Wasps and cuckoo bees

Posted: Tuesday 8 May 2012
by Richard Jones

[...] as soon as the sun leaks through the cloud, I latch onto any movement in the garden. I’m relieved that, today, it’s wasps and bees.

Cuckoo bee, Nomada - photograph by Richard Jones

I’m getting mixed messages — from my own eyes, and from blog and twitter feeds around the country. It’s the time of year when everyone is bemoaning the non-arrival of spring. Or that it arrived too early and has been washed out.

My early delight at seeing bee-flies and male orange-tips in March has been dampened by the incessant rain. Now the swifts are a week late. I don’t know if they've got wind of the bad weather ahead of them; it’s an unprecedented omen of gloom perhaps.

So as soon as the sun leaks through the cloud, I latch onto any movement in the garden. I’m relieved that, today, it’s wasps and bees.

The first queen social wasp of the year, Vespula vulgaris, is finally hawking about the hedge. I often judge whether it’s a good or bad year for insects by the number of late summer wasps flying. This year I’m expecting far fewer than usual. Late April and early May are nest-founding weeks, as each queen, working alone, has to scrape and chew wood to make paper pulp for the golf-ball-sized embryo nest, lay her eggs and forage for insect prey to feed any grubs that manage to hatch in the downpours. Her flying and foraging time is limited in bad weather, her nest and brood are vulnerable to flooding, or at least damp and mould if it is wet and cold. This is a vital colony-forming window of opportunity; wet springs spell disaster for these sun-loving insects.

Bees too, especially the large number of ground-nesting solitary species, are prone to population crashes if the weather is against them. They cannot visit flowers in the rain, and their tunnel nests are liable to get waterlogged.

There are precious few solitary bees out in the garden today, but I have seen a couple of cuckoo bees — Nomada species. Often mistaken for wasps because they are virtually hairless, shining and marked with striking black and yellow bars, they do not make nests of their own — they invade the nests made by others. Just like the bird that lays its eggs in warbler nests, to be adopted, fed and cared for by the hapless parent warblers, cuckoo-bees creep into the underground nests of their hosts and lay their eggs in the cells ready stocked with pollen and nectar cake. When the cuckoo grubs hatch, they devour the host egg or maggot along with the laid-in food.

Many solitary bee species have particular cuckoo parasites attached to them and a measure of local biodiversity and ecological health can often be judged from the number of these cleptoparasite species at a given site. The parasites need a large and viable colony of their particular hosts if they are to have their own viable population. But they are even more vulnerable to weather-related declines if their hosts are brought below a certain density threshold by the pressures of their own flower-foraging limitations.

Just as I may have to wait until September to get a measure of local wasp abundance (or lack of it), so too I may have to wait until next year to gauge the effects of a wet April on my local cuckoo bees.

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oldchippy 09/05/2012 at 18:00

Hello Richard,I saw my first swift today here in
Ewell, it's the first since 31th July last year.How do they know when it's the end of July and time to leave.


Welshonion 09/05/2012 at 18:30

They leave as soon as their young are fledged.  They never land except to breed.

Richard Jones 21/05/2012 at 09:21

The swifts finally arrived on 11th May, at least a week later than usual. Pah. Fairweather travellers.