Banking on bees

Much has been written about the importance of sunny banks for invertebrates - they are often included (sometimes as 'beetle banks') in habitat management plans and as sometimes appear as recommended features related to mitigation of various types of site development. There is much about this and other aspects of habitat management for invertebrates in e.g. the excellent Kirby (2001), but I want to focus on a local example of a feature that has just this function, albeit unintentionally - a south-facing bank alongside the footpath leading to the front of a nearby church in Hampshire, southern England.

The south-facing bank in a nearby churchyard

This is not a huge feature - it's around 10 metres long and no more the around a metre high at most (as the path rises, the bank gets lower until it merges with the rest of the churchyard). However, there are nearby flowers as pollen sources, plus small bare patches of light soil, just right for burrowing. It is also south-facing and hence sunny and warm - this is key as the north-facing slope on the other side of the path does not support the range of pollinators described below. A couple of days ago, these were found and photographed during less than an an hour on a sunny day in what is currently proving to be an unusually warm spring (I'll leave out discussion of climate change on this occasion). So, what did I find?

The bee-fly Bombylius major

The commonest bee-fly in the UK, B. major can be identified by its broad, dark wing-bands (not to mention the long proboscis characteristc of this gorup) and parasitises a number of solitary bee species - so, as well as being a herald of spring, it's also an indicator that there are bees around somewhere. However, in this case, a indicator of bee activity wasn't needed - I just needed to look at the grassy bank to see a flurry of activity.

Andrena cineraria - an attractive black and white ground-nesting species

The most obvious bee species was A. cineraria - I spotted around 15 at one time (it's difficult to be more precise as they rarely stop flying around), including some using entrance holes to burrows, plus brief 'tussles' between pairs of individuals. In some places, this species nests in huge aggregations of thousands of females and attendant males (Baldock, 2008) and I wonder if these 'tussles' are aggressive encounters related to access to nest-burrows, or are failed mating attempts - they are too fast to be certain about the sex of the participants. Of course, where one species is found, its parasites often follow - in this case the cleptoparasite Nomada lathburiana which can be very numerous in the large aggregations mentioned above. Cleptoparasites are also known as 'cuckoo bees' as they lay their eggs in nests of other bee species, their  larvae feeding on the food provided for the host larvae. Needless to say, I was on the lookout for N. lathburiana and it wasn't long before I saw one investigating the entrances to A. cineraria nests.

Nomada lathburiana showing the yellow spots and bands seen in several species of this genus.

However, although this was an interesting find, there were other bee species, including a small (aroung 6mm long) fairly dark bee that was extremely difficult to photograph due to its rapid darting flight and tendency to re-launch whenever I got near. However, I did manage to get a shot and it turned out to be another cleptoparasite, N. flavoguttata.

Nomada flavoguttata - note the reddish-brown bands on the abdomen, including a pair of tiny yellowish dots (the species name means 'yellow spots').

Although possibly not that familiar, this is a fairly common species which parasitises several small Andrena species. This is important because at this point I hadn't seen any small Andrena, only A. cineraria, so I continued looking. Then, among the flurry of black & white bee bodies, I noticed a likely candidate - a small bee crawling around under the leaf litter. Again, photography was tricky as, when on the ground, it crawled underneath leaves, and flew rapidly away as soon as it emerged - definitely camera-shy! However, I did get the following picture, and (from other views, including while feeding on dandelion Taraxacum flowers) enough detail to identify it as A. minutula, the commonest of several similar species and a known host of N. flavoguttata.

Andrena minutula crawling underneath leaves.

Two host-parasite pairs was good for an hour's work, but there was more bee-biodiversity to be found as I saw another Andrena species exiting a burrow.

Andrena flavipes flying away from its burrow

A. flavipes is identified by the pale abdominal hair-bands and orange-yellow pollen-hairs in the hind tibiae, and like A. cineraria, can be found in large nesting aggregations. It also has its own cleptoparasite, N. fucata although I could not find this although it is present at almost all of its host's nest sites - more hunting will be required.

So, I hope these observations have reinforced the importance of sunny banks as invertebrate habitat - including for our often-declining, yet essential, populations of pollinators. If you have a little spare space in your garden or another piece of land, why not add a little bank - even a small one will attract invertebrates.

An insect's-eye view of the bank with A. cineraria flying overhead.

References

Baldock, D.W. (2008). Bees of Surrey. Surrey Wildlife Trust, Pirbright.
Kirby, P. (2001). Habitat Management for Invertebrates: a Practical Handbook (revised reprint). RSPB, Sandy.