Ants in the compost bin

 We've been composting garden and kitchen vegetable waste in 'Dalek' bins like this for decades, but this year was the first times that we've had one taken over by nesting black ants. 

They moved in during those unusually cold weeks of early summer, probably because the warmth of decomposition in the bins provided the only location in the garden with enough heat for them to breed.  Textbooks say that they need a temperature of 10C to become active and 20C to raise a brood.

Watching their progress in the bins has been fascinating because the temperature inside rises very rapidly when the sun comes out and falls equally rapidly on dull wet days and in the evening, so they seem to be constantly moving their brood around to the optimum positions in the bin. At one point I thought they had left, but it seemed that they just moved their larvae and pupae deeper into the compost, in a cooler part of the bin. They shift their brood with remarkable speed when I lift the lid and light floods in - they can move a couple of hundred pupae, by carrying them in their jaws, in a few minutes.

Their larvae are translucent, but as they  pupate they spin a silken coat.

Lately, winged males have started to hatch so before long a queen will take to the air, followed by a swarm of males on the nuptial flight. After mating she will start a new nest, while most of the males will become food for swifts that swoop over the garden. 

Flying black ants

My daughter and her partner have a raised flower bed in their garden near Cambridge, built from old railway sleepers, and yesterday large numbers of the alate (winged) form of black ants emerged from their underground nest, for their nuptial flight. 

They swarmed on a day of classic flying ant conditions - hot, almost windless and sultry - and several hundred took to the air in the space of about fifteen minutes. These were either males or new queens, which would shed their wings and found a new colony after they had been fertilised.

These spectacular flights of black ants provide a valuable food source for birds. Fortunately there were still swifts, swallows and house martins flying around the village, be benefit from this sudden abundance of food. 

One interesting aspect of this event was that the winged ants seemed to be under attack from the much smaller workers from the moment they appeared above ground. The smaller ants constantly harassed the alates, nipping at their head and wings with their jaws,  until the took to the air. Once the winged forms were all airborne the workers disappeared below ground again.

A few of the winged forms seemed to be weakened or killed by the attacks.

In this image you can see a worker gripping an alate's wing with its jaws.  

Ivy - the all-year-round carbon dioxide fixer

Ivy's flowers provide a wonderful nectar and  pollen resource for insects in autumn (see some examples at the bottom of this post) and its berries are a vital food  resource for migrant birds in early spring, but it also has another important attribute with more general implications.

As an evergreen that stores carbon in its woody trunk, ivy is an all year-round carbon dioxide fixer, constantly removing the gas from the atmosphere. In that respect it contributes towards combatting the build-up of carbon dioxide in the atmosphere, which is the underlying cause of global climate change.

Deciduous trees like this ash have a short growing growing season in our seasonal climate. It comes into leaf in May and sheds its foliage in September, so for about half the year it fixes no carbon dioxide at all. But when it supports a luxuriant growth of ivy the two organisms together fix carbon dioxide 365 days a year.







































The combined efforts of an ash tree with ivy cladding are likely to be more effective at fixing atmospheric carbon dioxide than an ash tree alone.

The tangle of  thick, woody ivy stems on this sycamore are as effective a store of carbon as the tree's trunk.

Ivy can even turn a dead tree into a carbon dioxide fixing pillar of evergreen foliage, as it did with this dead oak at Egglestone in Teesdale a few years ago. Even better, in autumn this stump became a tower of flowers, humming with insects that came for the nectar and pollen. In spring it was covered in berries.

Another example, at Wolsingham in Weardale.

Sadly, there are still plenty of ivy-haters around who are convinced that ivy is a parasite (it isn't, it just uses trees for support). They'll usually also advance the argument that a top-heavy mass of ivy is likely to bring trees down in winter gales, but most trees that are felled in this way are moribund anyway and topple because they have already been weakened by root-rotting fungi, not by ivy. Logically, a good cladding of well-rooted ivy stems is more likely to anchor a shaky tree, delaying its demise. 

The fact that trees that have been killed by fungi often have a healthy covering of ivy suggests that it might well be resistant to some of the fungi that kill trees.

From all of this you might have gathered that I'm something of an ivy enthusiast - not least because of the insect fauna that its flowers attract in autumn. All of the pictures below were taken in a few minutes late last October on another ivy clad tree just across the road from the oak-clad stump pictured above. 

Ants and Aphids

This black ant, with its lethal-looking jaws outstretched, isn't about to eat the aphid - it's farming it.

This is a mutually beneficial arrangement. The ants 'milk' their herd of aphids, collecting the sweet honeydew that the aphids excrete as they feed on plants sap, and in return the aphids are protected by their ferocious minders. The ants stroke the aphids with their antennae to encourage them to produce a continuous supply of honeydew.

Apparently the relationship even extends to ants picking up young aphids in their jaws and carrying them to uninfested parts of the plant, where the aphids rapidly breed and establish a new 'herd'.