Extant pygmy grasshoppers (Tetrigidae) that possess wings have the forewings reduced into scale-like tegmenula, while hind wings remain fully developed. Rusmithia gorochovi gen. et sp. nov. (Tetrigidae, Batrachideinae, Rusmithini trib. nov.) is described based on a single adult female holotype from Lithuanian Baltic amber, from the Bartonian-Priabonian age, some 40 million years ago, and this is the only known tetrigid in which tegmenula or tegmina (the forewings) extend as far as half the length of the hind femur. Besides this very unique trait, other characters of Rusmithia gen. nov. indicate similarity with extant and especially fossil Batrachideinae (genus Danatettix Thomas, Skejo & Heads, 2019). Because of the strong differences this genus and Danatettix have with American Batrachideinae, they are assigned to a new tribe, European Batrachideinae or Rusmithini trib. nov. Acrydium bachofeni (Zeuner, 1937) might belong to this or a sibling genus based on its very long tegmenula or Succinotettix chopardi Piton, 1938, based on its 19-segmented antennae; neither species is tranferred as their types could not be examined.

Amber, autapomorphy, Baltic, European Batrachideinae, fossil, plesiomorphy, tegmina, Tetrigidae

Although many have dedicated their lives to studying them, our knowledge of extant pygmy grasshoppers (Orthoptera, Tetrigidae) is still scarce (Cigliano et al. 2023). Given this, it is unsurprising that the available information on extinct species of the family can easily be summarized in a single table (Table 1). Such a small dataset paints a tragically incomplete picture of their evolution—a picture that is slowly being painted one fossil at a time (Sharov 1968, Thomas et al. 2019).

Most of the extant tetrigid species have fore- and hind wings. The forewings of these species are reduced to tiny scales and are called tegmenula in pygmy grasshoppers, as opposed to tegmina in winged crickets and grasshoppers. The hind wings of pygmy grasshoppers are functional and are referred to as alae, as in other orthopteran families (Harz 1969, Devriese 1991, 1999). The longest tegmenula have been found in †Prototetrix Sharov, 1968 and †Archaeotetrix Sharov, 1968 (Sharov 1968), although it is not clear whether they represent stem Tetrigidae or specialized Locustopsidae (Heads et al. 2014, Thomas et al. 2019). It is also not clear how long the wings were relative to body size, as the wings are the only well-preserved part of species in these genera (Sharov 1968). Because of †Prototetrix and †Archaeotetrix, it is believed that the evolution of pygmy grasshoppers included a reduction in the size of forewings (Sharov 1968).

Herein, we describe a new genus and species, †Rusmithia gorochovi gen. et sp. nov. (Batrachideinae: †Rusmithini trib. nov.), an extinct tetrigid from Lithuania found in Baltic amber. With tegmenula reaching the mid-portion of the hind femora, this species is the new record holder for the longest tegmenula, which makes it an invaluable snapshot of the evolutionary history of Tetrigidae.

The holotype of Rusmithia gorochovi gen. et sp. nov. was purchased on eBay by Ru Smith who then contacted the first author. The female holotype is deposited in Ru Smith’s private collection, York, UK.

The widest possible age range of Baltic amber is 25 to 43 million years (Sadowski et al. 2017), but it is currently unclear whether the younger deposits are simply redeposits of the older material, so the usual age estimate is Lutetian (47.8–41.2 Ma) to Priabonian (37.8–33.9 Ma) (Seyfullah et al. 2018), with most of the material dated to the Priabonian (Sadowski et al. 2020). We refer to our fossil as belonging to the Middle Eocene following the Lutetian–Priabonian estimates. The holotype was photographed and drawn by Ru Smith. Characters relevant for subfamily classification are number of antennal segments (>19 in Batrachideinae, <18 in other subfamilies), shape of paranota (rectangular in Batrachideinae, triangular in other subfamilies), and morphology of the legs (with sulcate dorsal margin in Batrachideinae, carinated in other subfamilies). As a result, the new genus is assigned to Batrachideinae. Taxonomy follows that of the Orthoptera species file (Cigliano et al. 2023). Morphological terminology follows Tumbrinck (2014), and nomenclature is in accordance with the International Code of the Zoological Nomenclature (ICZN 1999).

The long tegmenula of Rusmithia gorochovi are peculiar in that the radius and costa are clearly visible, unlike in any other known tetrigid. A similar pattern of venation can be observed in Tridactyloidea (Sharov 1968), which modern analyses have reconstructed as basal Caelifera (Song et al. 2020). This seems to imply that this morphology may be ancestral in Tetrigoidea, but such a conclusion cannot be drawn at the moment for several reasons. First, it has been shown in different taxa that reduction in wing size is a relatively common occurrence and is followed by a reduction in wing venation, with only the veins crucial for wing armature persisting (Perfilieva 2010, Žikić et al. 2017). This means that it is impossible to exclude convergence based only on the present data. Second, Danatettix hoffeinsorum, a European relative of Rusmithia gorochovi, and Eotetrix unicornis, an American fossil Batrachideinae, both have typical tetrigid tegmenula (Gorochov and Labandeira 2012, Thomas et al. 2019), which casts doubt on the continuous persistence of this morphology through time. Acrydium (?) bachofeni is stated as having long tegmenula by Zeuner (1937), meaning that it could belong to Rusmithia or a new closely related genus. Examining the type of this species would help elucidate the taxonomy of European Batrachideinae and the evolution of tegmina in this group. Third, Archaeotetrix and Prototetrix, which are much older than Rusmithia, also exhibit long tegmenula but with different venation (Sharov 1968), although their affinities remain obscure. The most parsimonious explanation is that Rusmithia belongs to a line of Batrachideinae in which the longer tegmenula were retained, which may represent an intermediary state between the fully winged ancestral form and the more modern, reduced forms. This implies the possibility that tegminal reduction occurred at least twice in Tetrigoidea. More research is needed to clarify the evolution of Tetrigoidea and their wings.

Baltic amber is a gold mine for fossil arthropods (Weitschat and Wichard 2010), comparable to the number of plant taxa described from the same deposits (Sadowski et al. 2020). A recent botanical study by Sadowski et al. (2020) revealed the presence of various habitats in the Baltic region, ranging from coastal swamps to mixed mesophytic conifer-angiosperm forests with a wide range of transitionary habitats between them. Similar habitats are found today in the warm-temperate regions of East Asia and North America, and they house numerous species of modern Tetrigidae, including Batrachideinae (Cigliano et al. 2023). Thus, with relative certainty, we can conclude that Rusmithia gorochovi likely spent its time in warm and wet habitats feeding on algae, mosses, and detritrus in unknown proportions (Hochkirch et al. 2000, Kuřavová et al. 2020). The fly trapped together with the holotype of R. gorochovi (Fig. 3) belongs to the family Sciaridae (det. Andrew Ross), which feed on detritus and fungi (Gerhardt and Hribar 2019), indicating their shared habitat.

Fig. 3. 

A fly belonging to the family Sciaridae, encapsulated together with Rusmithia gorochovi gen. et sp. nov.

The fossil record of Tetrigidae is scant, and much more work needs to be done. Most notably, the placement of Archaeotetrix locustopseiformis and Prototetrix reductus within the taxonomy of Tetrigoidea is unclear (Sharov 1968, Thomas et al. 2019), if they indeed belong to this superfamily. Because the venation of the tegmina of these species differs from both the extant and other known extinct tetrigids, it should be closely examined as it could indicate that these two species are only distantly related to the other known tetrigids. Furthermore, the types of Acrydium (?) bachofeni, Succinotettix chopardi, and Heer’s (1856) Tettigidea (?) gracilis could not be examined, and their affinities remain unclear. If and when they are found, they will undoubtedly shed much-needed light on the evolutionary history of Tetrigidae.

We are infinitely grateful to Ru Smith who purchased the specimen and made it available for scientific description, took many photographs of the holotype, and made the drawing included herein. We thank the Orthopterists’ Society for their support in publishing this article.