Catching the wind

The last couple of weeks have witnessed increased activity of garden ants. It is the season when winged ants (males and queens) take to the air forming swarms. Today I noticed groups of queens emerging from a nest in the garden. The queens climbed over the plants, warmed up their wing muscles and took to the air. They often land straight away unless they can get high enough and ride the breeze. This was that this winged ant was doing, with head and antennae outstretched, it checked if it was the right time to fly. The dark clouds in the background are also typical of flying ant days, as the prefer stormy, warm weather to emerge.
The lucky ones will mate in the air and come back to the ground, lose their wings and find a suitable site to start a nest. Many will perish though, eaten by birds or spiders.
 If you notice flying ants where you live, you can submit your record to the Flying Ant Survey, organised by the Society of Biology. It only needs a couple of minutes to fill the form.

Queens and kings on the wing!

We've enjoyed a whole week of warm weather and no rain. Today, garden ant queen, Lasius niger,  that had already lost its wings, was running on the pavement, and on my local wildlife garden, nervous workers on the path made me look closer. When new winged queens and male ants are ready to emerge, workers follow them run frantically about. And emerging they were, for at least the third time this year, many queens and smaller numbers of male ants. Some queens were trying, unsuccessfully to fly straight from the ground, others, like the one above, reached for a higher point, to get a better chance to take to the wing.

Winged ant queen, Lasius niger, revving its wings on the ground

The couple of queens above started climbing a fence post while the workers followed them. Although many winged ants will eventually take to the sky, where they find their mates, a Zygiella x-notata web hung with entangled winged ants on top of this fence post. That spider is going to have a super dinner tonight.

 I have never seen flying ants this late in the year, have you seen any winged ants recently? The Society of Biology is carrying out a Flying ant Survey, where you can submit your records.

Ants tending aphids

Ants have a sweet tooth. They gather nectar from flowers, buds and nectaries but also farm animals to obtain their sweet honeydew. These farmed animals are scale insects and aphids. Ants tend the aphids (above), protect them from their predators and parasites and keep them together for easy "milking". To obtain the honeydew produced by aphids, ants stimulate them with their antennae, after which the aphid will secrete a droplet of sugar rich liquid. These ants are tending groups of aphids on an Iris leaf. To soften the built-in flash light I put a piece of kitchen paper in front of it, holding it with my left finger.

Birds and ant swarms

In July and August, typically in sunny days after rains, swarms of reproductive Black Garden Ants (Lasius niger) - winged queens and males - emerge from their nest to mate and start new colonies. Workers also come out en masse and run around the entrance of the nest, looking agitated. I had often noticed this and wondered why do workers did this, until yesterday, watching a Blackbird feeding on the winged ants coming out of their nests, realised why. The Blackbird run close to the entrance, fetched a winged ant and run away. The bird repeated this several times and was obviously being stung or sprayed by the ants around the nest, but still wanted to feed and its back-and-fro behaviour was evidence of the - at least partial - success of the frantic workers keeping predators at bay. Winged ant have many predators. Some casually feeding on the winged ones, others opportunistically making use of a plentiful, although ephemeral, bonanza. A range of birds fall in the latter category, starlings and sparrows feed on the winged ants - sometimes using fly-catcher techniques - and seagulls have been seen feeding on them up in the sky. While reading a paper on this, I remembered that last year, on the day the ants emerged, I looked up in the sky and saw many small flying things and thought they might be the flying ants. When I looked more closely I saw they were seagulls, and was surprised at how many there were, well over a hundred, soaring very high up. I took a shot (below) and forgot about it. They were most likely feeding on the winged ants that had been carried high by thermals in their swarming mating flight.

Seagull flock feeding on swarming ants (26/07/10)

This is the nest in the bottom right hand corner of the top photo

Workers around a nest with winged ants emerging (26/07/10)

Reference

James Baird and Andrew J. Meyerriecks (1965). Birds Feeding on an Ant Mating Swarm. The Wilson Bulletin, 77 (1), 89-91.
Gilbert S. Grant (1992) Opportunistic Foraging on Swarming Ants by Gulls, Shorebirds, and Grackles. The Chat, 56, 80-82.

Queen ant makes spider dinner

I have come across queen garden ants (Lasius niger) for a week. The first one, a wingless one wandering on the garden checking every little crack on the cement eager to start digging her nest. She was quick and the light conditions weren't ideal, so, reluctantly, I moved her to a white bowl for a portrait (above). Yesterday, queens and males were emerging en masses from nests on the side of the street pavements in the afternoon, ready to start their nuptial flights.
The males are similar in size to workers, the queens, double their size and with a much larger abdomen.

Male garden ant

 I even got a mating pair, with the female dragging the male about and both flying away:

Mating ants (the male's antenna can be seen on the right hand side of the queen)

The queen ants will usually mate once in this flight and then land and dig their nests and live underground the rest of their long lives, the males will die shortly after. I say the queens, but I should have said the lucky queens. Most of them will actually die before they hit the ground again, eaten by swifts, swallows, gulls or sparrows. Others will contribute to a spider bonanza. Hundreds of aphids and some ants could be seen yesterday and today covering the webs of the missing sector spider (Zygiella x-notata) on railings. One queen wandered on my conservatory wall and fell on the disorganised cobweb of a Steatoda bipunctata spider, who quickly approached the ant (maybe biting it?) and retreated to the corner of its web. A few minutes later the queen had stopped struggling, and the spider came out for his dinner.

Steatoda bipunctata with dinner

The spider drags the queen ant to its retreat (notice the screw head for scale).

Ants as scavengers and herders

So far I have overlooked two important aspects of garden ant foraging behaviour, mainly due to the lack of suitable photos. Yesterday, I spotted a strange large insect walking on the concrete yesterday, when I got closer I realised it was actually a dead bluebottle being dragged by a garden ant (Lasius niger). Another ant run frantically back and forth, but a single one seemed to do most of the work. The strength of an ant is quite formidable, able to lift or drag objects much heavier than themselves. This illustrates the role of ants as scavengers. Any dead animal will either be dragged to the nest or bits of it will.

The second aspect is one of the most surprising of ants - showing their adaptability -  but also a reason why they are hated by many gardeners: their role as aphid herders. Ants behave as farmers with their aphids and will try to keep the numerous aphid predators at bay as well as milking their honeydew. This is considered a mutualistic relationship and aphids also benefit from the behaviour. Even when aphid predators are excluded, aphids multiply faster in the presence of ants. The photo, taken today, shows two garden ants stimulating Elder Aphids (Aphis sambuci) to excrete their honeydew. Elder aphids form very compact groups on tender growing stems of Elder.

Ants helping plants: extrafloral nectaries

In the last couple of weeks I have posted about ants affecting plants negatively one way or another: taking nectar from flowers but failing to fertilise the plant; farming scale insects and defending them from their predators. Ants, however, also have mutualistic relationship with plants. Take cherry trees. As their green cherries are growing, their young, tender leaves are at their juiciest. Many caterpillars and other herbivorous insects would love to have a go at them. But cherries have a sweet way to call for bodyguards: they secrete nectar in red floral glands at the base of each leaf - also called extrafloral nectaries. These are irresistible to black garden ants (Lasius niger) (above) and they secrete nectar in small quantities so they encourage ants to scout around the tree to find the next leaf. Should they encounter a caterpillar trying to get to the leave, or an insect land on it, the ants act aggressively like they would do to defend aphids or scale insects, and keep the insects at bay. Nectaries are produced by a large diversity of flowering plants and experiments have demonstrated that if ants are excluded from a nectary bearing plant, the plant is rapidly damaged by herbivorous insects. In the American black cherry, nectar production in nectaries is seasonal and it is precisely timed to the period when tent caterpillars are small enough to be able to be predated by an ant. When ants are disturbed by an insect, they immediately attacked the insect and if small, they carried it back to their nest. This seasonal match between nectar production and caterpillar attack suggests that the main function of nectaries is ant attraction, as a deterrent from herbivorous caterpillars.

An ant inspecting the nectary, a glistening drop of nectar in the middle of it. Smaller nectaries are also present at the end of each serration in young leaves.

Two ant on nectaries.

More information
Tilman, D. (1978). Cherries, Ants and Tent Caterpillars: Timing of Nectar Production in Relation in Relation to Susceptibility of Catepillars to Ant Predation Ecology, 59 (4) DOI: 10.2307/1938771

Ants score again

Frustrated by not getting the shot of the Bombus terrestris queen chewing the comfrey flowers the other day, I check the comfrey quite often. I am surprised - OK, not much I must say - by an ant (Lasius niger) walking on the flowers and entering them using the convenient hole made by the bumblebee queen. So, ants are also secondary nectar robbers!

Ant peeks into the hole

Getting in

and she is in sucking the lovely sweet nectar...

Ant vs. ladybird

I illustrated in yesterday's post than ants tend scale insects for their honeydew. My orange trees have many scale insects and numerous ants tirelessly tending them. Ladybirds like scale insects too, but for entirely different reasons. Yesterday, I took some photos of a 7-spot ladybird munching on scale insects. Ants, of course, do not like this, and today I managed to witness an ant (or ants) attacking a 7 spot ladybird. The ant was very persistent. It was quite windy, and in several occasions, the ant was blown away only to return to the ladybird a little later. To my eyes, the ladybird defence was passive, she tucked her legs under her body and didn't move much, relying on its shiny and slippery elythra for protection. The ant had her jaws wide open and her abdomen often curved underneath its body, as if it was spraying the ladybird with formic acid. She went for the gap between the thorax and abdomen in several occasions, trying to get a place to bite. After the struggle, the ladybird remained in the tree. There was a Harlequin ladybird on the same tree near some scale insects and I will keep a watchful eye for ant attacks on her too. It was quite challenging to get shots with the wind and the ladybird being in between the foliage, but a series follows.

If you click on this photo you might see the wide open jaws of the ant

Looking for a weak spot

From the back

Curled up abdomen

Looking for the ladybird legs

Harlequin and scale insects

Ants in my plants

The Black garden ant (Lasius niger) is a very successful ant species. Part of their success lays in their adaptability. They are opportunistic in their choice of food: they feed on dead animals, nectar and pollen, seeds and honeydew. They are farmers, tending for aphids and scale insects and collecting the honeydew they secrete in exchange for protecting them from parasites. At the moment, ants are very active, feeding on plum and cherry nectar. They can actually enter the flower where the nectar is hidden. Although ants are known to pollinate a few plants species, they are mostly 'nectar thieves'. The reason the ants do not usually pollinate flowers are twofold. First, they are so small in relation to the size of the flower that they do not seem to touch the anthers or stigmas when entering the flower, and pollen does not adhere well to the ants surface. Second, individual ants  do not travel between different flowers in a single bout of feeding, but just get enough to travel back to the nest from a single flower - notice the distended abdomen of the ants leaving the plum flower on the photo above. They seem to feed on nectar on any cup shaped flowers lacking specific mechanical obstructions to them entering the flower (such as labiatae, the pea family). In fact, aspects of flower shape might be adaptations by plants to exclude these generalistic nectar thieves.

 Black garden ants find Paeony buds secretions irresistible, and it is hard to spot a paeony bud without its handful of feeding ants.

 The ants are now also "milking" scale insects. They encourage the scale insects to excrete the honeydew by 'tickling' them with their antenna.

More information:

C.M. HERRERA, J. HERRERA and X. ESPADALER (1984) Nectar thievery by ants from Southern Spanish insect-pollinated flowers. Insectes Sociaux, 31: 142-154. Here.