Grypus equiseti (Fabricius, 1775)
This is a widespread and native species across the Palaearctic, Asian and Nearctic regions, occurring to high latitudes in Alaska, Canada and Scandinavia etc. It occurs through Europe from France eastwards including the Mediterranean countries and the U.K. It has also become established elsewhere e.g. New Zealand after being introduced as a biological control agent. In the U.K. it is widespread though local throughout England and Scotland with records scattered to the far north although it seems to be absent from the West Country and in Wales it is mostly coastal. Host plants include two species of Equisteum; E. arvense (Field horsetail) and E. palustre (Marsh horsetail), both of which are common in wetland situations and on damp grassland in the U.K. On the continent they have been observed feeding on other Equisetum species. The adults are rarely seen, they are nocturnal and resemble the growing tips of the host plants but will occasionally be found by sweeping and will turn up in pitfall traps set among the host; they feed nocturnally on the stems but will fall to the ground and remain still for some time when disturbed. They have a long season, from February to November, and are thought to disperse by flight during May; they have not been recorded in flight but the elytra are not fused and the wings are well developed. Mating occurs from May to August. The females use their sharp and pointed mandibles to bore holes into the stems into which they insert one or, rarely, several eggs, most stems will host a single egg but occasionally several oviposition sites will occur between the nodes on a single stem. The larvae feed initially within the stems, moving down as they do so, but the final stages will feed within the rhizomes where they will also pass the winter before entering the soil to pupate.
4-6.8mm. A characteristically marked and convex weevil which should not be mistaken for any other U.K. species. The head is dark and marked with dense pale scales inside the convex and prominent eyes, the rostrum long with ventrolateral scrobes which are not visible from above and the antennae inserted about a quarter of the rostral length from the apex. Pronotum quadrate with rounded lateral margins which are broadest about the middle,
Grypus equiseti 1
Grypus equiseti 2
the surface strongly and closely punctured and clothed laterally with pale round scales. Elytra broadest behind the middle and sinuate apically, with prominent shoulders and interstices 3, 5 and 7 raised towards the apex. The striae are well impressed and punctured. The lateral margins, apex and a small patch on the apical third of interstice 3 with pale round scales. Legs pubescent; dark with the tibiae often paler and the femora not toothed. The pro-tibiae are straight along the outer edge, sharply angled at the apex, the apical margin rounded and the inner apical angle strongly produced. Tarsi with the basal segments variously dilated and the third segment strongly bilobed, the terminal segment elongate. Claws short, smooth and separate to the base.
GRYPUS Germar, 1817
A Holarctic genus of 6 species of small and very characteristic weevils, all of which feed upon and develop within horsetails (Equisetum spp). Two species, G. brunnirostris (Fabricius, 1792) and G. equiseti (Fabricius, 1775), have an almost Holarctic distribution. G. leechi Cawthra is Nearctic while G. rugicollis Voss occurs in China, G. kaschmirensis Voss in India, and G. mannerheimi Faust is more widespread across Siberia and Japan.