This nice shiny green beetle is Polydrusus formosus [Soortenregister] from the family of Snout beetles, or Weevils (Curculionidae) [Käfer Europas],[Kerbtier.de].
Some publications use its older scientific names [Soortenregister]:
- Polydrusus splendidus (Herbst, 1784)
- Polydrusus sericeus (Schaller, 1783)
CONTENTS
1. Distribution
2. Behaviour
3. Plant relations
4. Prey relations
5. Identification
1. DISTRIBUTION
P. formosus is a common beetle in the Netherlands and in the garden.
It prefers wooded borders, parkland, gardens and wastelands, anywhere as long as its host plants are there [UK Beetles].
2. BEHAVIOUR
2.1. ACTIVITY
Active from April to August [NatureSpot].
The adult animals browse leaf and flower butts, young leafs and blossoms.
2.2. DEVELOPMENT
Adults lay their eggs single or in small clusters [UK Beetles], in the bark or on the leafs of the host plant [NatureSpot]. The larvae live in the ground and feed on the plant roots [NatureSpot],[UK Beetles]. In autumn their development is complete and they overwinter as pupa in the ground [UK Beetles] and hatch in spring [NatureSpot].
2.3. DEFENSE MECHANISMS
When the beetle feels threatened it will drop and pretend to be dead.
3. PLANT RELATIONS
The beetle uses a number of host plants [NatureSpot],[UK Beetles],[Pinski et al. 2005],[Hillstrom et al. 2010]:
| Plant | Presents |
| Maple (Acer) | – |
| Alder (Alnus) | vicinity |
| Birch (Betula) | vicinity |
| Hazel (Corylus) | garden |
| Hawthorn (Crataegus) | – |
| Apple (Malus) | garden |
| Poplar (Populus) | vicinity |
| Prunus | – |
| Pear (Pyrus) | – |
| Oak (Quercus) | vicinity |
| Willow (Salix) | – |
| Elm (Ulmus) | – |
The species has a large preference for Birch (Betula) [Pinski et al. 2005],[Hillstrom et al. 2010], which increases fecundity substantially [Pinski et al. 2005],[Hillstrom et al. 2010]. In lab circumstances this resulted in females with access to Birch would lay an average of 29 egg a day, whereas the females that were feeding on Maple laid only 2 eggs a day on average [Pinski et al. 2005].
Adults are known to cause damage on fruit butts, shoots and blossoms in fruit trees but do not become a pest. At least on apple, the damage can result in cork-like scars [Alford 2014].
4. PREY RELATIONS
The species is hunted by the following predators:
Diggerwasps
(HYMENOPTERA, Crabronidae)
| Genus | Soort |
|---|---|
| Cerceris [Alford 2014] | – Cerceris arenaria [Bohne 2014] |
In de tuin zijn de volgende rovers geobserveerd:
| Family | Genus / Species |
|---|---|
| Diggerwasps (HYMENOPTERA, Crabronidae) | Cerceris – Cerceris arenaria |
5. IDENTIFICATION
A number of similar looking beetles reside in the Netherlands, which can make determination difficult [Soortenregister].
5.1. EGGS
Freshly deposited eggs are bright yellow in color and gradually fade to white [Pinski et al. 2005].
They are ±0,5×0,3 mm in size [Pinski et al. 2005].
5.2. LARVAE
Larvae are about 7 mm in length, are C-formed with a cream-white color with brown head [Alford 2014].
5.3. ADULTS
Adults are 5 to 8 mm [Alford 2014],[Sleeper 1957] in length.
Female + Male
- Eyes located to side of head
- Neck shield edge without hairs
- Neck shield edge straight, doesn’t cover eyes
- Shoulders clearly wider than neck shield and rounded corners
- Antennae implanted near side of the snout
- Antennae don’t extend over back edge eye when it would lie flat to the side of the head
- Antennae segments III to VII much longer than wide
- Area between eyes narrower than area between antennae holes
- Black body entirely covered in dense and evenly spread metallic green round scales (the scales can wear revealing black spots or entire black area’s)
- Antennae and legs red-yellow to red
- Legs with barely visible teeth
- Antennae holes on snout black
- Large eyes that barely protrude
- Elytra (wing covers) near tip normally develop and tightly adjoined
- Snout tip weakly widened
Male
- Backside hind-shins with long hairs
Males in this species can be identified based on the following characteristics [Sleeper 1957]:
- apical ridge on last sternum (segment underside)
- apical cluster of long hairs on shin ventrally
As I couldn’t find any comparison material and the photo evidence quality is not that great I’m not 100% sure, but it could be a male.
Literature
Alford 2014 Alford, D., 2014. Pests of Fruit Crops. Boca Raton: CRC Press, https://doi.org/10.1201/b17030Bohne 2014 Bohne, G., 2014, iNaturalist: observation predator relation Cerceris arenaria ➧ Polydrusus formosus
Hillstrom et al. 2010 Hillstrom, M. L., Vigue, L. M., Coyle, D. R., Raffa, K. F., & Lindroth, R. L., 2010. Performance of the invasive weevil Polydrusus sericeus is influenced by atmospheric CO2 and host species. Agricultural and Forest Entomology, 12(3), 285-292.
Käfer Europas Die Käfer Europas, Ein Bestimmungswerk im Internet, Herausgegeben von Arved Lompe, Nienburg/Weser, Begründet im September 2002
Kerbtier.de Kerbtier.de Käferfauna Deutschlands
NatureSpot NatureSpot - Recording the Wildlife of Leicester & Rutland
Pinski et al. 2005 Pinski, R. A., Mattson, W. J., & Raffa, K. F., 2005. Host breadth and ovipositional behavior of adult Polydrusus sericeus and Phyllobius oblongus (Coleoptera: Curculionidae), nonindigenous inhabitants of northern hardwood forests. Environmental Entomology, 34(1), 148-157.
Sleeper 1957 Sleeper, E. L., 1957. Notes on North American species of Polydrusus Germar. The ohio Journal of science, 57(3), 129-134.
Soortenregister Nederlands Soortenregister
UK Beetles UK Beetles
Citation
Krischan, O.R., 2025. Polydrusus formosus. Kerfdier, www.kerfdier.nl. Accessed on 18 April 2025.
