This nice shiny green beetle is Polydrusus formosus from the family of Snout beetles, or Weevils (Curculionidae) [1, 2].
Some publication use its older scientific names :
- Polydrusus splendidus (Herbst, 1784)
- Polydrusus sericeus (Schaller, 1783)
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 .
Active from April to August .
The adult animals browse theleaf and flower butts, young leafs and blossoms.
Adults lay their eggs single or in small clusters , in the bark or on the leafs of the host plant . The larvae live in the ground and feed on the plant roots [3,6]. In autumn their development is complete and they overwinter as puppa in the ground  and hatch in spring .
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 [3,6,8,9]:
The species has a large preference for Birch (Betula) [8,9], which increases fecundity substantially [8,9]. 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 .
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 .
4. PREY RELATIONS
The species is hunted by the following predators:
|Cerceris ||– Cerceris arenaria |
In de tuin zijn de volgende rovers geobserveerd:
|Family||Genus / Species|
– Cerceris arenaria
A number of similar looking beetles reside in the Netherlands, which can make determination difficult .
Freshly deposited eggs are bright yellow in color and gradually fade to white .
They are ±0,5×0,3 mm in size .
Larvae are about 7 mm in length, are C-formed with a cream-white color with brown head .
Adults are 5 to 8 mm [4, 7] 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 develope and tightly adjoined
- Snout tip weakly widened
- Backside hindshins with long hairs
Males in this species can be identified based on the following characteristics :
- richel op het laatste sterniet apex (segment onderzijde)
- Groepje lange haren op onderhelft achterzijde achterscheen
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.
References1 Die Käfer Europas, Ein Bestimmungswerk im Internet, Herausgegeben von Arved Lompe, Nienburg/Weser, Begründet im September 2002
2 Kerbtier.de Käferfauna Deutschlands
3 NatureSpot - Recording the Wildlife of Leicester & Rutland
4 Alford, D. (2014). Pests of Fruit Crops. Boca Raton: CRC Press, https://doi.org/10.1201/b17030
5 Nederlands Soortenregister
6 UK Beetles
7 SLEEPER, Elbert L. Notes on North American Species of Polydrusus Germar (Coleoptera: Curculionidae, Brachyderinae): 17. A Contribution to the Knowledge of the Curculionoidea. 1957.
8 PINSKI, R. A.; MATTSON, W. J.; RAFFA, K. F. Host breadth and ovipositional behavior of adult Polydrusus sericeus and Phyllobius oblongus (Coleoptera: Curculionidae), nonindigenous inhabitants of northern hardwood forests. Environmental entomology, 2005, 34.1: 148-157.
9 HILLSTROM, Michael L., et al. Performance of the invasive weevil Polydrusus sericeus is influenced by atmospheric CO2 and host species. Agricultural and Forest Entomology, 2010, 12.3: 285-292.
10 Dr. Guido Bohne, 2014, iNaturalist: observation predator relation Cerceris arenaria ➧ Polydrusus formosus