Common name:Oil beetles
Number of species:11
10 species of medium to large (10-35mm) beetles. They are named after their ability to produce a bitter tasting oil from their knee joints containing the toxin cantharadin. All are nest parasites of solitary bees and are found in a variety of habitats including grasslands, woodlands and gardens.
Three genera occur.
Meloe (8 species) are distinctive black soft-bodied beetles with very short, overlapping wing cases. Three species Meloe violaceus Marsham, Meloe proscarabaeus Linnaeus and Meloe rugosus Marsham are widespread though local. Meloe brevicollis Panzer and Meloe mediterraneus Muller are very rare and confined to a few sites. Three others Meloe autumnalis Linnaeus, Meloe cicatricosus Leach and Meloe variegatus Donovan are thought to be extinct but as two species also thought to be extinct have been found in recent years they may await rediscovery.
Lytta (1 species) very distinctive metallic green beetle known as the Spanish Fly. Very rare and only known from the Isle of Wight.
Sitaris (1 species) very distinctive orange and black beetle which is a nest parasite of Anthophora bees. Very rare and currently known from one site in Hampshire.
These beetles have a fascinating life history. The females of Meloe and Lytta dig short burrows in the soil and lay batches of eggs underground. Sitaris eggs are laid within the hosts nest hole. Each female may lay several batches totalling several thousand eggs. The newly hatched larvae are known as 'triungulins' as they have three hooks on each foot. They climb on vegetation and flowers or sit in the hosts burrow and attach themselves to passing insects. The few that survive are those taken to the nests of the host bees. Once in the nest they feed on the pollen collected by the bee for her own larva and change to a grub-like form in the process. Pupation takes place in the hosts burrow. Some species remain underground as adults through the winter ready to emerge on the first sunny days of spring. Adults are diurnal during the spring and summer except Meloe rugosus and Meloe mediterraneus which are winter active and nocturnal. Adults feed on a variety of vegetation including the leaves and flowers of buttercups (Meloe) and privet (Lytta). Sitaris adults do not feed.
All species have declined in the last 50 years due to changes in countryside management which has led to the loss of their host bees.
One further species Stenoria analis (Schaum) is known from the Channel Islands and may be found in the near future. It is a nest parasite of the Ivy Bee Colletes hederae which is a recent colonist.