Oil beetle  (Meloe proscarabaeus)

Vulnerable. This species has declined drastically in recent years (3).

The oil beetles are a family of beetles that share a fascinating life-cycle in which the larvae are parasites of certain bees or grasshoppers (2). This species, Meloe proscarabaeus is bluish black in colour with a long swollen abdomen(2), which is particularly pronounced in females when they are producing eggs. Females are usually much bigger than males (4).

Only three of the nine oil beetle species native to Britain remain, and the number of sites supporting these species has declined drastically. This beetle was once common (3), but is now restricted to the west of Britain (4). It is also found in Europe (2).

In Europe, the black oil beetle shows a preference for low-lying flat terrain (2). In Britain it is found on heaths, coastal cliffs and moors (1).

Oil beetles have fascinating life-cycles. The larvae are parasites of a number of species of ground-nesting solitary bee. Towards the end of spring, female oil beetles dig burrows in the ground close to colonies of host bees, into which they lay around 1000 eggs. These eggs usually hatch the following year in order to coincide with the emergence of the bees. The oil beetle larvae (known as tringulins) are very active, and climb up onto flowers where they wait for a host bee. They attach themselves to the bee, and if they are lucky and attach to the right type of species they will be flown to the host’s burrow, where the tringulin oil beetle turns into a grub-like larva, and develops, feeding upon the pollen stores and eggs of the host. The larva pupates and the resulting adult beetle spends the winter inside the host’s burrow before emerging the following spring (4).

The reasons for the decline of this species may reflect declines in host bee populations.

Buglife, the invertebrate conservation trust, is currently running the Oil Beetle Project, which aims to establish the current range of Britain’s remaining oil beetles and to carry out research into their life-cycles and ecology in order to guide conservation actions targeted at these beetles (4).

For more on the Buglife Oil Beetle Project and for details of how to help see:
http://www.buglife.org.uk

• Abdomen: in arthropods (crustaceans, insects and arachnids) the abdomen is the hind region of the body, which is usually segmented to a degree (but not visibly in most spiders). In crustacea (e.g. crabs) some of the limbs attach to the abdomen; in insects the limbs are attached to the thorax (the part of the body nearest to the head) and not the abdomen. In vertebrates the abdomen is the part of the body that contains the internal organs (except the heart and lungs).
• Larvae: stage in an animal's lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
• Parasites: organisms that derives food from, and live in or on, another living organism at the host’s expense.
• Pupates: Pupation is the the process of forming a pupa, the stage in an insect's development when huge changes occur that reorganise the larval form into the adult form. In butterflies the pupa is also called a chrysalis.

1. National Biodiversity Network Species Dictionary (September 2003): http://www.nhm.ac.uk/nbn/
2. Harde, K.W.(2000) A field guide in colour to beetles Silverdale Books, Leicester.
3. English Nature. Undercliff Matters. (October 2003): http://www.english-nature.org.uk/about/teams/team_photo/Undercliff%20Matters%20Issue%201.pdf
4. Buglife Oil Beetle Project (October 2003): http://www.buglife.org.uk/html/oil_beetle_life_cycle.htm