298 THE WILTSHIRE ARCHAEOLOGICAL AND NATURAL HISTORY MAGAZINE 
The Rugged Oil Beetle (Meloe rugosus Marsham) 
discovered in Wiltshire 
by Michael Darby 
I was recently asked to determine a small collection 
of beetles made by Godfrey and Michael Smith, the 
well-known lepidopterists, who live near Trow- 
bridge. To my surprise several rare beetles were 
present including Ischnomera caerulea (LL), which 
they had found in a rotten elm — its normal habitat 
— on their farm (3 specimens 5 April 1987), a 
surprising location for a species which is almost 
exclusively confined to ancient broadleaved 
woodland. But the most exciting discovery was 
undoubtedly a single specimen of the Rugged oil 
beetle, Meloe rugosus Marsham, picked from a 
Sainfoin plant on Bratton Hill on 24 September 
1984. This rare beetle, not previously recorded from 
Wiltshire, is classed as Red Data Book 3 being 
known from only a handful of southern localities, 
and none at all since 1904 when a single female was 
noted at Upper Lypiatt in Gloucestershire. 
Interestingly a second specimen turned up on 12 
December 1984 at Broadway in Worcestershire 
(Whitehead 1987) and since then there have been 
two further records. 
Meloe rugosus Marsham 
M. rugosus is immediately distinguishable from 
the Black Oil Beetle, M. proscarabaeus L., the only 
other member of the family recorded from the 
county, by virtue of its smaller size (max. 18mm), 
matt greyish-black colouring (never shiny), and the 
proportionately much broader pronotum. Another 
factor aiding identification is the time of 
emergence. M. proscarabaeus is always found in the 
Spring whereas M. rugosus does not emerge until 
September and has been recorded to breed 
throughout the winter (Whitehead 1990). Late 
emergence may account for the beetle having been 
overlooked. 
What marks out oil beetles as of particular 
interest is their fascinating life history. All are 
parasitic on bees of the genera Andrena, and 
Anthophora. In most species the female beetle, after 
making some small holes in the ground, deposits in 
them from two to four batches of tiny yellow eggs, 
some thousands at a time, glued together. After an 
interval of three to six weeks these hatch out into 
tiny larvae with long legs terminated in a single 
claw. The larvae climb on to low plants, chiefly 
Ranunculaceae or Chicoraceae, from which they 
attach themselves to visiting bees, sometimes in 
large numbers. Once in the bee’s nest they devour 
the bee’s eggs and change into a second form, 
arched, cylindrical and with toothed mandibles 
and stout legs. These feed on the food deposited by 
the bee for its young. After a time this second form 
changes its outer covering, which is not entirely 
shed but remains wrinkled and attached so 
looking like a ‘false pupa’. From this a third form 
emerges like the second, before the adult beetle 
finally appears usually in the early Spring. 
M.rugosus, however, differs from this pattern in that 
adults are able to survive the winter even when 
temperatures drop to as low as —15°C. Furthermore, 
Whitehead’s observations suggest that it favours 
the bee Anthophora plumipes exclusively as its host 
species. 
What gives oil beetles their name is the ability 
to secrete when disturbed an oily substance called 
cantharidin from their joints. This is highly toxic 
and acts as an anti-predation device. (Ramsay, 
2002). However, cantharidin has also been recorded 
as strongly attractive to species of midge 
(Atrichopogon spp.) and anthicid beetles, which suck 
the blood from the adult beetles. 
Nine species of oil beetle have been recorded 
from Britain but nearly all are now extinct or in 
serious decline. Ramsay suggests that the reasons 
are unclear but it is possible that climatic change, 
The Old Malthouse, Sutton Mandeville, Salisbury SP3 SLZ 
