Nectar in November

Insect numbers have plummeted since the first hard frosts arrived about a week ago, but ivy provides an almost unlimited supply of food for those few that are still active. The flowers continue to open well into December, although many of them will never be pollinated and produce berries. 

The first ivy flowers that open in September are almost all pollinated and produce berries that ripen in March, like those on the right of the picture above, whereas those that open after the first frosts, after insect numbers decline, are much less likely to be fruitful - like those on the left in the image above.

If you take a close look at ivy flowers on humid autumn mornings you can see the glistening drops of nectar on the surface of the exposed nectary ....

.... that are easily accessible to all insect visitors, including this small fly - one of the few insects that's still active. Although it can reach the nectar reward it doesn't make effective contact with the stamens and isn't well equipped with body hairs to transport pollen to that stubby stigma in the centre of the flower.

A few years ago observations on the vast range of insects that visit ivy flowers - including bees, wasps, flies and butterflies - prompted a group of researchers to investigate which of these was the most effective pollinator (see details of source publication at the end of this post). 

This is an ecologically interesting question because successful pollination in autumn leads to prolifically berry production in spring, providing an important food resource for migratory birds at a time when they need it most. The survival of some berry-eating birds in spring could hinge on the performance of insect pollinators of ivy in the previous autumn 

The researchers found that the most effective ivy pollinators were wasps. 

You can see here that a wasp is more hairy than is often supposed and it's just the right size to collect pollen as it feeds. It acts as a brush, picking up pollen and distributing it was it crawls across the flower surface, indulging in its taste for sweet nectar. 

So maybe we should rethink our attitude to those pesky, drowsy wasps that can be a painful nuisance once they abandon their nests in autumn and set out in search of anything sweet. Their late-season activity may well be playing a significant role in the lives of migratory birds..........

Source: Jacobs, J.H., Clark, S., Denholm, I., Goulson, D., Stoate, C. And Osborne, J.L. (2010).  Pollinator effectiveness and fruit set in common ivy, Hedera helix (Araliaceae). Arthropod-Plant Interactions 4 (1), 19-28.

For more on wasps, click here.

No ladybirds for months, then five species all at once.....

Thursday's Guardian Country Diary describes encounters with ladybirds in Weardale and Teesdale.

Back in the spring it seemed as though 2013 might be a good year for ladybirds locally - plenty of 7-spots seemed to have come out of hibernation so I anticipated a thriving population by the time their offspring hatched in summer - but it never seemed to materialise. I found a few isolated individuals of other species - notably 22-spot , 14-spot and an orange ladybird  but then last week .........

........ this huddle, near a pine plantation at Wolsingham in Weardale. It was the largest number of 7-spots I'd seen in one place all year: six that had chosen a split in a fence post as their hibernation site. 7-spot ladybirds aren't usually associated with conifer plantations but his particular row of fence posts, on the sheltered, south facing side of the plantation, as always been a good place to find other species. 

So it was no surprise to find this eyed ladybird - a conifer specialist - sunning itself on the same line of fence posts.

A small, unidentified fly with unusual up-turned antennae had even chosen to hitch a ride on it. The eyed ladybird is our largest species but ...

...... this one, a larch ladybird that shared the same fence post, is one of our smaller species ...

..... here going head-to-head with a staphylinid beetle (which it simply head-butted out of the way!)

Then, a day later at Egglestone in Teesdale I found ivy in full flower that had attracted several orange ladybirds, that were feeding on nectar.

You can see here the translucent pronotum of this species, that used to be considered scarce but seems to have increased in abundance in recent decades, supposedly because it has taken to feeding on fungi that grow on the honeydew secreted by sycamore aphids. On one occasion a few years ago I found a cluster of ten of this species hibernating on the bark of a sycamore in winter - it's certainly a species that can be added to the very small number of insects that are associated with sycamore, which has been present on these islands for around 500 years but has a very small insect fauna.

Close to the orange ladybirds on the ivy I then found a single 7-spot sunning itself on a fence post and ......

.......... scores of this very unwelcome addition to our ladybird fauna - the harlequin. The first time I saw these locally was in Durham city back in 2009, on ivy flowers at almost exactly this time of year. Harlequins are noted for their bewildering range of colour patterns but the indentations at the tail end of the elytra are also a distinctive feature, although they too vary in extent between individuals.

This group of about a dozen individuals had just hatched from their pupae and were still developing their full colours. Harlequins have a breeding season that extends well into autumn.

Some, that also seemed to be the most rotund individuals, were almost entirely black ...

..... but his was a more typical colour pattern in this population.

Finding another population of harlequins was an unwelcome discovery because this disease-resistant species is known to be a predator of our native ladybirds and can also transmit a parasite that kills other species. It also feeds extensively on eggs of butterflies and moths. Over the last decade it has spread rapidly from south east England to the Scottish border. It originated in central Asia but was introduced elsewhere in misconceived biological control programmes aimed at 'environmentally friendly' aphid control in greenhouse crops. Wherever it has been introduced it has escaped and has had a detrimental effect on native insect populations.

The predominantly black individuals seem to have blue eyes.

This was the last unhatched pupa, attached to the fence posts. At the point of attachment you can just see the remains of the larval skin, which is spiny in this species. 

Harlequin larvae also seem to have an affinity with sycamore, perhaps because of the vast supply of sycamore aphids that they find on the leaves - so it may well be that orange ladybirds will also form part of their diet too.

If you find harlequin ladybirds you can report their presence by contributing the record to the Harlequin Ladybird web site.

Grow-your-own wild bird food

Time to start feeding the birds again, which must be even more satisfying if you grow your own sunflower seed for feeding finches..............  

I noticed these magnificent giant sunflower seed heads drying in a garden at Blanchland yesterday. Made me wish I'd grown some too. 

Next year.....................