Waterford Wildlife

Wednesday, 4th July 2012

More Cuckoos

Most people will be familiar with the peculiarities of the bird known here as the Cuckoo, an African migrant visitor during the summer months that uses the nests of other birds as a receptacle for its eggs, thus cuckolding the host bird into raising its young. Cuckoos occur not only among birds but also among insects; probably the best known ones are found in the nests of social insects. Among these are the pseudo-wasps and pseudo-bumblebees that are incapable of founding a nest of their own or bringing-up their own offspring. So, they colonise the nest of a related social insect species for this purpose. This occupation takes different forms in different species but the aim is the same – to ensure the feeding and upbringing of one insect's future generation at another's expense.

The cuckoo-wasp has no workers to feed the larvae and build a nest. However, the cuckoo-wasp still has to ensure the survival of her offspring. The female (or future queen) ensures her own future and that of her colony by finding a nest of the future host species. There have to be workers in it or at least their larvae or pupae about to hatch. The cuckoo-wasp needs these to rear its young. A scent or pheromone similar to those of the host wasps apparently enables her to enter their nest with impunity. This is the only explanation for the fact that the social wasps do not kill this intruder immediately as she attempts to enter. As soon as the cuckoo-wasp penetrates the nest, she usually kills the queen and settles in her place. From that moment the nest belongs to her. She then makes a start on her only task – egg laying. The workers that were already in the nest or are still hatching now serve the cuckoo-wasp. They begin to feed and look after its entire offspring as thoroughly as they would have done for members of their own species. Gradually the intruder's offspring become the majority in the colony and the original inhabitants die out. The Bumblebees also have their cuckoos – the very similar-looking cuckoo-bees. Cuckoo-bees also lack workers and they invade the nest of a related and similar bumblebee species to bring-up their larvae. Some species of cuckoo-bee appear to be more tolerant than others and allow the host bumblebee queen to live and in

others, the cuckoo-bee kills the host queen as with cuckoo-wasps. Even where both queens are living in the same nest and producing young, the real ruler is the cuckoo-bee queen while the original queen remains there more or less on sufferance with her eggs being eaten by the cuckoo-bee female.

Apart from these invasive cuckoos, colonies of social insects play host to and are inhabited by dozens of other insect species and hanger-ons'! Their relationships with their hosts are varied and sometimes very strange. The largest numbers of cohabitants and the greatest variety of species are found in ant colonies. These include species what provide sweet food for the ants (e.g. honeydew from aphids) but also intruders that prey on the young or ailing members of the host species. The experts divide these into three main groups; the symphiles – species encouraged by the hosts species such as aphids; synoeketes – that are tolerated by the hosts such as small woodlice (See picture) and syechthrans - species that prey and scavenge on the hosts such as small predatory and scavenging beetles. All of these and the above cuckoos are to be found throughout Waterford.