Urban Wildlife in Summer
12 June 2009British summers are notorious for their unreliability but, for all that, the days are long and the weather is often pleasantly warm and - once in a while, albeit very occasionally, almost hot. Humanity - across much of the world anyway - has made itself increasingly independent of climate and although we may choose to spend more time out of doors as the weather improves, in major respects our lives carry on the much same throughout the year. We may sleep a little less and be a little more active during daytime but the pattern of our existence does not change radically from one season to the next.
For much of the rest of the living world, however, life is pretty much determined by the number of hours of daylight and by the temperature. This is most obvious during the summer, when a vast number of creatures that we are scarcely even aware of for much of the year become active. Almost all of these are invertebrates, most of them members of the most numerous of all animal classes - the insects.
Most people, perhaps rather sadly, are only dimly aware of the incredible richness and variety of this awakening life and would be astounded to learn, for example, that even in the average urban garden, there are likely to be several thousand different species: a greater diversity, per square metre, than exists in any rain forest studied to date.
The vast majority of these creatures, of course, are very small. Most can be identified only by experts and very few have common names. This does not, however, make them any less significant. On the contrary, each of them has a vital role to play, whether they are helping with the process of plant decomposition, like many molluscs (slugs and snails), crustaceans such as woodlice, and some beetles; pollinating plants, like bees, wasps and flies; or belong to the huge group of hunters, whose activities keep the burgeoning numbers of plant feeders under control. Among these, the spiders and dragonflies are supreme, but other reasonably familiar carnivores include centipedes and millipedes, beetles such as ladybirds and some of the "true bugs" such as the water boatmen. But beyond these, there are tiny animals that most people may never even have heard of, even though they may be the most numerous of all in their back garden. These include other true bugs such as springtails - the most abundant of all insects anywhere in the world - barkflies and thrips.
Although such creatures as these live their lives in close proximity to us, we are pretty well oblivious of their existence. But before you empty the next lot of kitchen waste into your compost heap, take a closer look at what's going on inside it. Alternatively, sit by a pond for a few minutes or just spend some time in the sunshine at your local park or in your back garden, looking at the stream of flying visitors to the flowerbed. Whatever, if you take just a bit of time to examine the everyday things around us all you'll discover another world of ceaseless invertebrate activity and will almost certainly find insects and other creatures that you've never consciously noticed before. Some will be quite spectacular - like the hawthorn shieldbug or the green lacewing - and others comparatively dull, like the common froghopper, the nymphs of which form the frothy (and harmless) "cuckoo spit", found in spring and early summer on many garden plants. All have a part to play.
Among the insects that make their presence felt more obviously - and are therefore better known - are bees, wasps, butterflies and moths. The nests of social wasps are engineering marvels, but wondrous though they are, they are used for just one season - (what if the Belfast City Hall had been abandoned in 1906, the year it was built?!) - after which all the wasps in the colony die, with the exception of the queen who will found a new colony the following year. Nests can be several feet in diameter and can support up to 20,000 individuals. Wasps are active throughout the summer but don't really come to our attention until the end of the season, by which time they have left their nests and are in search of sugar, as a fuel to keep them going.
While the nest is in use, wasps are ruthless predators, using their fearsome stings to kill mosquitoes, aphids and even caterpillars - a good answer to give the next time you hear someone ask whether there is any point to wasps!
There are many species of wasp but most social wasps have bright warning colours - typically black and yellow - to deter possible predators. This protection is so effective that other creatures have evolved to mimic it, including the wasp beetle, which can often be found on umbelliferous plants (such as angelica or hogweed) in gardens.
Some hoverflies also resemble wasps and these are among many insects attracted to buddleja. Although this is not a native plant (it originates from China) and has a dubious reputation among the nature conservation community because of its invasiveness, its wildlife value cannot be disputed. It is well-known to act like a magnet to butterflies but many moths also find its heavy summer scent irresistible. Buddleja has become among the most familiar of all urban plants, seeding itself even in small crevices in walls and pavements. It is a mixed blessing but cannot be ignored.
At some point in mid-summer, most usually in late July, swarms of flying ants appear - in town and country alike. This is a once a year event and is linked to the mating of the small ant - Lasius niger. In some way which is not understood, both queens and male ants co-ordinate their emergence from nests across a wide area and take to the skies in millions. Many will fall prey to birds but the vast numbers involved ensure that enough will survive to mate and so perpetuate the species.
Many species of bird enjoy this bonanza including starlings, rooks and black-headed gulls but the main beneficiaries are probably the summer-visiting insect specialists like swallows, swifts and house martins. While swallows are not really associated with urban areas, both swifts and house martins have become more or less confined to areas of human settlement, although both species may still nest occasionally on maritime cliffs.
This brief explosion of vast numbers of ants into the air is paralleled in the plant kingdom as summer wanes by the production of millions of seeds. Summer and early autumn are rare periods of abundance in the natural world.