Tuesday, 31 March 2015

Violet Oil Beetle in France

Oil beetles are another one of those species that not everyone is comfortable with due to their interesting life cycle which we’ll come to.

They belong to the genus Meloe which is a large group with some 35 species of Oil beetle in Europe and 15 in France although I’m not sure how rare some of them may be and they are also somewhat understudied according to OPIE. Certainly the commonest are the Black Oil Beetle Meloe proscarabaeus and the one I find at our place the Violet Oil Beetles, Meloe violaceus, and we sure have a lot of them, so many that it’s hard not to tread on them when walking among the trees where the Lesser celandines are flowering at the moment.

Click images to enlarge

Below: Newly emerged female before putting on weight.

Below: Female having put on weight. 

Below: Recently emerged male with pronounced kinked antennae.

Below: Another male, again showing pronounced kinked antennae.

They are a flightless beetle without functional wings, and shortened elytra, (modified, hardened front wings), and they have a very interesting life cycle as mentioned.  Soon after emergence in March / April the adult beetles mate after first putting on some weight. With both the Violet and Black Oil Beetle the males have kinked antennae which they use to hang on to the females antennae with during courtship.  Once coupled they remain attached with the male being dragged around for an hour or more. The female then lays her eggs in a small hollow she digs in the soil and when these hatch the larvae, (called triungulins as they have 3 hooks on each foot), climb up the vegetation and wait on a flower head for a passing bee to settle to which they attach themselves. Very few survive but those that do and manage to hitch a ride are taken back to the solitary bees’ nest where they consume the bees’ eggs and the nutrition that has been put there. They then pupate and emerge the following year.

Below: Violet Oil Beetles coupled.

Below: Violet Oil Beetle eating Celandine.

They are classified as cleptoparasites and not actually parasites.

“”Kleptoparasitism or cleptoparasitism (literally, parasitism by theft) is a form of feeding in which one animal takes prey or other food from another that has caught, collected, or otherwise prepared the food, including stored food (as in the case of cuckoo bees, which lay their eggs on the pollen masses made by other bees). The term is also used to describe the stealing of nest material or other inanimate objects from one animal by another.”      SOURCE

Despite this behaviour which some dislike they are a good indicator of the level of solitary bee activity where they are located for without them they can’t exist.

As can be seen in the photo Oil beetles often attract small midges which feed on the oil produced by the beetle but do it no harm.

Rugged Oil Beetle Meloe rugosus,  Mediterranean Oil Beetle Meloe mediterraneus and the Short-necked Oil beetle  Meloe brevicollis are some other well known but scarcer French Oil Beetles.

If in the UK Buglife are running a survey on Oil Beetles and would appreciate your help. 



Wednesday, 18 March 2015

Horned Osmia ( Osmia cornuta )

Osmia cornuta is one of the first solitary bees to emerge in spring and as such is an important pollinator of fruit trees such as apricots, plums and almonds. Present in most of Europe, (not the north), it is a species that has disappeared from most areas of intensive agriculture, but it survives well in some urban areas, wastelands, public parks and gardens in particular areas. 

Given this living where we do in the intensive cereal lands I was extremely pleased to see a group of these about midday buzzing around the table on the patio in the sunshine. At first I thought they were Osmia bicolor with their bright orange abdomens and black head and thorax, not easy to see when they don’t settle. Anyway, a little later Lynne called me to say that a couple were kindly putting on a performance for me on the table and providing a photo opportunity. 

Please Click on images to enlarge. 

They are closely related to both Osmia bicolor the Two Coloured Mason Bee and Osmia rufa, the Red Mason Bee and they behave in much the same manner. The female builds a nest in an elongated hole, often in an old branch or some other piece of timber. The majority of the holes are between 5 to 8 mm in diameter and the nest is formed with a series of cells separated by clay partitions. Each cell contains a food reserve formed by a ball of pollen and nectar, on which an egg is laid. If the gallery is too long, a dirt cap is raised by the female to reduce its size. As a generalist pollen collector they will use what ever is available according to season, this is taken to the nest and mixed with regurgitated nectar to make the so called bee bread which is made into a pellet stuffed into the cavity.  When the cell is half full following 10 to 30 trips, the female lays an egg and builds a front wall with some clay and then repeats this until the tunnel is full with up to 15 eggs and then seals the outside with a clay plug. She repeats this for about two months building one nest after the other.

When the eggs hatch the one that were laid first which are to be females develop more slowly. When fully grown the larva spins a light brown thread cocoon and transforms into a pupa.

The bee is fully formed in late summer but remains where it is until the following spring.

The mortality rate is very high; perhaps 60% or more never get to fly and in part this is caused by Cocoxenus indagator, is which a ‘fruit fly’ and a cleptoparasite of Osmia species that lays its own eggs in the bees nest when the bee is away foraging. Having said that it’s built in to the numbers of eggs produced so nothing to be concerned about as long as the habitat requirements are met. 

Places used for nests include - Hollow stems; Galleries in walls, soft stones or soil; Gaps in window frames and drainage holes; Old galleries dug by other species of Hymenoptera; Natural or artificial galleries in timber with holes of a diameter of 8 to 10 mm; Sometimes even snail shells as with Osmia Bicolor. Galleries are thoroughly cleaned before any eggs are laid and can be used almost indefinitely. All of these locations are available at our place and with no chemicals or poisons they should go on to thrive.

Definitely one to look out for in France.