Sometimes all the effort put in by solitary and social bees goes to waste because their nests fall prey to various parasites. Apart from the Nomada group of cuckoo bees (see separate page), Sphecodes bees and some bumblebees, there are plenty of other invertebrates which have an impact as well.
Monosapyga clavicornis (12mm) is also nationally scarce. The species is on the wing in May and June, to coincide with the flight period of its bee hosts Chelostoma and Osmia species. Both of these nest mainly in old holes in dead wood and females of the wasp tend to fly around dead trees, posts and stumps.
From the same family, and with red and white rather than yellow on the abdomen, is Sapyga quinquepunctata (13mm), which is also shown in the Gardens section. This is a slighly commoner species but one that is still not seen that often in the field. It parasitises similar bees to Monosapyga clavicornis but is known to use Osmia rufa, Osmia leaiana, Osmia caerulescens and the downland species Osmia aurulenta among others.
The cuckoo bees enter a nest to lay eggs, whereas one of the Bombyliidae genus called the Bee-fly (Bombylius major, 12mm excluding the long proboscis), seen as early as March hovering busily as it nectars on flowers, applies a different method. She sprays her eggs on to the ground and the larvae have to make their way into mining bee nests - a haphazard method on the face of it, but the species is common so clearly it works. This bee-fly, one of nine species in Britain, is normally seen in sunny conditions and at first sight really does resemble a bee.
Parasites on larger hosts include the Conopid fly Sicus ferrugineus (8mm), one of a fair-sized group which remarkably lie in wait near flowers and ambush their prey, using an ovipositor like a hypodermic needle to lay one or more eggs (one is usual) inside the bee's abdomen. The egg develops into a larva feeding on the insect from within. Sicus ferrugineus specialises in bumblebees and is well worth watching in action, something which can often be achieved in a garden rich in flowers. They are often seen in tandem though not always mating. Myopa pellucida (8mm) is similar in appearance but scarcer. They parasitise solitary bees in the spring.
Conops quadrifasciatus (10mm), an excellent wasp mimic seen from June to September, also lays eggs on bees but the resulting grubs parasitise the bee colony's larvae rather than the adult. Conops ceriaeformis (10mm) is another parasite on Hymenoptera seen at the same time, one that is very much local in southern England. Leopoldius signatus (10mm) is a parasite of adult social wasps in the autumn and is worth looking for on Ivy, always a good source of hosts. The modest wasp 'waist' on these species is a rarity in the world of Diptera but is seen to much greater effect with Physocephala rufipes (13mm). The bee/wasp camouflage is nothing like so clear-cut with this species, which preys on as wide a range of Hymenoptera as any of the Conopids.
With most Conopid flies the target are worker bees or wasps rather than males or queens, whereas the endoparasitic mite Parasitus fucorum (1.5mm) can regularly be seen on queen bumblebees, as in the image. This is not a pretty sight and the bee was clearly troubled by the mites, trying to wipe them off and unable initially to fly with so many aboard.
In fact the mites are hitch-hiking scavengers which are believed to live on detritus in the nest, including food, faeces or pollen. Parasitus fucorum stay on the hibernating queen through the winter and while some continue with her in the new nest she constructs, others find fresh hosts when the bee heads off to find pollen in the spring.
One Hymenoptera species which cleptoparasitises bees in particular is Gasteruption jaculator, a fairly common species resembling an ichneumon. They differ in several respects from Ichneumonidae, one of which is that the long ovipositor tends to be used for probing and laying eggs in open burrows, not drilling. The female shown above egg laying, who had to go right into the burrow to complete the job as the second image shows, was parasitising a nest in a bank containing a variety of mining bees, including Colletes fodiens and Andrena flavipes. Gasteruption assectator is not seen so often and has a much shorter ovipositor. This species goes after Hylaeus (yellow-faced) bees among others.
In passing, the mating pair of Conops quadrifasciatus is pictured on Common Ragwort (Senecio jacobaea), a designated pest species, in so far as eating it can be fatal for quadrupeds, especially horses and cattle. However, it is a valuable part of the native British flora, providing sustenance to a significant number of invertebrates, most obviously the Cinnabar Moth (Tyria jacobaeae), whose caterpillars feed on the leaves, so there is no justification for obliterating it from areas where horses do not graze.
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.