Mononychus punctumalbum (Herbst, 1784)
With the exception of Scandinavia this species occurs throughout Europe and extends eastwards into Siberia; it is the only member of the genus to occur in the U.K. where it is locally abundant on the Isle of Wight and along coastal regions of South Dorset, South Devon and North Somerset. In the U.K. the hosts are Iris foetidissima and I. pseudocarus while on the continent other species are also chosen e.g. I. germanica and I. barbatus. Typical habitats are damp areas around woods and scrub margins, dune slacks and cliffs and, at least in North Somerset, they have occurred in domestic gardens. Adults appear in May or June and feed on the host foliage; at this time they may be seen swarming and mating on the leaves, sometimes in large numbers. Oviposition occurs in June and July; the female bores into developing seed pods and inserts an egg into several of the seeds so that by late in the season most of the contents have been consumed, these holes are quickly repaired as the plant exudes a sticky liquid which seals them and so the larvae are safe to develop within. Development is rapid and they are fully grown by August or September and pulling the pods apart at this time may reveal the white fleshy pupae within. New generation adults appear in late August and September when they will feed briefly before entering the leaf litter to overwinter.
The large size, 3.9-5.1mm, and dark colouration will identify this species, more especially so as it is the only U.K. species to feed on Iris. Entirely black but for a white scutellary macula, pale antennae and some large pale scales to the underside and the femora. Dorsal surface with dense small and dark scales, those on the base of the rostrum and the temples broad and pale brown. Head with dense and moderately large punctures, smooth but for a deep impression on the frons. Antennae relatively short; the funiculus 7-segmented and the club tiny. Pronotum transverse and rounded laterally, densely and strongly punctured and with a broad median longitudinal impression. Scutellum usually with a few broad pale scales. Elytra broadly oval with prominent shoulders, the striae punctured and deeply impressed, the interstices broad and densely punctured. All tibiae with a small subapical tooth. In the male the meso- and metatibiae have obvious apical spurs and the pygidium is raised medially. Females lack the apical spurs and have a smooth pygidium. Each tarsus has a single claw-the origin of the generic name-which is curved and smooth.
MONONYCHINI LeConte, 1876
This tribe contains the single genus Mononychus Germar, 1824 with 9 species which, with the exception of the North American M. vulpeculus (Fabricius, 1801), are all Palaearctic in distribution; 3 species occur in Western Europe. All species feed on various Iris, including cultivated species and varieties, and outside the U.K. several are pests of commercially grown plants and large scale production is protected with the use of insecticides. Adult weevils bore into developing flower buds so damaging them and causing disfigured flowers; small numbers go unnoticed but the damage caused by large populations soon becomes obvious. Within the Ceutorhynchinae at least they are large weevils, about 4-5.5mm, and unique in having a single claw to each tarsus, the rostral groove is deep and extends back to the level of the posterior margin of the mesocoxae, and the anterior margin of the pronotum is deeply incised medially.