PTILODACTYLIDAE Laporte, 1836
Toe-Winged Beetles
The single UK species, Ptilodactyla exotica occurs only in artificially heated greenhouses.
POLYPHAGA Emery, 1886
BYRRHOIDEA Latreille, 1804
Ptilodactyla Illiger, 1807
P. exotica Chapin, 1927
3.5-5mm
Suborder:
Superfamily:
Genus:
Species:
Size:
Introduction
As currently understood this family includes about 500 species in 34 genera and 5 subfamilies although many genera were formerly included in Dascillidae and Scirtidae and there are likely to be further changes, more than 360 species, or about 75% of the total, are included in the genus Ptilodactyla Illiger, 1807. The family is almost exclusively tropical and only very poorly represented in temperate regions; 26 species of 6 genera and 4 subfamilies occur in the United States and only 5 species of 2 genera and 2 subfamilies are Australian, none are endemic to Europe and only the single invasive species, Ptilodactyla exotica Chapin, 1927 has been recorded under artificial conditions. The Nearctic Araeopidiinae Lawrence, 1991 is monotypic. The Neotropical Aploglossinae Champion, 1897 includes about 12 species of the single genus Aploglossa Gúerin-Meneville, 1849. Anchytarsinae Champion, 1897 includes 7 genera among which Epilichas White, 1859 comprises 12 Oriental and Southeast Asian species, the Central American Anchytarsus Gúerin-Meneville, 1843 includes 5 species and the Madagascan endemic Daemon Laporte, 1836 includes about 35 species. Cladotominae Pic, 1914 includes 8 genera and more than 30 species and is pantropical; the monotypic Austrolichas Lawrence & Stribling, 1992 occurs in Queensland while the Madagascan endemic Hovachylia Fairmaire, 1901 includes 2 species. The remaining species, the vast majority, are included in the Ptilodactylinae Laporte & Castelnau, 1836 which includes 13 genera, and all but 32 species are included in Ptilodactyla. The monotypic Valoka Deléve, 1872 is endemic to Bismark Island (Papua New Guinea). Therius Gúerin-Meneville, 1849 includes 7 mostly African species, 2 of which are Madagascan endemics. Microdaemon Kolbe, 1897 includes 4 species from East Africa, and Pherocladus Fairmaire, 1881 includes about 10 species from Sumatra and Borneo. Ptilodactyla is pantropical with the greatest diversity in the Neotropics.
Ecology
Adults are terrestrial, mostly occurring in marginal wetland or permanently wet woodland situations; most have been recorded from waterside habitats, damp leaf-litter, decaying logs and, on occasion, beaver dams. They are most frequently taken at light, and usually in large numbers, but also occur by sweeping or beating vegetation in suitable situations or, in species where the larvae develop in leaf-mould, from Berlese extractions, and adults of all genera have been recorded from malaise traps. Adults of the Nearctic Araeopedius monachus LeConte, 1874 have been recorded in numbers from Sorbus flowers. All adults have the maxillae modified into ‘spore brushes’ and most are thought to feed upon moulds and micro fungi growing on leaves and decaying wood etc. The life histories of most are unknown but larvae of the Nearctic Paralichus trivittus (Germar, 1824) occur in shallow seeps on fine sandy substrates containing coarse fragments of organic detritus. Larvae are sometimes present in numbers from extraction samples taken from wetland margins and damp litter but so far as is known only those of the Central American genus Anchytarsus Guérin-Meneville, 1847 are properly aquatic, living in or on submerged wood. Those of the Nearctic Areapidius monachus (LeConte, 1874) (Araeopidiinae) live on stream margin substrates and though they possess gills apparently enter the water only by accident. In all known cases pupation occurs in the soil or among leaf-litter.
Description
Adult ptylodactylids vary widely in size, from 2-16mm, but most are below 6mm, they are elongate-oval, often almost parallel-sided, and usually rather drab pale to dark brown or, in part, black e.g. in Anchytarsus or many species of Ptilodactyla, only rarely bicoloured or patterned e.g. in Paralichus White, 1859. Dorsal surface glabrous to variously pubescent. Head hypognathous and partly inserted into the prothorax so mostly concealed from above, vertex usually simply convex, eyes lateral; round and convex, frontoclypeal suture distinct, clypeus and labrum transverse and often with a membrane visible in between. Antennae inserted laterally between the eyes and the mandibles, 11-segmented and filiform, serrate or pectinate, and often dimorphic; males often with an internal articulated process on segments 4 to 10, females usually filiform to serrate. Maxillae and labrum often modified with setose lobes and/or with dilated palps. Pronotum broadest at distinct posterior angles and curved and narrowed to a rounded anterior margin which at least partly covers the head, lateral margins with or without a border and the basal margin simple or, often, crenulate. Prosternum generally short in front of rounded and posteriorly open coxal cavities, the process narrow and often expanded towards the hind margin of the coxae, mesosternum short with a narrow intercoxal process, metasternum broad and often with a distinct median longitudinal impression. Abdomen with 5 visible and free ventrites, the fifth distinctly emarginate. Scutellum cordate to rounded and simple or notched across the basal margin. Elytra generally rather parallel-sided, completely covering the abdomen and continuously rounded apically, sometimes with prominent shoulders; smooth or with punctured striae but without raised carinae. Legs slender and often proportionally long, the pro- and mesocoxae conical, pro- and mosotrocanters small but obvious, and the metatrocanters large and sometimes lobed. Tarsi 5-segmented; the segments simple or lobed, in Ptilodactyla with the fourth segment small and hidden by the expanded lobe of the third. Claws simple or, in Paralichus, pectinate.
​
Many species are very similar in size and colour etc. and determinations should be based on male dissections; there is variation in the position and length of the lateral lobes but nonetheless all known species may thus be identified. Females can only be assigned by association.
Fully grown larvae vary from 3-15mm; they are elongate, cylindrical and usually curved ventrally, in Ptilodactylinae the abdominal apex is strongly curved down, creamy to dark brown in colour and with scattered conspicuous setae across the dorsal surface. The prothorax is longer than the meso- and metathorax and the abdomen 10-segmentedl the ninth tergite is concave or convex , and with or without small urogomphi, the ninth sternite is unmodified and the tenth segment generally with small ‘hooks’ on a pair of lobes. In some, thought to be aquatic, with several gills in an anal membrane. Mesothorax and abdominal segments 1-8 with distinct spiracles. The head is prognathous and prominent, not retracted into the prothorax, with relatively long 3-segmented antennae, 4-segmented maxillary palps and tridentate mandibles bearing articulated processes, setae or brushes of pubescence.
Ptilodactyla exotica Chapin, 1927
This tropical species, probably native to Mauritius and recently found on Réunion Island, has become acclimatized and established in heated premises in many areas across Europe including Scandinavia and the U.K. It was almost certainly introduced with imported exotic plants and continues to develop on these in artificially heated environments. Most European records are from the last few decades and it has also recently been discovered in the north-western United States. In the U.K. it has become established in heated greenhouses at Kew Gardens and Cambridge. Larvae develop in moist and heated soil, feeding on microfungi and spores, and adults become active in the evening, running and taking short flights when disturbed.
​
A small elongate species; males 3.5-4.0mm and females about 5.0mm, dark brown with the head and antennae darker. Entire dorsal surface punctured, the pronotum more strongly so than the elytra. Eyes convex and proportionally large, more so in the female. Female antennae weakly serrate, male antennomeres 4-10 with a long internal process. Pronotum and elytra weakly and separately rounded. Pronotum rounded laterally and produced over the base of the head, broadest in front of the base, posterior angles slightly acute, basal margin very finely crenulate and curved medially around the base of the heart-shaped scutellum. Elytra randomly punctured; towards the suture and apex with impressed and punctured striae, lateral margins explanate and continuously rounded apically. All tibiae densely pubescent. Third tarsomere strongly but narrowly lobed.
Further Reading