the representatives of the tribe Lyttini.

Lydus trimaculatus, copyright Kostas Zontanos.

As a tribe of the subfamily Meloinae, the Lyttini have historically been united by features of the first instar larvae. Like most other blister beetles, lyttins begin their lives as parasites or kleptoparasites on other insects. They exhibit hypermetamorphy where the first larval instar (the triungulin) is distinct from later stages and adapted to seek out the nests of hosts. In some blister beetles, the triungulins are adapted for phoresy, hitching a ride on a larger insect to reach their host, but the newborn larvae of Lyttini lack such adaptations and must find their host by more active means. Lyttin triungulins are united by antennae with a long terminal seta, more than twice as long as the antenna itself. In most species, the abdomen lacks laterotergites and the spiracles are placed dorsally (Bologna & Pinto 2001). The hosts of Lyttini, where known, are usually bees though the southern African Australytta are associated with eumenine wasps (Bologna & Pinto 2002).

Triungulin larva of Teratolytta gentilis, from Riccieri et al. (2022).

In contrast to the fairly uniform larvae, however, adult Lyttini are structurally diverse and lack distinct unifying features. As such, it was not entirely surprising when a molecular phylogenetic analysis of the tribe by Riccieri et al. (2022) established found that the ‘lyttins’ were not monophyletic. Instead, Riccieri et al. found evidence of no less than eleven deeply divergent lineages interspersed alongside representatives of other tribes (and while they did not include any of the Neotropical ‘lyttins’, they noted that their distinctive appearance suggested that they too were not related to the core assemblage around the type genus Lytta). The implication is that the supposed ‘lyttin’ larva is potentially plesiomorphic for the Meloinae as a whole or a convergent adaptation to similar host relationships. Riccieri et al. (2022) suggested that the Lyttini should be restricted to a clade of five genera found in the Holarctic realm but did not describe what (if any) morphological features were characteristic of this clade.

Spanish fly Lytta vesicatoria, copyright Siga.

Whatever its circumscription, there is no question that the most notorious representative of the Lyttini is its type species Lytta vesicatoria, the beetle commonly referred to as the ‘Spanish fly’. This bright, metallic green beetle is widespread in the western Palaearctic, being particularly abundant in southern Europe. It is best known for the production of the defensive chemical cantharidin which, like other blister beetles, it exudes in a fluid from its mouth and joints as a defense against predators. This substance is highly toxic, causing blistering and bleeding from mucous tissues, and its ingestion has been implicated in more than one human death. Nevertheless, it also has a long history of being thought to have aphrodisiac properties, perhaps by people who took the expression ‘burning loins’ a little too literally. According to Wikipedia, It has even been used for culinary purposes, with crushed beetles an ingredient in certain variations of the Moroccan spice mix ras el hanout. Supposedly, however, the use of this component has been disallowed in recent decades, so while your ras el hanout may indeed be spicy, you can feel a bit more reassured that it is unlikely to be lethal.

References

Bologna, M. A., & J. D. Pinto. 2001. Phylogenetic studies of Meloidae (Coleoptera), with emphasis on the evolution of phoresy. Systematic Entomology 26: 33–72.

Bologna, M. A., & J. D. Pinto. 2002. The Old World genera of Meloidae (Coleoptera): a key and synopsis. Journal of Natural History 36 (17): 2013–2102.

Riccieri, A., E. Mancini, M. Pitzalis, D. Salvi & M. A. Bologna. 2022. Multigene phylogeny of blister beetles (Coleoptera, Meloidae) reveals extensive polyphyly of the tribe Lyttini and allows redefining its boundaries. Systematic Entomology 47: 569–580.

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