The Beewolf (Philanthus triangulum), regarded as a pest on the Continent owing to the damage it can do to Honeybee (Apis mellifera) apiaries, is a striking wasp which used to be a Red Data Book species but is commoner now and has been fairly easy to find in the South.
Visible from June to October in warm autumns, with a life as flying adults of up to six weeks, Beewolves vary dramatically in size according to sex and location, from 8mm to 27mm. Their colouring is not consistent either, with some having much more yellow on the abdomen than others.
The species probably reached its peak abundance in about 2005 when there were several aggregations on the western heaths of Surrey containing up to 10,000 nests. Since then it has declined, partly due to wet summers in 2008 and 2009, but also probably due to the crash in the Honeybee population.
This crash was caused mainly by the virus spread by the Varroa mite but these huge wasp populations may also have affected the honeybee total since one Beewolf nest up to a metre deep can contain as many as 34 cells with as many as four bees in each. The wasp eats some captured Honeybees too, and it follows that the maths on a colony of 10,000 of these wasps is astonishing.
Nests are rarely closer than 10cm to each other because of aggression. Using the legs more than the mandibles, females take three days to dig a burrow. The males can dig burrows as well, but for shelter, not to tempt the female for breeding.
The female orientates herself by flying around her nest site every time she goes on a hunting trip. The honeybees caught are embalmed with a secretion from a postpharyngeal gland prior to egg laying. This food wrapping is known to delay fungus infestation of the prey and allows less water loss in the dry areas where the Beewolf breeds. The eggs hatch in two or three days, and the larva eats all the food in its cell within a fortnight.
Philanthus triangulum sometimes capture other bee species besides Honeybees, but they are much less adaptable than a number of the 34 species of Beewolf found in the United States and studied by Professors Howard E. Evans and Kevin M. O'Neill. Wasps, Ichneumons and ants can be taken, and in Colorado and Wyoming, Philanthus pulcher took no fewer than 51 types of bee, 28 types of aculeate wasp, one Ichneumon and one Scelionid parasitic wasp.
Images © Jeremy Early. All rights reserved.
In 2013 I published My Side of the Fence - the Natural History of a Surrey Garden. Details may be found, and orders placed, via this hyperlink My Side of the Fence. In November 2015 Surrey Wildlife Trust published the atlas Soldierflies, their allies and Conopidae of Surrey, jointly written by David Baldock and me. Details are on this web page: Atlas.