Mites (Acari) as supposed prey of long-legged flies (Diptera: Dolichopodidae) from Eocene Baltic amber

Abstract

Nearly all extant dolichopodids are known (Ulrich, 2004) or suspected to be predators in their imaginal stage and are most probably also as larvae. A striking exception is found in two genera in the Medeterinae Lioy, 1864 viz. Thrypticus Gerstäcker, 1864 and—according to the morphology of the female ovipositor, also Corindia Bickel, 1986. Larvae of Thrypticus are phytophagous (Kechval & Pollet, 2024) and no observations on prey consumption by the flies are available. This might relate to a reduction of mouthparts of these dipterans. In his 2004 work, Ulrich listed 13 literature citations in which Arachnida were reported as prey of long-legged flies. Eleven of these definitively refer to mites; as prey mainly of species of Medetera Fischer von Waldheim, 1819. Medeterinae are rather common in Eocene amber and eight genera with fossil species preserved in amber are known (Grichanov, 2025a, b) whereas one genus, Atlatlia Bickel, 1986, is known to have extant diversity concentrated in the Australian realm and the Polynesian subregion of the Palaeotropic realm (New Caledonia) (Bickel & Martin, 2025). Medetera itself is only known from extant species and is the most species rich genus in this subfamily with 424 species worldwide (Yang et al., 2006; Schrameyer & Stark, 2026) and many more await description. One of the most common members of Dolichopodidae in Baltic amber is the genus Palaeomedeterus Meunier, 1895 in the subfamily Peloropeodinae Robinson, 1970 (Stark, unpubl. pers. observ. by checking thousands of Diptera inclusions over the last 30 years). As to the subfamily-classification of the Dolichopodidae it can only be reiterated that the search for evolutionary lineages, which might be interpreted as subfamilies, is an ongoing process. Several evolutionary-biological phenomena—such as heterobathmy and homoplasies—influence the result. Paying attention to the structure of the mouthparts is important for this classification. However, their form and function are, in themselves, subject to the same premises. Grichanov & Negrobov (2018) adopted Robinson’s (1970) subfamilies of Dolichopodidae regarding the contemporary classification of fossil genera. His interpretation of the subfamily should be given here in brief (slightly modified from that published by Grichanov & Negrobov, 2018): arista-like stylus apical to dorsal, postpedicellus often only as long as broad, but sometimes enlarged, triangular, or with two more or less pointed tips; scapus bare, acrostichals uni- to biseriate, scutum with a flattened asetose area apical to the scutellum; R₄₊₅ unforked, parallel to subparallel to M₁; mid and/or hind femora with preapicals; hypopygium large or small, often globose in the resting position, loosely folded forward beneath the abdomen (ventroflexion), female tergite 10 with strong acanthophorites.